Academic burden and emotional problems among adolescents in China: a longitudinal mediation analysis

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The reasons underlying the educational impact are not well understood. This study aimed to explore loneliness, physical activity, and sleep as potential mediating pathways between academic burden and emotional problems in adolescents. Methods A longitudinal cohort study was conducted among middle and high school students in Taizhou City, Zhejiang Province, China with data collected at three time points (T1: April-May 2022, T2: September-October 2022, T3: February-May 2023). Depressive and anxiety symptoms were assessed using the Children’s Depression Inventory and the Generalized Anxiety Disorder-7, respectively. Structural equation modeling was employed to analyze the direct effect of academic burden (measured by study time and academic stress) on depressive and anxiety symptoms, and the indirect effects of academic burden via three mediators: loneliness, physical activity, and sleep. Results Using data from 2965 adolescents who completed all the three assessments, we found that higher academic stress at T1 was directly associated with more severe depressive symptoms at T3. Sleep (indirect effect 0.08, 95% CI 0.07 to 0.10), loneliness (0.07, 0.06 to 0.08) and physical activity (0.01, 0.002 to 0.01) mediated the association, accounting for 30.8%, 26.7% and 1.9% of the total effect of academic stress respectively. For anxiety symptoms, sleep (0.04, 0.03 to 0.05) and loneliness (0.03, 0.02 to 0.03) mediated the effect of academic stress with longitudinal mediation effect sizes of 34.4% and 20.8%, respectively. Study time was only associated with the outcomes indirectly via academic stress. Conclusions Our findings suggest that sleep, loneliness and physical activity could partly explain why adolescents with higher academic stress had more severe emotional problems, highlighting the importance of behavior and psychosocial differences driven by academic burden in explaining severity of mental health problems. The findings should raise awareness about the related risk factors of academic burden for adolescents, and strengthen calls for comprehensive strategies to improve adolescent mental health. Academic burden Adolescence Mental health Depression Anxiety Loneliness Physical activity Sleep Figures Figure 1 Introduction Globally, approximately one in seven adolescents aged 10–19 are affected by mental disorders, with depression and anxiety disorders collectively accounting for around 40% of cases [ 1 ]. In China, mental health issues among adolescents are widespread, with the prevalence of depressive and anxiety symptoms reported at 24.3% and 31.6% respectively [ 2 – 4 ]. These unresolved mental health challenges can significantly diminish the quality of life and persist into adulthood, exerting profound and lasting effects [ 5 ]. One influential model explaining deteriorating adolescent mental health is the "educational stressors hypothesis," which emphasizes the role of stress related to school and education in the increasing psychological distress among adolescents [ 6 ]. This hypothesis posits that the future social standing of adolescents is increasingly tied to their educational performance due to shifts toward knowledge economies and expanded higher education opportunities [ 6 , 7 ]. Consequently, various stressors related to schooling emerge, contributing to mental health adversities [ 7 – 9 ]. China's rapid socio-economic development over the past four decades, transitioning to knowledge economies, substantial educational expansion, and the booming off-campus tutoring industry have created a highly competitive educational environment. There are growing concerns about the impact of the heavy educational burden on mental health in Chinese adolescents. Studies have reported that the majority of students in China felt high or too much academic pressure, worried a lot about exams, found the volume of homework difficult to deal with, attended off-campus tutoring for two or more curriculum subjects per week, and were afraid of being punished by teachers and parents [ 10 , 11 ]. All these pressures were strongly related to depressive symptoms and anxiety symptoms [ 11 – 13 ]. The associations between academic burden and emotional problems have also been reported in other parts of Asia. For example, adolescents in Nepal facing academic stress are 2.4 times more likely to develop depression compared to their peers without such pressures [ 14 ]. A study in India found that academic stress had direct impact on changes in symptoms of generalized anxiety and panic among adolescents [ 15 ]. To understand why adolescents with higher academic burden experience more severe emotional problems, researchers need to examine possible mediating pathways through which academic pressure influences mental health. Three potential pathways are through loneliness, physical activity, and sleep. Students with greater perceived stress experience higher sense of loneliness [ 16 ]. A review about stress and perceived social isolation indicated that stress may play a co-causal or prodromic role in the development of loneliness [ 17 ]. As one of the strongest predictors of mental distress, loneliness often leads to more severe symptoms of depression and anxiety in adolescents [ 18 ].Another potential factor is the level of physical activity. The association between academic stress and physical exercise appears to be negative [ 19 ]. A systematic review based on 168 studies reported that psychological stress generally predicted less physical activity, especially in high-stress periods such as examination phases [ 20 ]. Less physical exercise may result in more severe depressive symptoms as exercise was found to effectively reduce depression scores but had no impact on anxiety scores in an overview of systematic reviews [ 21 ]. Sleep quality is also a potential factor influencing the association between academic stress and mental health. Sleep quality is influenced by multiple factors such as stress, and students under significant stress are more likely to suffer from sleep deprivation [ 22 ]. Prolonged insufficient or poor-quality sleep can worsen symptoms of depression and anxiety. For example, a meta-analytic evaluation of longitudinal studies revealed that non-depressed people with insomnia had a twofold risk of the onset of depression compared to people with no sleep difficulties [ 23 ]. Epidemiological studies reported that sleep disturbances, particularly insomnia, affected 50% of people with anxiety, and that insufficient sleep instigated or further exacerbated anxiety symptoms [ 24 ]. While research has made strides in understanding the associations between academic factors and adolescent mental health across various cultural and educational settings, their longitudinal impacts have not been thoroughly investigated. Many existing studies used cross-sectional design, and thus further longitudinal research is needed to elucidate the intricate associations. Furthermore, existing research often overlooks potential mediators that could play crucial roles in these associations. To improve mental well-being in youth, it is critical to investigate mechanisms by which academic factors drive adolescent mental health and identify potentially modifiable targets for intervention. The longitudinal cohort study among adolescents in Taizhou, China offered an opportunity to study the academic determinants of mental health problems and potential pathways in detail. Our study aimed to estimate the relative contribution of study time, academic stress, and three potential mediators – loneliness, physical activity, and sleep – on depressive and anxiety symptoms. We hypothesized that academic burden would drive depressive and anxiety symptoms in adolescents and that loneliness, physical activity and sleep would mediate the association between academic burden and youth mental health. Methods Study design and participants We conducted a longitudinal cohort study among secondary school students in Taizhou City, Zhejiang Province, China. Employing a multistage cluster sampling method, we selected five districts and counties, including one urban district (Jiaojiang), two county-level cities (Linhai and Yuhuan), and two counties (Tiantai and Sanmen). Within each district or county, three middle schools and three high schools were randomly selected. Two classes from each grade in each school were chosen to participate in the surveys. The study followed a longitudinal design with data collection occurring at three time points: April-May 2022 (T1), September-October 2022 (T2), and February-May 2023 (T3). We included students who were in the classes selected, capable of completing questionnaires, and willing to provide online informed consent. All of the participants were invited to complete online surveys via the Wenjuanxing platform ( https://www.wjx.cn ) which could automatically check before submission and avoid missing values. All participants gave informed consent at each wave. The research protocol received ethical approval from the Medical Ethics Committee of Taizhou Central Hospital (Affiliated Hospital of Taizhou University) (Approval No: 2022L-01-17). Measurements Academic burden relevant variables Academic stress was measured by the 16-item Educational Stress Scale for Adolescents (ESSA) [ 10 , 25 ]. The scale contains five domains, including pressure from study, workload, worry about grades, self-expectation, and despondency. Developed and validated in China, this scale serves as an appropriate instrument for quantitatively examining academic stress among Asian adolescents. Comprising 16 items, the scale adopts a 5-point Likert-type response format ranging from 1 = Strongly Agree to 5 = Strongly Disagree, with a total score range of 16–80. Higher scores indicate greater stress after reverse scoring. The scale demonstrated a Cronbach's α coefficient of 0.90 in our study. Study time was calculated as the total hours of the following activities per week, including time spent on homework assigned by school teachers, time spent on homework assigned by parents and off-campus tutors, and time spent on off-campus tutoring related to school subjects. Mental health outcomes Depressive symptoms during the last 2 weeks were measured by the 27-item Children’s Depression Inventory (CDI) [ 26 – 28 ]. The CDI is applicable to individuals aged 7 to 17 years old. The scale comprises 27 items and each item can be scored from 0 to 2. The total score ranges from 0 to 54, with higher scores indicating more severe depressive symptoms. The scale demonstrated a Cronbach's alpha coefficient of 0.90 in our study. Anxiety symptoms over the past two weeks were assessed by the Generalized Anxiety Disorder-7 (GAD-7) [ 29 ]. The GAD-7 is widely utilized for assessing anxiety symptoms. It consists of 7 items with a total score range of 0 to 21. Scoring involves assigning values of 0, 1, 2, and 3 to the response categories "not at all," "several days," "more than half the days," and "nearly every day," respectively. The scale exhibited a Cronbach's alpha coefficient of 0.93 Mediators Feelings of loneliness were assessed by the 3-Item UCLA Loneliness Scale (UCLA) [ 30 , 31 ]. The UCLA is a validated instrument to assess feelings of loneliness, including items of relational connectedness, social connectedness, and self-perceived isolation. The items were rated from 1 to 3 (1 = hardly ever, 2 = some of the time, 3 = often), and the total score ranged from 3 to 9, with higher scores indicative of heightened perceived loneliness. Physical activity (PA) was assessed by the frequency of physical exercise per week, and the index of the International Physical Activity Questionnaire - Short Form (IPAQ-SF) [ 32 – 34 ]. The former did not include exercise during physical education (PE) lessons, while the latter did. The IPAQ-SF provided the sum of days and minutes spent engaging in vigorous PA, moderate PA, and walking. The index for each PA modality using metabolic equivalent minutes per week (MET-minutes/week) was calculated as: MET-level × min of activity/day × days/week. The calculation was conducted thrice, yielding separate MET-minutes/week for each modality (walking = 3.3 METs, moderate PA = 4.0 METs, vigorous PA = 8.0 METs). The sum of these produced total MET-min/week for each student in the sample, with higher scores indicative of longer time and more intense exercise. Sleep was measured by the Pittsburgh Sleep Quality Index (PSQI) [ 35 , 36 ]. The PSQI comprises 19 items and can be divided into seven components, including duration of sleep, sleep disturbance, sleep latency, day dysfunction due to sleepiness, sleep efficiency, overall sleep quality, and use of sleep medication. Each component is scored on a scale of 0 to 3, with the cumulative score across components yielding the total PSQI score. Higher scores indicate poorer sleep quality. Covariates All covariates were based on data at T1. Sociodemographic characteristics included age (years at T1, continuous), gender (female, male), school (public school, non-public school), family economic status (high, middle, low), parents' marital status (married, others), parents' education (primary school or lower, middle school, high school, college or higher) and relationship with parents (good, normal or poor). The selection of covariates was based on past literature documenting their associations with adolescent educational burden, mental health problems and mediators. Statistical analysis For each participant, we included data on two academic burden exposures (study time and academic stress, measured at each participant’s first wave T1), three latent mediators (loneliness, physical activity and sleep, measured at each participant’s second wave T2), and two outcomes (depression and anxiety, measured at each participant’s final wave T3). We also included confounders related to the mediators and outcomes (Table 1 ). Table 1 Summary of variables Variables Details of variables Academic burden relevant variables (measured at T1) Study time The total hours of activities(time spent on homework assigned by school teachers, time spent on homework assigned by parents and off-campus tutors, and time spent on off-campus tutoring related to school subjects)per week. Academic stress Scores of ESSA, where higher scores indicate higher academic stress. Mediators (measured at T2) Loneliness Latent measure of loneliness using three items of UCLA (relational connectedness, social connectedness, and self-perceived isolation). Physical activity Latent measure of frequency of physical exercise per week (excluding exercise during PE lessons), and the index of IPAQ-SF (MET-minutes/week) (including exercise during PE lessons). Sleep Latent measure of sleep quality using seven components of PSQI (sleep duration, sleep disturbances, sleep latency, daytime dysfunction, sleep efficiency, sleep quality, and sleep medication). Mental health outcomes (measured at T3) Depressive symptoms Scores of CDI, where higher scores indicate more severe depressive symptoms. Anxiety symptoms Scores of GAD-7, where higher scores indicate more severe anxiety symptoms. Covariates Age, sex, type of school, family economic status, parents' marital status, parents’ education level, relationship with parents ESSA Educational Stress Scale for Adolescents ; UCLA UCLA Loneliness Scale ; IPAQ-SF International Physical Activity Questionnaire - Short Form ; MET-minutes/week metabolic equivalent minutes per week ; PSQI Pittsburgh Sleep Quality Index ; CDI Children’s Depression Inventory ; GAD-7 Generalized Anxiety Disorder-7 . We analyzed the distribution of all variables using mean, SD, frequency, and percentage. There were no missing data for the participants involved in the analyses as the Wenjuanxing platform automatically checked for missing values and reminded the participants before submission. In primary analyses, we modeled each of the mediators as continuous latent factors. Details of the factors used in the latent mediators, selected based on previous research[ 30 , 31 , 34 – 36 ], are provided in Table 1 . To understand the associations between variables before testing the full structural model, we analyzed paths between exposures, mediators, and outcomes in separate regression models, controlling for age, sex, type of school, parents' marital status, family economic status, parents’ education level, and relationship with parents. Statistical significance was set a priori at p < 0.05 with no adjustment for multiplicity. All hypothesized mediators were included in the final model simultaneously. Multiple mediation was used in the primary analysis due to its greater convenience, precision, and parsimony compared to multiple single mediation models, and it may also help reduce parameter bias caused by omitted variables [ 37 ]. Results are presented as standardized regression coefficients from the structural equation modeling (SEM). The coefficients were interpreted with regard to direction, magnitude, and statistical significance. The extent of mediation was described as the percentage of the total effect of an exposure mediated by a specific indirect effect. Based on previous research [ 38 – 40 ], the academic burden was treated sequentially, with study time preceding academic stress. We specified a correlational, rather than a directional, association between loneliness and physical activity, and between loneliness and sleep due to insufficient evidence regarding their directionality [ 41 , 42 ]. Physical activity was allowed to influence sleep [ 20 , 43 ]. The residual covariance between the two outcome variables is presented. Model fit was assessed using root mean square error of approximation (RMSEA), standardized root mean square residual (sRMR), comparative fit index (CFI), and Tucker-Lewis index (TLI). RMSEA and sRMR values of 0.06 or less indicated a good fit, although values up to 0.08 were considered acceptable[ 44 ]. For CFI and TLI, values greater than 0.95 reflected a good model fit. The structural equation modeling (SEM) was conducted using the lavaan package ver. 0.6–16 in R version 4.3.1. In sensitivity analyses, we separately conducted three mediation models with the dimensions or items of each latent mediator added in a single structural equation model. For example, for the mediating role of loneliness, the three loneliness items were tested as mediators in one model. The models were similar to those in the primary analyses except for the mediating variables to evaluate how individual factors of each mediator affected results. Results A total of 2965 participants took part in all the three assessments from T1 to T3, who were included in the current analysis. Figure S1 shows the flow of participants through each wave of the study. Table 2 presents the characteristics of participants in the final sample. The mean age of respondents was 15.2 years (SD 1.7), with 1423 (48.0%) being female at baseline (T1). Most of the participants were in public school (68.9%) and had middle or high family economic status (94.8%). Table 2 Characteristics of participants in the analysis sample Variables Overall (n = 2,965) Variables Overall (n = 2,965) T1 Relationship with father Age, years 15.2 (1.7) Good 2,292(77.3%) Sex Normal/poor 673(22.7%) Female 1,423(48.0%) Study time per week (homework and off-campus tutoring), hours 30.8 (17.9) Male 1,542(52.0%) Academic stress 52.6 (11.2) School T2 Public school 2,044(68.9%) Loneliness Non-public school 921(31.1%) Relational connectedness 1.5 (0.6) Parents' marital status Social connectedness 1.5 (0.6) Married 2,678 (90.3%) Self-perceived isolation 1.5 (0.6) Others 287 (9.7%) Physical activity 2.0(2.0) Family economic status Frequency of physical activity per week (excluding physical education classes) 2.0(2.0) High 422(19.3%) Middle 1,654(75.5%) Low 114 (5.2%) Weekly physical activity, MET-minutes/week 1,174.2(1,869.0) Father’s education Primary school or lower 357(12.0%) Sleep Middle school 1,181(39.8%) Sleep duration 0.5 (0.7) High school 843(28.4%) Sleep disturbances 0.7 (0.6) College or higher 584(19.7%) Sleep latency 0.9 (0.9) Mother’s education Daytime dysfunction 1.0 (1.0) Primary school or lower 467(15.8%) Sleep efficiency 0.3 (0.8) Middle school 1,137(38.3%) Sleep quality 0.8 (0.8) High school 789(26.6%) Sleep medication 0.1 (0.4) College or higher 572(19.3%) T3 Relationship with mother Depressive symptoms 11.1 (8.2) Good 2,518(84.9%) Anxiety symptoms 4.8 (4.3) Normal/poor 447(15.1%) Data are mean (SD) or n (%) unless otherwise indicated. MET-minutes/week stands for metabolic equivalent minutes per week. Using maximum likelihood estimation with 5000 bootstrapped iterations, the final full structural model exhibited good model fit (RMSEA 0.048, 95% CI 0.046–0.050, sRMR 0.035, CFI 0.986, TLI 0.979). In the preliminary analysis (Table 3 ) and the final model (Fig. 1 ; Table 4 ), more academic stress was directly associated with higher levels of perceived loneliness, less physical activity, worse sleep, and more severe depressive and anxiety symptoms. In the final model, pathways from academic stress to loneliness and subsequently to depressive symptoms (indirect effect 0.07, 95% CI 0.06 to 0.08, effect size 26.7%) and anxiety symptoms (indirect effect 0.03, 95% CI 0.02 to 0.03, effect size 20.8%) were observed. Moreover, physical activity mediated the effect of academic stress on depressive symptoms (indirect effect 0.01, 95% CI 0.002 to 0.01), accounting for 1.9% of the total effect of academic stress on depressive symptoms. However, physical activity did not significantly mediate the association between academic stress and anxiety symptoms. The hypothesized mediation pathways, proceeding from academic stress to sleep and ultimately to depressive symptoms (indirect effect 0.08, 95% CI 0.07 to 0.10) and anxiety symptoms (indirect effect 0.04, 95% CI 0.03 to 0.05), were empirically substantiated, with longitudinal mediation effect sizes of 30.8% and 34.4%, respectively. Table 3 Associations between exposures, mediators and outcomes Associations Effect study time > loneliness 0.00 (-0.00, 0.00) academic stress > loneliness 0.03 (0.03, 0.03) * study time > physical activity 0.00 (-0.00, 0.00) academic stress > physical activity -0.01 (-0.02, -0.01) * study time > sleep 0.00 (-0.00, 0.00) academic stress > sleep 0.04 (0.03, 0.04) * study time > depressive symptoms 0.02 (0.003, 0.03) * academic stress > depressive symptoms 0.27 (0.24, 0.29) * loneliness > depressive symptoms 4.42 (4.15, 4.69) * physical activity > depressive symptoms -0.25 (-2.48, 1.99) sleep > depressive symptoms 4.44 (4.16, 4.72) * study time > anxiety symptoms 0.00 (-0.01, 0.01) academic stress > anxiety symptoms 0.13 (0.11, 0.14) * loneliness > anxiety symptoms 1.82 (1.67, 1.97) * physical activity > anxiety symptoms -0.10 (-0.99, 0.80) sleep > anxiety symptoms 2.03 (1.88, 2.19) * > indicates the direction of the regression path, i.e. study time predicts loneliness. * p value < 0.05. Table 4 Standardized regression coefficients for the direct and indirect effects for the final full structural model Academic stress Loneliness Physical activity Sleep Depressive symptoms Anxiety symptoms Mediators Loneliness (direct effect) - - - - 2.49 (2.17 to 2.79) * 0.90 (0.71 to 1.09) * Physical activity (direct effect) - - - -0.12 (-0.17 to -0.06) * -0.45 (-0.74 to -0.17) * 0.02 (-0.14 to 0.18) Indirect effect via sleep - - - - -0.26 (-0.38 to -0.14) * -0.13 (-0.20 to -0.07) * Sleep (direct effect) - - - - 2.23 (1.91 to 2.55) * 1.16 (0.94 to 1.37) * Academic stress Direct effect - 0.03 (0.03 to 0.03) * -0.01 (-0.02 to -0.01) * 0.04 (0.03 to 0.04) * 0.11 (0.08 to 0.13) * 0.06 (0.04 to 0.07) * Total indirect effects - - - - 0.16 (0.14 to 0.18) * 0.07 (0.06 to 0.08) * Via loneliness - - - - 0.07 (0.06 to 0.08) * 0.03 (0.02 to 0.03) * Via physical activity - - - 0.001 (0.001 to 0.002) * 0.01 (0.002 to 0.01) * 0.00 (-0.00 to 0.00) Via sleep - - - - 0.08 (0.07 to 0.10) * 0.04 (0.03 to 0.05) * Via physical activity, and sleep - - - - 0.003 (0.001 to 0.01) * 0.001 (0.001 to 0.002) * Total effect - - - - 0.27 (0.24 to 0.29) * 0.13 (0.11 to 0.14) * Study time Direct effect 0.11 (0.08 to 0.13) * 0.00 (-0.00 to 0.00) 0.00 (-0.00 to 0.00) 0.00 (-0.00 to 0.00) 0.01 (-0.00 to 0.03) -0.00 (-0.01 to 0.01) Total indirect effects - - - - 0.00 (-0.01 to 0.01) 0.00 (-0.01 to 0.01) Via loneliness - - - - 0.00 (-0.00 to 0.01) 0.00 (-0.00 to 0.00) Via physical activity - - - 0.00 (0.00 to 0.00) 0.00 (-0.00 to 0.00) 0.00 (-0.00 to 0.00) Via sleep - - - - 0.00 (-0.01 to 0.01) 0.00 (-0.00 to 0.00) Via physical activity, and sleep - - - - 0.00 (-0.00 to 0.00) 0.00 (-0.00 to 0.00) Via academic stress - 0.003 (0.002 to 0.004) * -0.001 (-0.002 to -0.001) * 0.004 (0.003 to 0.01) * 0.01 (0.01 to 0.02) * 0.01 (0.004 to 0.01) * Total effect - - - - 0.02 (0.001 to 0.03) * -0.00 (-0.01 to 0.01) Covariances Loneliness - - -0.12 (-0.17 to -0.07) * 0.44 (0.39 to 0.48) * - - Depressive symptom - - - - - 10.56 (9.33 to 11.72) * * p value < 0.05. In the preliminary analysis (Table 3 ), longer study time was directly associated with more severe depressive symptoms, whereas in the final model, the results showed no significant direct effect of study time on any outcomes or mediators (Fig. 1 ; Table 4 ). However, longer study time had a positive effect on academic stress (β = 0.11, 95% CI 0.08 to 0.13) and indirect effects via academic stress on loneliness, physical activity, sleep, depressive symptoms, and anxiety symptoms. Greater loneliness was associated with more severe depressive symptoms (β = 2.49, 95% CI 2.17 to 2.79) and anxiety symptoms (β = 0.90, 95% CI 0.71 to 1.09) (Fig. 1 ; Table 4 ). Loneliness was correlated with physical activity (β=-0.12, 95% CI -0.17 to -0.07) and sleep (β = 0.44, 95% CI 0.39 to 0.48) in the final model. Physical activity had direct effect on depressive symptoms (β=-0.45, 95% CI -0.74 to -0.17) but not anxiety symptoms. More physical activity was associated with better sleep (β=-0.12, 95% CI -0.17 to -0.06). Sleep had direct effects on depressive symptoms (β = 2.23, 95% CI 1.91 to 2.55) and anxiety symptoms (β = 1.16, 95% CI 0.94 to 1.37). In our sensitivity analyses, the results from the single mediator models were largely consistent with the final model estimates (Table S1 ). All the three items of loneliness measure (relational connectedness, social connectedness, and self-perceived isolation) mediated the effects of academic stress on depressive and anxiety symptoms (Figure S2). Frequency of physical exercise excluding PE lessons mediated the impact of academic stress on depressive and anxiety symptoms, but weekly physical activity level including PE lessons (IPAQ-SF) did not (Figure S3). Academic stress had indirect effects via sleep duration, sleep disturbances, sleep latency, daytime dysfunction, and sleep quality on depressive symptoms, while via sleep duration, sleep disturbances, sleep latency, and daytime dysfunction on anxiety symptoms (Figure S4). The effect sizes for the pathways through daytime dysfunction and sleep disturbances were larger than the other dimensions of sleep (Table S1 ). The association between study time and depressive symptoms was not mediated by loneliness, physical activity and sleep. Discussion Our study conducted a comprehensive investigation into the longitudinal association between academic burden and symptoms of depression and anxiety and potential mediating pathways among middle and high school students in Taizhou, China. The results of this study indicated that higher academic stress was associated with more severe depressive and anxiety symptoms. Sleep, loneliness and physical activity mediated the association between academic stress and depressive symptoms, accounting for 30.8%, 26.7% and 1.9% of the total effect of academic stress respectively. Sleep and loneliness also mediated the association between academic stress and anxiety symptoms, with longitudinal mediation effect sizes of 34.4% and 20.8%, respectively. Study time was only associated with the outcomes indirectly via academic stress, reflecting that educational stress is likely to be more relevant to emotional problems than actual study time. In both preliminary analysis and structural model, we observed the mediating role of sleep in the associations between academic stress and symptoms of depression and anxiety, underscoring the importance of adequate and high-quality sleep for psychological well-being. Multiple factors contribute to the results. On the one hand, academic stress may influence sleep quality from biological aspects. Research by Adam et al. suggested that academic stress can disrupt an individual's biological clock, consequently affecting sleep quality[ 45 ]. According to psychobiological models, academic stress, often marked by worry and rumination, may be related to mental hyperarousal which is a key factor for insomnia[ 46 ]. On the other hand, the impact of sleep on symptoms of depression and anxiety aligns with findings from existing literature. A meta-analytic evaluation of longitudinal studies found that non-depressed individuals with insomnia had a twofold risk of developing depression compared to those with no sleep difficulties[ 47 ]. Similarly, insomnia was found to be a major predictor for the onset of anxiety in a meta-analysis[ 48 ]. Although psychophysiological mechanisams for the associations are still not clear, researchers suggested that the impairment of sleep-wake regulating neural circuitries may result in changes in emotional reactivity[ 49 ]. Moreover, in our sensitivity analyses, several domains of sleep, particularly in the realms of daytime dysfunction and sleep disturbances, were significant mediators of the associations between academic stress and emotional problems. They may be red flags to target for preventing depression and anxiety among adolescents in future studies. Loneliness mediated the association between academic stress and symptoms of depression and anxiety, accounting for over 20% of the total effect of academic stress. This suggests that people with higher academic stress had more severe emotional problems in part because they had greater loneliness. Several factors may contribute to the observed associations. Academic stress, such as worrying a lot about exams, future education and employment, and being punished by teachers and parents, is inherent aspects of the educational environment in China [ 10 ]. Educational expectations are one of the main sources of stress in adolescents, and those with poor academic performance are more likely to have weak social connectedness and feel lonely [ 50 ]. Students experiencing high levels of academic stress may withdraw from social interactions or perceive a lack of support from peers and teachers, contributing to increased feelings of loneliness 3 . Additionally, previous studies indicate a close association between feelings of loneliness and symptoms of depression and anxiety. Individuals experiencing loneliness are more prone to exhibit symptoms of depression such as low mood, loss of interest, and self-deprecation [ 51 , 52 ]. Loneliness is also closely associated with symptoms of anxiety, including worries about the future, social anxiety, and doubts about one's own abilities [ 53 , 54 ]. Our study extends beyond previous research and found that students who perceived deficits in social connections or experienced feelings of isolation were more vulnerable to the negative effects of academic stress on mental health. The results are consistent with a study in healthcare students and early-career professionals which reported that loneliness mediated the adverse impact of psychological stress on depressive and anxiety symptomatology during COVID-19 [ 55 ]. Noteworthy, the mediating role of physical activity in the association between academic stress and mental health outcomes is complex. We found a significant association between reduced physical activity and more severe depressive symptoms but not with anxiety symptoms. Consistent with previous studies, the risk of depression may be reduced by physical activity [ 56 , 57 ]. A meta-analysis found that if the current physical activity recommendations had been achieved by less active individuals, 11.5% of depression cases could have been prevented [ 56 ]. Increased physical activity may alleviate depressive symptoms through the release of neurotransmitters such as dopamine and endorphins [ 58 ]. However, there is a lack of significant association between physical activity and anxiety symptoms in our study. The result is consistent with a review which reported that vigorous exercise led to diminished depressive symptoms with no impact on anxiety among adolescents when compared to no intervention [ 21 ]. Although physical activity mediated the association between academic stress and depressive symptoms, the effect size for the pathway was smaller than those for the other two mediators, indicating that sleep and loneliness may play a more important role in the relationship. In further analysis, we found that frequency of physical exercise per week not including PE lessons mediated the association between academic stress and depressive and anxiety symptoms. However, academic stress did not significantly affect the outcomes via total MET-min per week which included exercise during PE lessons. Academic stress might reduce leisure physical activity but had less impact on the total intensity of exercise since PE lesson is a compulsory subject in school. Additionally, despite the potential benefits of physical activity, students may experience less pleasure through doing exercise when it becomes a task and relates to their scores at school [ 59 ]. In a systematic review, leasure-time physical activity was found to be the most effective domain for improving mental health, while occupational or domestic physical activity was related to worse mental health outcomes [ 60 ]. We observed that study time did not have a significant direct impact on the mediators or outcomes, but it exerted an influence through academic stress. Students who spend longer hours studying often experience higher academic stress. The study time we measured contained time spent on homework assigned by school teachers, parents and off-campus tutors, and time spent on off-campus tutoring related to school subjects. When the information and tasks placed on working memory exceed its capacity, cognitive overload can occur, which often triggers the stress response [ 61 ]. Multiple tasks at the same time can generate a feeling of lack of time to finish homework or to have a good performance. In addition, the additional learning tasks assigned by parents and off-campus tutors reduce the time available for relaxation and social activities, and may impair a sense of choice in adolescents with respect to their behavior, which in turn increase academic stress. Study time had a weaker effect on the outcomes, reflecting that academic stress may be better than study time for differentiating between adolescents with different levels of academic burden and may be a stronger predictor of mental health problems than measures of objective workload. Strengths of this study are three waves of longitudinal data, test of multiple competing hypotheses, and use of validated scales. While there is consistent evidence that adolescents with greater academic burden are more likely to experience emotional problems [ 7 , 9 , 12 , 62 ], a notable gap exists in empirically investigating factors mediating the associations. Importantly, our evaluation of potential mediators sheds light on the role of sleep, loneliness and physical activity in driving the associations. This research fills the gap in the literature and provides information for the development of targeted interventions aimed at mitigating the adverse effects of academic burden on mental health of adolescents. In spite of these advantages, we should acknowledge several limitations. Firstly, our research was conducted in the specific cultural and educational settings, which may not fully represent the experiences of adolescents in other regions or cultural environment. Secondly, although validated measures were used to evaluate academic stress, meditators and mental health outcomes, potential response bias and self-report bias might still exist. Thirdly, the pandemic might have some impact on the results. However, our study was conducted during a relatively stable period of the pandemic and schools in Taizhou were reopened before the start of the survey at T1, and thus we did not suppose the effect to be profound. Finally, while factors including loneliness, physical activity, and sleep quality have been identified as mediators influencing the association between academic stress and emotional disturbances, the relationships between study time and mental health problems remain incompletely understood. Further research designed to measure other potentially modifiable factors on the pathway from actual study burden to emotional and behavioral problems should be investigated. Our study have practical implications for guiding educational policies, intervention development and school management practices for adolescents, especially those in a highly competitive educational environment. Given the association between academic stress and depressive and anxiety symptoms, schools should strengthen psychological health education and provide psychological support services to help students effectively manage stress and promote mental well-being. Our findings also underscore the responsibility of educational policymakers to carry out reforms to reduce students' academic pressure. This may include reassessing curriculum loads and devising more flexible learning schedules to ensure that students' academic burden is not excessively heavy. More educational burden reduction programs should be designed and implemented, such as the Double Reduction campaign in China aiming at reducing heavy workloads and excessive off-campus tutoring for students [ 63 ]. Moreover, our study found key mediators which could be important targets for intervention, including sleep, loneliness and physical activity. Parents and school administrators should strengthen collaboration and offer guidance on sleep management to ensure that students obtain sufficient and high-quality sleep and reduce daytime dysfunction. More social support and opportunities for social activities should also be provided to enhance social connectedness and reduce loneliness. Apart from exercise during PE lessons, parents and teachers can encourage students to engage in leisure-time exercise by themselves as it is the domain of physical activity most associated with mental health [ 60 ]. By recognizing and addressing the impact of academic burden on mental health, policymakers, educators and parents can work together to create a suitable educational environment which lays foundation for adolescents’ long-term success and happiness. Conclusions In summary, this study found that poorer sleep, higher loneliness and less physical activity experienced by adolescents with greater academic burden gave rise to emotional problems. Our results contribute to a deeper understanding of the complex pathways linking academic burden and mental health outcomes among adolescents. The findings underscore the importance of addressing academic burden and provide valuable insights for the development of comprehensive interventions to protect students' mental well-being. Apart from direct strategies to reduce study time and alleviate academic stress, effective interventions to deal with mediating factors, such as ensuring high-quality sleep, mitigating loneliness and stimulating voluntary physical activities in leisure time, are also beneficial to adolescent mental health. Abbreviations SEM Structural equation modeling RMSEA Root mean square error of approximation sRMR Standardized root mean square residual CFI Comparative fit index TLI Tucker-Lewis index ESSA Educational Stress Scale for Adolescents UCLA UCLA Loneliness Scale IPAQ-SF International Physical Activity Questionnaire - Short Form MET-minutes/week Metabolic equivalent minutes per week PSQI Pittsburgh Sleep Quality Index CDI Children’s Depression Inventory GAD-7 Generalized Anxiety Disorder-7 Declarations Ethics approval and consent to participate The study was approved by the Ethics Committee of Taizhou Central Hospital (2022L-01-17), and all methods were carried out in accordance with relevant guidelines and regulations. All participants and parents or legal guardians of the children participating in our study provided informed consent prior to study participation. Informed consent procedures were used to collect all study data. Consent for publication All authors approved the final manuscript for publication. Availability of data and materials The data that support the findings of this study are available from the corresponding author upon reasonable request. Competing interests The authors declare that they have no competing interests. Funding JW was sponsored by the China Medical Board (grant number #22-472) and the National Natural Science Foundation of China (grant number 72104053). CF was sponsored by the General Project of Shanghai Municipal Health Commission (grant number 202240115). HL and XC were sponsored by the Special Support Program for High Level Talents in Taizhou (grant number TZ2022-2). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Authors' contributions JW, XC, and CF designed the study and formulated the outline and structure of the article. JW, ZW, and YY conducted data collection and analysis, as well as drafted the manuscript. TW, HL and WZ interpreted the results and critically reviewed the manuscript. XC and CF reviewed the manuscript. All authors align with the the final manuscript. Acknowledgements We express our heartful gratitude to the study participants for their invaluable contributions. We also sincerely appreciate the dedication and hard work of the Taizhou City Center for Disease Prevention and Control (CDC) and the local CDCs. References Adolescent mental health statistics. In: UNICEF DATA. https://data.unicef.org/topic/child-health/mental-health/. Accessed 6 Dec 2023 Wang C, Zhang P, Zhang N. Adolescent mental health in China requires more attention. The Lancet Public health 5:e637–e637 ADOLESCENT MENTAL HEALTH | UNICEF China. https://www.unicef.cn/en/reports/adolescent-mental-health. Accessed 18 Nov 2023 Wang M, Mou X, Li T, Zhang Y, Xie Y, Tao S, Wan Y, Tao F, Wu X. 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J Fam Psychol 21:4–19 Riemann D, Nissen C, Palagini L, Otte A, Perlis ML, Spiegelhalder K. The neurobiology, investigation, and treatment of chronic insomnia. Lancet Neurol 14:547–558 Baglioni C, Battagliese G, Feige B, Spiegelhalder K, Nissen C, Voderholzer U, Lombardo C, Riemann D. Insomnia as a predictor of depression: a meta-analytic evaluation of longitudinal epidemiological studies. J Affect Disord 135:10–19 Hertenstein E, Feige B, Gmeiner T, et al. Insomnia as a predictor of mental disorders: A systematic review and meta-analysis. Sleep Med Rev 43:96–105 Riemann D, Spiegelhalder K, Feige B, Voderholzer U, Berger M, Perlis M, Nissen C. The hyperarousal model of insomnia: a review of the concept and its evidence. Sleep Med Rev 14:19–31 Lan Z, Liu H, Huang X, Wang Q, Deng F, Li J. The Impact of Academic Pressure and Peer Support on Adolescents’ Loneliness: A Polynomial Regression and Response Surface Analysis. Psychol Res Behav Manag 16:4617–4627 Heinrich LM, Gullone E. The clinical significance of loneliness: a literature review. Clin Psychol Rev 26:695–718 Cacioppo JT, Hawkley LC. Perceived social isolation and cognition. Trends Cogn Sci 13:447–454 Hawkley LC, Cacioppo JT. Loneliness matters: a theoretical and empirical review of consequences and mechanisms. Ann Behav Med 40:218–227 Matthews T, Danese A, Wertz J, Odgers CL, Ambler A, Moffitt TE, Arseneault L. Social isolation, loneliness and depression in young adulthood: a behavioural genetic analysis. Soc Psychiatry Psychiatr Epidemiol 51:339–348 Bonilla-Sierra P, Manrique-G A, Hidalgo-Andrade P, Ruisoto P. Psychological Inflexibility and Loneliness Mediate the Impact of Stress on Anxiety and Depression Symptoms in Healthcare Students and Early-Career Professionals During COVID-19. Front Psychol 12:729171 Pearce M, Garcia L, Abbas A, et al. Association Between Physical Activity and Risk of Depression: A Systematic Review and Meta-analysis. JAMA Psychiatry 79:550–559 Heissel A, Heinen D, Brokmeier LL, et al. Exercise as medicine for depressive symptoms? A systematic review and meta-analysis with meta-regression. Br J Sports Med 57:1049–1057 Penedo FJ, Dahn JR. Exercise and well-being: a review of mental and physical health benefits associated with physical activity. Curr Opin Psychiatry 18:189–193 Richards J, Jiang X, Kelly P, Chau J, Bauman A, Ding D. Don’t worry, be happy: cross-sectional associations between physical activity and happiness in 15 European countries. BMC Public Health 15:53 Teno SC, Silva MN, Júdice PB. Physical activity and sedentary behaviour-specific domains and their associations with mental health in adults: a systematic review. Advances in Mental Health 0:1–28 Bodys-Cupak I, Grochowska A, Zalewska-Puchaa J, Majda A. Stress and coping strategies of medical students during their first clinical practice – a pilot study. Medical Studies 35:294–303 Xu J, Wang H, Liu S, Hale ME, Weng X, Ahemaitijiang N, Hu Y, Suveg C, Han ZR. Relations among family, peer, and academic stress and adjustment in Chinese adolescents: A daily diary analysis. Developmental psychology 59:1346–1358 The General Office of the CPC Central Committee and the General Office of the State Council. The opinions on easing the burden of excessive homework and off-campus tutoring for students undergoing compulsory education. Beijing: Ministry of Education of the People's Republic of China.http://www.moe.gov.cn/jyb_xxgk/moe_1777/moe_1778/202107/t20210724_546576.html. Accessed 10 May 2024 (in Chinese) Additional Declarations No competing interests reported. Supplementary Files Additionalfile1.docx Additional file 1: Figure S1. Flow chart showing sample size included in the study. Table S1. Effect size and standardized regression coefficients for the indirect effects for academic stress and study time on depressive symptoms and anxiety symptoms via measurement factors of the latent variables (loneliness, physical activity, and sleep). Figure S2. Standardized coefficients for the direct effects for model 1 (loneliness mediators). Figure S3.Standardized coefficients for the direct effects for model 2 (physical activity mediators). Figure S4. Standardized coefficients for the direct effects for the model 3 (sleep mediators) Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Note: Single-headed arrows indicate regression paths, double-headed arrows indicate covariances, ovals represent latent variables, and rectangles represent measured variables. Coefficients are shown for statistically significant paths, whereas paths with dashed lines were not significant.\u003c/p\u003e","description":"","filename":"OnlineFigure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4435974/v1/0350fe8a3647698055918630.png"},{"id":57729837,"identity":"f5099655-bc1a-4888-9a35-596dea2a6b64","added_by":"auto","created_at":"2024-06-04 21:56:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1239537,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4435974/v1/10dbcf8f-c354-4a1c-800b-3936cf0306fc.pdf"},{"id":57727793,"identity":"06b5ece1-2e86-4751-b6c9-43b2360dfcff","added_by":"auto","created_at":"2024-06-04 21:40:02","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":4073625,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdditional file 1: Figure S1. \u003c/strong\u003eFlow chart showing sample size included in the study.\u003cstrong\u003e Table S1. \u003c/strong\u003eEffect size and standardized regression coefficients for the indirect effects for academic stress and study time on depressive symptoms and anxiety symptoms via measurement factors of the latent variables (loneliness, physical activity, and sleep). \u003cstrong\u003eFigure S2.\u003c/strong\u003e Standardized coefficients for the direct effects for model 1 (loneliness mediators).\u003cstrong\u003e Figure S3.\u003c/strong\u003eStandardized coefficients for the direct effects for model 2 (physical activity mediators).\u003cstrong\u003e Figure S4.\u003c/strong\u003e Standardized coefficients for the direct effects for the model 3 (sleep mediators)\u003c/p\u003e","description":"","filename":"Additionalfile1.docx","url":"https://assets-eu.researchsquare.com/files/rs-4435974/v1/5daa8d8443a7ab28f0303859.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Academic burden and emotional problems among adolescents in China: a longitudinal mediation analysis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGlobally, approximately one in seven adolescents aged 10\u0026ndash;19 are affected by mental disorders, with depression and anxiety disorders collectively accounting for around 40% of cases [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In China, mental health issues among adolescents are widespread, with the prevalence of depressive and anxiety symptoms reported at 24.3% and 31.6% respectively [\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. These unresolved mental health challenges can significantly diminish the quality of life and persist into adulthood, exerting profound and lasting effects [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOne influential model explaining deteriorating adolescent mental health is the \"educational stressors hypothesis,\" which emphasizes the role of stress related to school and education in the increasing psychological distress among adolescents [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. This hypothesis posits that the future social standing of adolescents is increasingly tied to their educational performance due to shifts toward knowledge economies and expanded higher education opportunities [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Consequently, various stressors related to schooling emerge, contributing to mental health adversities [\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. China's rapid socio-economic development over the past four decades, transitioning to knowledge economies, substantial educational expansion, and the booming off-campus tutoring industry have created a highly competitive educational environment. There are growing concerns about the impact of the heavy educational burden on mental health in Chinese adolescents. Studies have reported that the majority of students in China felt high or too much academic pressure, worried a lot about exams, found the volume of homework difficult to deal with, attended off-campus tutoring for two or more curriculum subjects per week, and were afraid of being punished by teachers and parents [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. All these pressures were strongly related to depressive symptoms and anxiety symptoms [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The associations between academic burden and emotional problems have also been reported in other parts of Asia. For example, adolescents in Nepal facing academic stress are 2.4 times more likely to develop depression compared to their peers without such pressures [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. A study in India found that academic stress had direct impact on changes in symptoms of generalized anxiety and panic among adolescents [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo understand why adolescents with higher academic burden experience more severe emotional problems, researchers need to examine possible mediating pathways through which academic pressure influences mental health. Three potential pathways are through loneliness, physical activity, and sleep. Students with greater perceived stress experience higher sense of loneliness [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. A review about stress and perceived social isolation indicated that stress may play a co-causal or prodromic role in the development of loneliness [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. As one of the strongest predictors of mental distress, loneliness often leads to more severe symptoms of depression and anxiety in adolescents [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].Another potential factor is the level of physical activity. The association between academic stress and physical exercise appears to be negative [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. A systematic review based on 168 studies reported that psychological stress generally predicted less physical activity, especially in high-stress periods such as examination phases [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Less physical exercise may result in more severe depressive symptoms as exercise was found to effectively reduce depression scores but had no impact on anxiety scores in an overview of systematic reviews [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Sleep quality is also a potential factor influencing the association between academic stress and mental health. Sleep quality is influenced by multiple factors such as stress, and students under significant stress are more likely to suffer from sleep deprivation [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Prolonged insufficient or poor-quality sleep can worsen symptoms of depression and anxiety. For example, a meta-analytic evaluation of longitudinal studies revealed that non-depressed people with insomnia had a twofold risk of the onset of depression compared to people with no sleep difficulties [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Epidemiological studies reported that sleep disturbances, particularly insomnia, affected 50% of people with anxiety, and that insufficient sleep instigated or further exacerbated anxiety symptoms [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhile research has made strides in understanding the associations between academic factors and adolescent mental health across various cultural and educational settings, their longitudinal impacts have not been thoroughly investigated. Many existing studies used cross-sectional design, and thus further longitudinal research is needed to elucidate the intricate associations. Furthermore, existing research often overlooks potential mediators that could play crucial roles in these associations. To improve mental well-being in youth, it is critical to investigate mechanisms by which academic factors drive adolescent mental health and identify potentially modifiable targets for intervention. The longitudinal cohort study among adolescents in Taizhou, China offered an opportunity to study the academic determinants of mental health problems and potential pathways in detail. Our study aimed to estimate the relative contribution of study time, academic stress, and three potential mediators \u0026ndash; loneliness, physical activity, and sleep \u0026ndash; on depressive and anxiety symptoms. We hypothesized that academic burden would drive depressive and anxiety symptoms in adolescents and that loneliness, physical activity and sleep would mediate the association between academic burden and youth mental health.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design and participants\u003c/h2\u003e \u003cp\u003eWe conducted a longitudinal cohort study among secondary school students in Taizhou City, Zhejiang Province, China. Employing a multistage cluster sampling method, we selected five districts and counties, including one urban district (Jiaojiang), two county-level cities (Linhai and Yuhuan), and two counties (Tiantai and Sanmen). Within each district or county, three middle schools and three high schools were randomly selected. Two classes from each grade in each school were chosen to participate in the surveys. The study followed a longitudinal design with data collection occurring at three time points: April-May 2022 (T1), September-October 2022 (T2), and February-May 2023 (T3). We included students who were in the classes selected, capable of completing questionnaires, and willing to provide online informed consent. All of the participants were invited to complete online surveys via the Wenjuanxing platform (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.wjx.cn\u003c/span\u003e\u003cspan address=\"https://www.wjx.cn\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e) which could automatically check before submission and avoid missing values. All participants gave informed consent at each wave. The research protocol received ethical approval from the Medical Ethics Committee of Taizhou Central Hospital (Affiliated Hospital of Taizhou University) (Approval No: 2022L-01-17).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eMeasurements\u003c/h2\u003e \u003cp\u003e \u003cb\u003eAcademic burden relevant variables\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAcademic stress was measured by the 16-item Educational Stress Scale for Adolescents (ESSA) [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The scale contains five domains, including pressure from study, workload, worry about grades, self-expectation, and despondency. Developed and validated in China, this scale serves as an appropriate instrument for quantitatively examining academic stress among Asian adolescents. Comprising 16 items, the scale adopts a 5-point Likert-type response format ranging from 1\u0026thinsp;=\u0026thinsp;Strongly Agree to 5\u0026thinsp;=\u0026thinsp;Strongly Disagree, with a total score range of 16\u0026ndash;80. Higher scores indicate greater stress after reverse scoring. The scale demonstrated a Cronbach's α coefficient of 0.90 in our study.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eStudy time was calculated as the total hours of the following activities per week, including time spent on homework assigned by school teachers, time spent on homework assigned by parents and off-campus tutors, and time spent on off-campus tutoring related to school subjects.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eMental health outcomes\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eDepressive symptoms during the last 2 weeks were measured by the 27-item Children\u0026rsquo;s Depression Inventory (CDI) [\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The CDI is applicable to individuals aged 7 to 17 years old. The scale comprises 27 items and each item can be scored from 0 to 2. The total score ranges from 0 to 54, with higher scores indicating more severe depressive symptoms. The scale demonstrated a Cronbach's alpha coefficient of 0.90 in our study.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAnxiety symptoms over the past two weeks were assessed by the Generalized Anxiety Disorder-7 (GAD-7) [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The GAD-7 is widely utilized for assessing anxiety symptoms. It consists of 7 items with a total score range of 0 to 21. Scoring involves assigning values of 0, 1, 2, and 3 to the response categories \"not at all,\" \"several days,\" \"more than half the days,\" and \"nearly every day,\" respectively. The scale exhibited a Cronbach's alpha coefficient of 0.93\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eMediators\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eFeelings of loneliness were assessed by the 3-Item UCLA Loneliness Scale (UCLA) [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. The UCLA is a validated instrument to assess feelings of loneliness, including items of relational connectedness, social connectedness, and self-perceived isolation. The items were rated from 1 to 3 (1\u0026thinsp;=\u0026thinsp;hardly ever, 2\u0026thinsp;=\u0026thinsp;some of the time, 3\u0026thinsp;=\u0026thinsp;often), and the total score ranged from 3 to 9, with higher scores indicative of heightened perceived loneliness.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003ePhysical activity (PA) was assessed by the frequency of physical exercise per week, and the index of the International Physical Activity Questionnaire - Short Form (IPAQ-SF) [\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The former did not include exercise during physical education (PE) lessons, while the latter did. The IPAQ-SF provided the sum of days and minutes spent engaging in vigorous PA, moderate PA, and walking. The index for each PA modality using metabolic equivalent minutes per week (MET-minutes/week) was calculated as: MET-level \u0026times; min of activity/day \u0026times; days/week. The calculation was conducted thrice, yielding separate MET-minutes/week for each modality (walking\u0026thinsp;=\u0026thinsp;3.3 METs, moderate PA\u0026thinsp;=\u0026thinsp;4.0 METs, vigorous PA\u0026thinsp;=\u0026thinsp;8.0 METs). The sum of these produced total MET-min/week for each student in the sample, with higher scores indicative of longer time and more intense exercise.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eSleep was measured by the Pittsburgh Sleep Quality Index (PSQI) [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The PSQI comprises 19 items and can be divided into seven components, including duration of sleep, sleep disturbance, sleep latency, day dysfunction due to sleepiness, sleep efficiency, overall sleep quality, and use of sleep medication. Each component is scored on a scale of 0 to 3, with the cumulative score across components yielding the total PSQI score. Higher scores indicate poorer sleep quality.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003eCovariates\u003c/h2\u003e \u003cp\u003eAll covariates were based on data at T1. Sociodemographic characteristics included age (years at T1, continuous), gender (female, male), school (public school, non-public school), family economic status (high, middle, low), parents' marital status (married, others), parents' education (primary school or lower, middle school, high school, college or higher) and relationship with parents (good, normal or poor). The selection of covariates was based on past literature documenting their associations with adolescent educational burden, mental health problems and mediators.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eFor each participant, we included data on two academic burden exposures (study time and academic stress, measured at each participant\u0026rsquo;s first wave T1), three latent mediators (loneliness, physical activity and sleep, measured at each participant\u0026rsquo;s second wave T2), and two outcomes (depression and anxiety, measured at each participant\u0026rsquo;s final wave T3). We also included confounders related to the mediators and outcomes (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of variables\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariables\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDetails of variables\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eAcademic burden relevant variables (measured at T1)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStudy time\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThe total hours of activities(time spent on homework assigned by school teachers, time spent on homework assigned by parents and off-campus tutors, and time spent on off-campus tutoring related to school subjects)per week.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAcademic stress\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eScores of ESSA, where higher scores indicate higher academic stress.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMediators (measured at T2)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLoneliness\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLatent measure of loneliness using three items of UCLA (relational connectedness, social connectedness, and self-perceived isolation).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhysical activity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLatent measure of frequency of physical exercise per week (excluding exercise during PE lessons), and the index of IPAQ-SF (MET-minutes/week) (including exercise during PE lessons).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSleep\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLatent measure of sleep quality using seven components of PSQI (sleep duration, sleep disturbances, sleep latency, daytime dysfunction, sleep efficiency, sleep quality, and sleep medication).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMental health outcomes (measured at T3)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDepressive symptoms\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eScores of CDI, where higher scores indicate more severe depressive symptoms.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnxiety symptoms\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eScores of GAD-7, where higher scores indicate more severe anxiety symptoms.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCovariates\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eAge, sex, type of school, family economic status, parents' marital status, parents\u0026rsquo; education level, relationship with parents\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003eESSA \u003cb\u003eEducational Stress Scale for Adolescents\u003c/b\u003e; UCLA \u003cb\u003eUCLA Loneliness Scale\u003c/b\u003e; IPAQ-SF \u003cb\u003eInternational Physical Activity Questionnaire - Short Form\u003c/b\u003e; MET-minutes/week \u003cb\u003emetabolic equivalent minutes per week\u003c/b\u003e; PSQI \u003cb\u003ePittsburgh Sleep Quality Index\u003c/b\u003e; CDI \u003cb\u003eChildren\u0026rsquo;s Depression Inventory\u003c/b\u003e; GAD-7 \u003cb\u003eGeneralized Anxiety Disorder-7\u003c/b\u003e.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWe analyzed the distribution of all variables using mean, SD, frequency, and percentage. There were no missing data for the participants involved in the analyses as the Wenjuanxing platform automatically checked for missing values and reminded the participants before submission. In primary analyses, we modeled each of the mediators as continuous latent factors. Details of the factors used in the latent mediators, selected based on previous research[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan additionalcitationids=\"CR35\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], are provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eTo understand the associations between variables before testing the full structural model, we analyzed paths between exposures, mediators, and outcomes in separate regression models, controlling for age, sex, type of school, parents' marital status, family economic status, parents\u0026rsquo; education level, and relationship with parents. Statistical significance was set a priori at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 with no adjustment for multiplicity.\u003c/p\u003e \u003cp\u003eAll hypothesized mediators were included in the final model simultaneously. Multiple mediation was used in the primary analysis due to its greater convenience, precision, and parsimony compared to multiple single mediation models, and it may also help reduce parameter bias caused by omitted variables [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Results are presented as standardized regression coefficients from the structural equation modeling (SEM). The coefficients were interpreted with regard to direction, magnitude, and statistical significance. The extent of mediation was described as the percentage of the total effect of an exposure mediated by a specific indirect effect. Based on previous research [\u003cspan additionalcitationids=\"CR39\" citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], the academic burden was treated sequentially, with study time preceding academic stress. We specified a correlational, rather than a directional, association between loneliness and physical activity, and between loneliness and sleep due to insufficient evidence regarding their directionality [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Physical activity was allowed to influence sleep [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. The residual covariance between the two outcome variables is presented.\u003c/p\u003e \u003cp\u003eModel fit was assessed using root mean square error of approximation (RMSEA), standardized root mean square residual (sRMR), comparative fit index (CFI), and Tucker-Lewis index (TLI). RMSEA and sRMR values of 0.06 or less indicated a good fit, although values up to 0.08 were considered acceptable[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. For CFI and TLI, values greater than 0.95 reflected a good model fit. The structural equation modeling (SEM) was conducted using the lavaan package ver. 0.6\u0026ndash;16 in R version 4.3.1.\u003c/p\u003e \u003cp\u003eIn sensitivity analyses, we separately conducted three mediation models with the dimensions or items of each latent mediator added in a single structural equation model. For example, for the mediating role of loneliness, the three loneliness items were tested as mediators in one model. The models were similar to those in the primary analyses except for the mediating variables to evaluate how individual factors of each mediator affected results.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 2965 participants took part in all the three assessments from T1 to T3, who were included in the current analysis. Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e shows the flow of participants through each wave of the study. Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e presents the characteristics of participants in the final sample. The mean age of respondents was 15.2 years (SD 1.7), with 1423 (48.0%) being female at baseline (T1). Most of the participants were in public school (68.9%) and had middle or high family economic status (94.8%).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eCharacteristics of participants in the analysis sample\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVariables\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOverall\u003c/p\u003e\n \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;2,965)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVariables\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOverall\u003c/p\u003e\n \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;2,965)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eT1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRelationship with father\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAge, years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.2 (1.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGood\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2,292(77.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSex\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNormal/poor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e673(22.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFemale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1,423(48.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStudy time per week (homework and off-campus tutoring), hours\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.8 (17.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1,542(52.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAcademic stress\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e52.6 (11.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSchool\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eT2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePublic school\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2,044(68.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLoneliness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNon-public school\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e921(31.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRelational connectedness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5 (0.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eParents\u0026apos; marital status\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSocial connectedness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5 (0.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMarried\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2,678 (90.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSelf-perceived isolation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.5 (0.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOthers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e287 (9.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePhysical activity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0(2.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFamily economic status\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eFrequency of physical activity per week (excluding physical education classes)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.0(2.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHigh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e422(19.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMiddle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1,654(75.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLow\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e114 (5.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eWeekly physical activity, MET-minutes/week\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1,174.2(1,869.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFather\u0026rsquo;s education\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePrimary school or lower\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e357(12.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMiddle school\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1,181(39.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSleep duration\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5 (0.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHigh school\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e843(28.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSleep disturbances\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.7 (0.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCollege or higher\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e584(19.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSleep latency\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.9 (0.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMother\u0026rsquo;s education\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDaytime dysfunction\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0 (1.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePrimary school or lower\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e467(15.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSleep efficiency\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3 (0.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMiddle school\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1,137(38.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSleep quality\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.8 (0.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHigh school\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e789(26.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSleep medication\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1 (0.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCollege or higher\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e572(19.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eT3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRelationship with mother\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDepressive symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.1 (8.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGood\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2,518(84.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAnxiety symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.8 (4.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNormal/poor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e447(15.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003eData are mean (SD) or n (%) unless otherwise indicated. MET-minutes/week stands for metabolic equivalent minutes per week.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eUsing maximum likelihood estimation with 5000 bootstrapped iterations, the final full structural model exhibited good model fit (RMSEA 0.048, 95% CI 0.046\u0026ndash;0.050, sRMR 0.035, CFI 0.986, TLI 0.979).\u003c/p\u003e\n\u003cp\u003eIn the preliminary analysis (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e) and the final model (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e; Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e), more academic stress was directly associated with higher levels of perceived loneliness, less physical activity, worse sleep, and more severe depressive and anxiety symptoms. In the final model, pathways from academic stress to loneliness and subsequently to depressive symptoms (indirect effect 0.07, 95% CI 0.06 to 0.08, effect size 26.7%) and anxiety symptoms (indirect effect 0.03, 95% CI 0.02 to 0.03, effect size 20.8%) were observed. Moreover, physical activity mediated the effect of academic stress on depressive symptoms (indirect effect 0.01, 95% CI 0.002 to 0.01), accounting for 1.9% of the total effect of academic stress on depressive symptoms. However, physical activity did not significantly mediate the association between academic stress and anxiety symptoms. The hypothesized mediation pathways, proceeding from academic stress to sleep and ultimately to depressive symptoms (indirect effect 0.08, 95% CI 0.07 to 0.10) and anxiety symptoms (indirect effect 0.04, 95% CI 0.03 to 0.05), were empirically substantiated, with longitudinal mediation effect sizes of 30.8% and 34.4%, respectively.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAssociations between exposures, mediators and outcomes\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAssociations\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEffect\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003estudy time\u0026thinsp;\u0026gt;\u0026thinsp;loneliness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00, 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eacademic stress\u0026thinsp;\u0026gt;\u0026thinsp;loneliness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.03 (0.03, 0.03) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003estudy time\u0026thinsp;\u0026gt;\u0026thinsp;physical activity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00, 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eacademic stress\u0026thinsp;\u0026gt;\u0026thinsp;physical activity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.01 (-0.02, -0.01) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003estudy time\u0026thinsp;\u0026gt;\u0026thinsp;sleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00, 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eacademic stress\u0026thinsp;\u0026gt;\u0026thinsp;sleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.04 (0.03, 0.04) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003estudy time\u0026thinsp;\u0026gt;\u0026thinsp;depressive symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.02 (0.003, 0.03) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eacademic stress\u0026thinsp;\u0026gt;\u0026thinsp;depressive symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.27 (0.24, 0.29) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eloneliness\u0026thinsp;\u0026gt;\u0026thinsp;depressive symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.42 (4.15, 4.69) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ephysical activity\u0026thinsp;\u0026gt;\u0026thinsp;depressive symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.25 (-2.48, 1.99)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esleep\u0026thinsp;\u0026gt;\u0026thinsp;depressive symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.44 (4.16, 4.72) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003estudy time\u0026thinsp;\u0026gt;\u0026thinsp;anxiety symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.01, 0.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eacademic stress\u0026thinsp;\u0026gt;\u0026thinsp;anxiety symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.13 (0.11, 0.14) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eloneliness\u0026thinsp;\u0026gt;\u0026thinsp;anxiety symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.82 (1.67, 1.97) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ephysical activity\u0026thinsp;\u0026gt;\u0026thinsp;anxiety symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.10 (-0.99, 0.80)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esleep\u0026thinsp;\u0026gt;\u0026thinsp;anxiety symptoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.03 (1.88, 2.19) \u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\"\u003e\u0026gt; indicates the direction of the regression path, i.e. study time predicts loneliness.\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\"\u003e\u003csup\u003e*\u003c/sup\u003e p value\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eStandardized regression coefficients for the direct and indirect effects for the final full structural model\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAcademic stress\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLoneliness\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePhysical activity\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSleep\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDepressive symptoms\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAnxiety symptoms\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMediators\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLoneliness (direct effect)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e2.49 (2.17 to 2.79)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.90 (0.71 to 1.09)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePhysical activity (direct effect)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-0.12 (-0.17 to -0.06)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-0.45 (-0.74 to -0.17)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.02 (-0.14 to 0.18)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIndirect effect via sleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-0.26 (-0.38 to -0.14)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-0.13 (-0.20 to -0.07)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSleep (direct effect)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e2.23 (1.91 to 2.55)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e1.16 (0.94 to 1.37)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAcademic stress\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDirect effect\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.03 (0.03 to 0.03)\u003c/strong\u003e \u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-0.01 (-0.02 to -0.01)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.04 (0.03 to 0.04)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.11 (0.08 to 0.13)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.06 (0.04 to 0.07)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal indirect effects\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.16 (0.14 to 0.18)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.07 (0.06 to 0.08)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia loneliness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.07 (0.06 to 0.08)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.03 (0.02 to 0.03)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia physical activity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.001 (0.001 to 0.002)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.01 (0.002 to 0.01)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia sleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.08 (0.07 to 0.10)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.04 (0.03 to 0.05)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia physical activity, and sleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.003 (0.001 to 0.01)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.001 (0.001 to 0.002)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal effect\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.27 (0.24 to 0.29)\u003c/strong\u003e \u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.13 (0.11 to 0.14)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eStudy time\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDirect effect\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.11 (0.08 to 0.13)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.01 (-0.00 to 0.03)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.00 (-0.01 to 0.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal indirect effects\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.01 to 0.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.01 to 0.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia loneliness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia physical activity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia sleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.01 to 0.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia physical activity, and sleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00 (-0.00 to 0.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVia academic stress\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.003 (0.002 to 0.004)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-0.001 (-0.002 to -0.001)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.004 (0.003 to 0.01)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.01 (0.01 to 0.02)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.01 (0.004 to 0.01)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal effect\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.02 (0.001 to 0.03)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.00 (-0.01 to 0.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eCovariances\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLoneliness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e-0.12 (-0.17 to -0.07)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.44 (0.39 to 0.48)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDepressive symptom\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e10.56 (9.33 to 11.72)\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e*\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\"\u003e\u003csup\u003e*\u003c/sup\u003e p value\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eIn the preliminary analysis (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e), longer study time was directly associated with more severe depressive symptoms, whereas in the final model, the results showed no significant direct effect of study time on any outcomes or mediators (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e; Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). However, longer study time had a positive effect on academic stress (\u0026beta;\u0026thinsp;=\u0026thinsp;0.11, 95% CI 0.08 to 0.13) and indirect effects via academic stress on loneliness, physical activity, sleep, depressive symptoms, and anxiety symptoms.\u003c/p\u003e\n\u003cp\u003eGreater loneliness was associated with more severe depressive symptoms (\u0026beta;\u0026thinsp;=\u0026thinsp;2.49, 95% CI 2.17 to 2.79) and anxiety symptoms (\u0026beta;\u0026thinsp;=\u0026thinsp;0.90, 95% CI 0.71 to 1.09) (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e; Table \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Loneliness was correlated with physical activity (\u0026beta;=-0.12, 95% CI -0.17 to -0.07) and sleep (\u0026beta;\u0026thinsp;=\u0026thinsp;0.44, 95% CI 0.39 to 0.48) in the final model. Physical activity had direct effect on depressive symptoms (\u0026beta;=-0.45, 95% CI -0.74 to -0.17) but not anxiety symptoms. More physical activity was associated with better sleep (\u0026beta;=-0.12, 95% CI -0.17 to -0.06). Sleep had direct effects on depressive symptoms (\u0026beta;\u0026thinsp;=\u0026thinsp;2.23, 95% CI 1.91 to 2.55) and anxiety symptoms (\u0026beta;\u0026thinsp;=\u0026thinsp;1.16, 95% CI 0.94 to 1.37).\u003c/p\u003e\n\u003cp\u003eIn our sensitivity analyses, the results from the single mediator models were largely consistent with the final model estimates (Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). All the three items of loneliness measure (relational connectedness, social connectedness, and self-perceived isolation) mediated the effects of academic stress on depressive and anxiety symptoms (Figure S2). Frequency of physical exercise excluding PE lessons mediated the impact of academic stress on depressive and anxiety symptoms, but weekly physical activity level including PE lessons (IPAQ-SF) did not (Figure S3). Academic stress had indirect effects via sleep duration, sleep disturbances, sleep latency, daytime dysfunction, and sleep quality on depressive symptoms, while via sleep duration, sleep disturbances, sleep latency, and daytime dysfunction on anxiety symptoms (Figure S4). The effect sizes for the pathways through daytime dysfunction and sleep disturbances were larger than the other dimensions of sleep (Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). The association between study time and depressive symptoms was not mediated by loneliness, physical activity and sleep.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur study conducted a comprehensive investigation into the longitudinal association between academic burden and symptoms of depression and anxiety and potential mediating pathways among middle and high school students in Taizhou, China. The results of this study indicated that higher academic stress was associated with more severe depressive and anxiety symptoms. Sleep, loneliness and physical activity mediated the association between academic stress and depressive symptoms, accounting for 30.8%, 26.7% and 1.9% of the total effect of academic stress respectively. Sleep and loneliness also mediated the association between academic stress and anxiety symptoms, with longitudinal mediation effect sizes of 34.4% and 20.8%, respectively. Study time was only associated with the outcomes indirectly via academic stress, reflecting that educational stress is likely to be more relevant to emotional problems than actual study time.\u003c/p\u003e \u003cp\u003eIn both preliminary analysis and structural model, we observed the mediating role of sleep in the associations between academic stress and symptoms of depression and anxiety, underscoring the importance of adequate and high-quality sleep for psychological well-being. Multiple factors contribute to the results. On the one hand, academic stress may influence sleep quality from biological aspects. Research by Adam et al. suggested that academic stress can disrupt an individual's biological clock, consequently affecting sleep quality[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. According to psychobiological models, academic stress, often marked by worry and rumination, may be related to mental hyperarousal which is a key factor for insomnia[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. On the other hand, the impact of sleep on symptoms of depression and anxiety aligns with findings from existing literature. A meta-analytic evaluation of longitudinal studies found that non-depressed individuals with insomnia had a twofold risk of developing depression compared to those with no sleep difficulties[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. Similarly, insomnia was found to be a major predictor for the onset of anxiety in a meta-analysis[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Although psychophysiological mechanisams for the associations are still not clear, researchers suggested that the impairment of sleep-wake regulating neural circuitries may result in changes in emotional reactivity[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. Moreover, in our sensitivity analyses, several domains of sleep, particularly in the realms of daytime dysfunction and sleep disturbances, were significant mediators of the associations between academic stress and emotional problems. They may be red flags to target for preventing depression and anxiety among adolescents in future studies.\u003c/p\u003e \u003cp\u003eLoneliness mediated the association between academic stress and symptoms of depression and anxiety, accounting for over 20% of the total effect of academic stress. This suggests that people with higher academic stress had more severe emotional problems in part because they had greater loneliness. Several factors may contribute to the observed associations. Academic stress, such as worrying a lot about exams, future education and employment, and being punished by teachers and parents, is inherent aspects of the educational environment in China [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Educational expectations are one of the main sources of stress in adolescents, and those with poor academic performance are more likely to have weak social connectedness and feel lonely [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. Students experiencing high levels of academic stress may withdraw from social interactions or perceive a lack of support from peers and teachers, contributing to increased feelings of loneliness\u003csup\u003e3\u003c/sup\u003e. Additionally, previous studies indicate a close association between feelings of loneliness and symptoms of depression and anxiety. Individuals experiencing loneliness are more prone to exhibit symptoms of depression such as low mood, loss of interest, and self-deprecation [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. Loneliness is also closely associated with symptoms of anxiety, including worries about the future, social anxiety, and doubts about one's own abilities [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. Our study extends beyond previous research and found that students who perceived deficits in social connections or experienced feelings of isolation were more vulnerable to the negative effects of academic stress on mental health. The results are consistent with a study in healthcare students and early-career professionals which reported that loneliness mediated the adverse impact of psychological stress on depressive and anxiety symptomatology during COVID-19 [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNoteworthy, the mediating role of physical activity in the association between academic stress and mental health outcomes is complex. We found a significant association between reduced physical activity and more severe depressive symptoms but not with anxiety symptoms. Consistent with previous studies, the risk of depression may be reduced by physical activity [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. A meta-analysis found that if the current physical activity recommendations had been achieved by less active individuals, 11.5% of depression cases could have been prevented [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Increased physical activity may alleviate depressive symptoms through the release of neurotransmitters such as dopamine and endorphins [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. However, there is a lack of significant association between physical activity and anxiety symptoms in our study. The result is consistent with a review which reported that vigorous exercise led to diminished depressive symptoms with no impact on anxiety among adolescents when compared to no intervention [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Although physical activity mediated the association between academic stress and depressive symptoms, the effect size for the pathway was smaller than those for the other two mediators, indicating that sleep and loneliness may play a more important role in the relationship. In further analysis, we found that frequency of physical exercise per week not including PE lessons mediated the association between academic stress and depressive and anxiety symptoms. However, academic stress did not significantly affect the outcomes via total MET-min per week which included exercise during PE lessons. Academic stress might reduce leisure physical activity but had less impact on the total intensity of exercise since PE lesson is a compulsory subject in school. Additionally, despite the potential benefits of physical activity, students may experience less pleasure through doing exercise when it becomes a task and relates to their scores at school [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]. In a systematic review, leasure-time physical activity was found to be the most effective domain for improving mental health, while occupational or domestic physical activity was related to worse mental health outcomes [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWe observed that study time did not have a significant direct impact on the mediators or outcomes, but it exerted an influence through academic stress. Students who spend longer hours studying often experience higher academic stress. The study time we measured contained time spent on homework assigned by school teachers, parents and off-campus tutors, and time spent on off-campus tutoring related to school subjects. When the information and tasks placed on working memory exceed its capacity, cognitive overload can occur, which often triggers the stress response [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. Multiple tasks at the same time can generate a feeling of lack of time to finish homework or to have a good performance. In addition, the additional learning tasks assigned by parents and off-campus tutors reduce the time available for relaxation and social activities, and may impair a sense of choice in adolescents with respect to their behavior, which in turn increase academic stress. Study time had a weaker effect on the outcomes, reflecting that academic stress may be better than study time for differentiating between adolescents with different levels of academic burden and may be a stronger predictor of mental health problems than measures of objective workload.\u003c/p\u003e \u003cp\u003eStrengths of this study are three waves of longitudinal data, test of multiple competing hypotheses, and use of validated scales. While there is consistent evidence that adolescents with greater academic burden are more likely to experience emotional problems [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e], a notable gap exists in empirically investigating factors mediating the associations. Importantly, our evaluation of potential mediators sheds light on the role of sleep, loneliness and physical activity in driving the associations. This research fills the gap in the literature and provides information for the development of targeted interventions aimed at mitigating the adverse effects of academic burden on mental health of adolescents.\u003c/p\u003e \u003cp\u003eIn spite of these advantages, we should acknowledge several limitations. Firstly, our research was conducted in the specific cultural and educational settings, which may not fully represent the experiences of adolescents in other regions or cultural environment. Secondly, although validated measures were used to evaluate academic stress, meditators and mental health outcomes, potential response bias and self-report bias might still exist. Thirdly, the pandemic might have some impact on the results. However, our study was conducted during a relatively stable period of the pandemic and schools in Taizhou were reopened before the start of the survey at T1, and thus we did not suppose the effect to be profound. Finally, while factors including loneliness, physical activity, and sleep quality have been identified as mediators influencing the association between academic stress and emotional disturbances, the relationships between study time and mental health problems remain incompletely understood. Further research designed to measure other potentially modifiable factors on the pathway from actual study burden to emotional and behavioral problems should be investigated.\u003c/p\u003e \u003cp\u003eOur study have practical implications for guiding educational policies, intervention development and school management practices for adolescents, especially those in a highly competitive educational environment. Given the association between academic stress and depressive and anxiety symptoms, schools should strengthen psychological health education and provide psychological support services to help students effectively manage stress and promote mental well-being. Our findings also underscore the responsibility of educational policymakers to carry out reforms to reduce students' academic pressure. This may include reassessing curriculum loads and devising more flexible learning schedules to ensure that students' academic burden is not excessively heavy. More educational burden reduction programs should be designed and implemented, such as the Double Reduction campaign in China aiming at reducing heavy workloads and excessive off-campus tutoring for students [\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]. Moreover, our study found key mediators which could be important targets for intervention, including sleep, loneliness and physical activity. Parents and school administrators should strengthen collaboration and offer guidance on sleep management to ensure that students obtain sufficient and high-quality sleep and reduce daytime dysfunction. More social support and opportunities for social activities should also be provided to enhance social connectedness and reduce loneliness. Apart from exercise during PE lessons, parents and teachers can encourage students to engage in leisure-time exercise by themselves as it is the domain of physical activity most associated with mental health [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]. By recognizing and addressing the impact of academic burden on mental health, policymakers, educators and parents can work together to create a suitable educational environment which lays foundation for adolescents\u0026rsquo; long-term success and happiness.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, this study found that poorer sleep, higher loneliness and less physical activity experienced by adolescents with greater academic burden gave rise to emotional problems. Our results contribute to a deeper understanding of the complex pathways linking academic burden and mental health outcomes among adolescents. The findings underscore the importance of addressing academic burden and provide valuable insights for the development of comprehensive interventions to protect students' mental well-being. Apart from direct strategies to reduce study time and alleviate academic stress, effective interventions to deal with mediating factors, such as ensuring high-quality sleep, mitigating loneliness and stimulating voluntary physical activities in leisure time, are also beneficial to adolescent mental health.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eSEM \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Structural equation modeling\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRMSEA \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Root mean square error of approximation\u003c/p\u003e\n\u003cp\u003esRMR \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Standardized root mean square residual\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCFI \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Comparative fit index\u003c/p\u003e\n\u003cp\u003eTLI \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Tucker-Lewis index\u003c/p\u003e\n\u003cp\u003eESSA \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Educational Stress Scale for Adolescents\u003c/p\u003e\n\u003cp\u003eUCLA \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; UCLA Loneliness Scale\u003c/p\u003e\n\u003cp\u003eIPAQ-SF \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; International Physical Activity Questionnaire - Short Form\u003c/p\u003e\n\u003cp\u003eMET-minutes/week \u0026nbsp; \u0026nbsp;Metabolic equivalent minutes per week\u003c/p\u003e\n\u003cp\u003ePSQI \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Pittsburgh Sleep Quality Index\u003c/p\u003e\n\u003cp\u003eCDI \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Children\u0026rsquo;s Depression Inventory\u003c/p\u003e\n\u003cp\u003eGAD-7 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Generalized Anxiety Disorder-7\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eEthics approval and consent to participate\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was approved by the Ethics Committee of Taizhou Central Hospital (2022L-01-17), and all methods were carried out in accordance with relevant guidelines and regulations. All participants and parents or legal guardians of the children participating in our study provided informed consent prior to study participation. Informed consent procedures were used to collect all study data.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eConsent for publication\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors approved the final manuscript for publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAvailability of data and materials\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eCompeting interests\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFunding\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJW was sponsored by the China Medical Board (grant number #22-472) and the National Natural Science Foundation of China (grant number 72104053). CF was sponsored by the General Project of Shanghai Municipal Health Commission (grant number 202240115). HL and XC were sponsored by the Special Support Program for High Level Talents in Taizhou (grant number TZ2022-2). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAuthors\u0026apos; contributions\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJW, XC, and CF designed the study and formulated the outline and structure of the article. JW, ZW, and YY conducted data collection and analysis, as well as drafted the manuscript. TW, HL and WZ interpreted the results and critically reviewed the manuscript. XC and CF reviewed the manuscript. All authors align with the the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAcknowledgements\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe express our heartful gratitude to the study participants for their invaluable contributions. We also sincerely appreciate the dedication and hard work of the Taizhou City Center for Disease Prevention and Control (CDC) and the local CDCs.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAdolescent mental health statistics. In: UNICEF DATA. https://data.unicef.org/topic/child-health/mental-health/. Accessed 6 Dec 2023\u003c/li\u003e\n\u003cli\u003eWang C, Zhang P, Zhang N. Adolescent mental health in China requires more attention. The Lancet Public health 5:e637\u0026ndash;e637\u003c/li\u003e\n\u003cli\u003eADOLESCENT MENTAL HEALTH | UNICEF China. https://www.unicef.cn/en/reports/adolescent-mental-health. 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A longitudinal examination of the relation between academic stress and anxiety symptoms among adolescents in India: The role of physiological hyperarousal and social acceptance. Int J Psychol 57:401\u0026ndash;410\u003c/li\u003e\n\u003cli\u003eLiu S, Chen YN. Perceived stress and problematic smartphone use in Chinese college students:Loneliness as a mediator and gender as a moderator. Psychological Research. 2020;13(6):551-558. (in Chinese)\u003c/li\u003e\n\u003cli\u003eDm C. Stress and perceived social isolation (loneliness). Archives of gerontology and geriatrics. https://doi.org/10.1016/j.archger.2019.02.007\u003c/li\u003e\n\u003cli\u003eMcIntyre JC, Worsley J, Corcoran R, Harrison Woods P, Bentall RP. Academic and non-academic predictors of student psychological distress: the role of social identity and loneliness. Journal of mental health (Abingdon, England) 27:230\u0026ndash;239\u003c/li\u003e\n\u003cli\u003eWunsch K, Fiedler J, Bachert P, Woll A. 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Insomnia as a predictor of depression: A meta-analytic evaluation of longitudinal epidemiological studies. Journal of affective disorders 135:10\u0026ndash;19\u003c/li\u003e\n\u003cli\u003eChellappa SL, Aeschbach D. Sleep and anxiety: From mechanisms to interventions. Sleep Med Rev 61:101583\u003c/li\u003e\n\u003cli\u003eSun J, Dunne MP, Hou X, Xu A. Educational Stress Scale for Adolescents: Development, Validity, and Reliability With Chinese Students. Journal of Psychoeducational Assessment 29:534\u0026ndash;546\u003c/li\u003e\n\u003cli\u003eLima LS, Ribeiro GS, De Aquino SN, Volpe FM, Martelli DRB, Swerts MSO, Parana\u0026iacute;ba LMR, Martelli J\u0026uacute;nior H. Prevalence of depressive symptoms in patients with cleft lip and palate. Brazilian Journal of Otorhinolaryngology 81:177\u0026ndash;183\u003c/li\u003e\n\u003cli\u003eKovacs M. The Children\u0026rsquo;s Depression, Inventory (CDI). Psychopharmacology bulletin 21:995-\u003c/li\u003e\n\u003cli\u003eBento C, Pereira AT, Marques M, Saraiva J, Macedo A. 1765 \u0026ndash; Futher validation of the children\u0026rsquo;s depression inventory in a portuguese adolescents sample. European psychiatry 28:1\u0026ndash;1\u003c/li\u003e\n\u003cli\u003eRobert L. Spitzer, MD; Kurt Kroenke, MD; Janet B. W. Williams, DSW; Bernd L\u0026ouml;we, MD, PhD. A brief measure for assessing generalized anxiety disorder. Arch Intern Med 166:1092\u0026ndash;1097\u003c/li\u003e\n\u003cli\u003eHughes ME, Waite LJ, Hawkley LC, Cacioppo JT. A Short Scale for Measuring Loneliness in Large Surveys: Results From Two Population-Based Studies. Res Aging 26:655\u0026ndash;672\u003c/li\u003e\n\u003cli\u003eMullen RA, Tong S, Sabo RT, Liaw WR, Marshall J, Nease DE, Krist AH, Frey JJ. Loneliness in Primary Care Patients: A Prevalence Study. Ann Fam Med 17:108\u0026ndash;115\u003c/li\u003e\n\u003cli\u003eWarnimont SC. International Physical Activity Questionnaire. Critical reviews in physical and rehabilitation medicine 30:\u003c/li\u003e\n\u003cli\u003eYu H, Zhu W, Qiu J. International Physical Activity Questionnaire (IPAQ-SF) for Chinese College Students: A Validation Study. Medicine \u0026amp; Science in Sports \u0026amp; Exercise 49:476\u003c/li\u003e\n\u003cli\u003eCRAIG CL, MARSHALL AL, SJ??STR??M M, et al. International Physical Activity Questionnaire: 12-Country Reliability and Validity. Medicine and science in sports and exercise 35:1381\u0026ndash;1395\u003c/li\u003e\n\u003cli\u003eWang C, Chen P, Zhuang J. Validity and Reliability of International Physical Activity Questionnaire-Short Form in Chinese Youth. Research quarterly for exercise and sport 84:S80\u0026ndash;S86\u003c/li\u003e\n\u003cli\u003eMollayeva T, Thurairajah P, Burton K, Mollayeva S, Shapiro CM, Colantonio A. The Pittsburgh sleep quality index as a screening tool for sleep dysfunction in clinical and non-clinical samples: A systematic review and meta-analysis. Sleep medicine reviews 25:52\u0026ndash;73\u003c/li\u003e\n\u003cli\u003ePreacher KJ, Hayes AF. Asymptotic and resampling strategies for assessing and comparing indirect effects in multiple mediator models | Behavior Research Methods. Behavior research methods 2008/08/01 2008:879\u0026ndash;891\u003c/li\u003e\n\u003cli\u003eChyu EPY, Chen J-K. The Correlates of Academic Stress in Hong Kong. Int J Environ Res Public Health 19:4009\u003c/li\u003e\n\u003cli\u003eTuominen-Soini H, Salmela-Aro K. Schoolwork Engagement and Burnout Among Finnish High School Students and Young Adults: Profiles, Progressions, and Educational Outcomes. Developmental psychology 50:649\u0026ndash;662\u003c/li\u003e\n\u003cli\u003eBergmann C, Muth T, Loerbroks A. Medical students\u0026rsquo; perceptions of stress due to academic studies and its interrelationships with other domains of life: a qualitative study. Medical education online 24:1603526\u0026ndash;1603526\u003c/li\u003e\n\u003cli\u003eGriffin SC, Williams AB, Ravyts SG, Mladen SN, Rybarczyk BD. Loneliness and sleep: A systematic review and meta-analysis. Health Psychol Open 7:2055102920913235\u003c/li\u003e\n\u003cli\u003ePels F, Kleinert J. Loneliness and physical activity: A systematic review. International Review of Sport and Exercise Psychology 9:231\u0026ndash;260\u003c/li\u003e\n\u003cli\u003eDolezal BA, Neufeld EV, Boland DM, Martin JL, Cooper CB. Interrelationship between Sleep and Exercise: A Systematic Review. Adv Prev Med 2017:1364387\u003c/li\u003e\n\u003cli\u003eHoyle RH, Panter AT. Writing about Structural Equation Models. Structural equation modeling: Concepts, issues, and applications Sage Publications, Inc:158\u0026ndash;176\u003c/li\u003e\n\u003cli\u003eAdam EK, Snell EK, Pendry P. Sleep timing and quantity in ecological and family context: a nationally representative time-diary study. J Fam Psychol 21:4\u0026ndash;19\u003c/li\u003e\n\u003cli\u003eRiemann D, Nissen C, Palagini L, Otte A, Perlis ML, Spiegelhalder K. The neurobiology, investigation, and treatment of chronic insomnia. Lancet Neurol 14:547\u0026ndash;558\u003c/li\u003e\n\u003cli\u003eBaglioni C, Battagliese G, Feige B, Spiegelhalder K, Nissen C, Voderholzer U, Lombardo C, Riemann D. Insomnia as a predictor of depression: a meta-analytic evaluation of longitudinal epidemiological studies. J Affect Disord 135:10\u0026ndash;19\u003c/li\u003e\n\u003cli\u003eHertenstein E, Feige B, Gmeiner T, et al. Insomnia as a predictor of mental disorders: A systematic review and meta-analysis. Sleep Med Rev 43:96\u0026ndash;105\u003c/li\u003e\n\u003cli\u003eRiemann D, Spiegelhalder K, Feige B, Voderholzer U, Berger M, Perlis M, Nissen C. The hyperarousal model of insomnia: a review of the concept and its evidence. Sleep Med Rev 14:19\u0026ndash;31\u003c/li\u003e\n\u003cli\u003eLan Z, Liu H, Huang X, Wang Q, Deng F, Li J. The Impact of Academic Pressure and Peer Support on Adolescents\u0026rsquo; Loneliness: A Polynomial Regression and Response Surface Analysis. Psychol Res Behav Manag 16:4617\u0026ndash;4627\u003c/li\u003e\n\u003cli\u003eHeinrich LM, Gullone E. The clinical significance of loneliness: a literature review. Clin Psychol Rev 26:695\u0026ndash;718\u003c/li\u003e\n\u003cli\u003eCacioppo JT, Hawkley LC. Perceived social isolation and cognition. Trends Cogn Sci 13:447\u0026ndash;454\u003c/li\u003e\n\u003cli\u003eHawkley LC, Cacioppo JT. Loneliness matters: a theoretical and empirical review of consequences and mechanisms. Ann Behav Med 40:218\u0026ndash;227\u003c/li\u003e\n\u003cli\u003eMatthews T, Danese A, Wertz J, Odgers CL, Ambler A, Moffitt TE, Arseneault L. Social isolation, loneliness and depression in young adulthood: a behavioural genetic analysis. Soc Psychiatry Psychiatr Epidemiol 51:339\u0026ndash;348\u003c/li\u003e\n\u003cli\u003eBonilla-Sierra P, Manrique-G A, Hidalgo-Andrade P, Ruisoto P. Psychological Inflexibility and Loneliness Mediate the Impact of Stress on Anxiety and Depression Symptoms in Healthcare Students and Early-Career Professionals During COVID-19. Front Psychol 12:729171\u003c/li\u003e\n\u003cli\u003ePearce M, Garcia L, Abbas A, et al. Association Between Physical Activity and Risk of Depression: A Systematic Review and Meta-analysis. JAMA Psychiatry 79:550\u0026ndash;559\u003c/li\u003e\n\u003cli\u003eHeissel A, Heinen D, Brokmeier LL, et al. Exercise as medicine for depressive symptoms? A systematic review and meta-analysis with meta-regression. Br J Sports Med 57:1049\u0026ndash;1057\u003c/li\u003e\n\u003cli\u003ePenedo FJ, Dahn JR. Exercise and well-being: a review of mental and physical health benefits associated with physical activity. Curr Opin Psychiatry 18:189\u0026ndash;193\u003c/li\u003e\n\u003cli\u003eRichards J, Jiang X, Kelly P, Chau J, Bauman A, Ding D. Don\u0026rsquo;t worry, be happy: cross-sectional associations between physical activity and happiness in 15 European countries. BMC Public Health 15:53\u003c/li\u003e\n\u003cli\u003eTeno SC, Silva MN, J\u0026uacute;dice PB. Physical activity and sedentary behaviour-specific domains and their associations with mental health in adults: a systematic review. Advances in Mental Health 0:1\u0026ndash;28\u003c/li\u003e\n\u003cli\u003eBodys-Cupak I, Grochowska A, Zalewska-Puchaa J, Majda A. Stress and coping strategies of medical students during their first clinical practice \u0026ndash; a pilot study. Medical Studies 35:294\u0026ndash;303\u003c/li\u003e\n\u003cli\u003eXu J, Wang H, Liu S, Hale ME, Weng X, Ahemaitijiang N, Hu Y, Suveg C, Han ZR. Relations among family, peer, and academic stress and adjustment in Chinese adolescents: A daily diary analysis. Developmental psychology 59:1346\u0026ndash;1358\u003c/li\u003e\n\u003cli\u003eThe General Office of the CPC Central Committee and the General Office of the State Council. The opinions on easing the burden of excessive homework and off-campus tutoring for students undergoing compulsory education. Beijing: Ministry of Education of the People\u0026apos;s Republic of China.http://www.moe.gov.cn/jyb_xxgk/moe_1777/moe_1778/202107/t20210724_546576.html. Accessed 10 May 2024 (in Chinese)\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Academic burden, Adolescence, Mental health, Depression, Anxiety, Loneliness, Physical activity, Sleep","lastPublishedDoi":"10.21203/rs.3.rs-4435974/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4435974/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eThere is a high prevalence of depression and anxiety in adolescents, and emotional problems are more likely to occur for students with high academic burden. The reasons underlying the educational impact are not well understood. This study aimed to explore loneliness, physical activity, and sleep as potential mediating pathways between academic burden and emotional problems in adolescents.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA longitudinal cohort study was conducted among middle and high school students in Taizhou City, Zhejiang Province, China with data collected at three time points (T1: April-May 2022, T2: September-October 2022, T3: February-May 2023). Depressive and anxiety symptoms were assessed using the Children\u0026rsquo;s Depression Inventory and the Generalized Anxiety Disorder-7, respectively. Structural equation modeling was employed to analyze the direct effect of academic burden (measured by study time and academic stress) on depressive and anxiety symptoms, and the indirect effects of academic burden via three mediators: loneliness, physical activity, and sleep.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eUsing data from 2965 adolescents who completed all the three assessments, we found that higher academic stress at T1 was directly associated with more severe depressive symptoms at T3. Sleep (indirect effect 0.08, 95% CI 0.07 to 0.10), loneliness (0.07, 0.06 to 0.08) and physical activity (0.01, 0.002 to 0.01) mediated the association, accounting for 30.8%, 26.7% and 1.9% of the total effect of academic stress respectively. For anxiety symptoms, sleep (0.04, 0.03 to 0.05) and loneliness (0.03, 0.02 to 0.03) mediated the effect of academic stress with longitudinal mediation effect sizes of 34.4% and 20.8%, respectively. Study time was only associated with the outcomes indirectly via academic stress.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eOur findings suggest that sleep, loneliness and physical activity could partly explain why adolescents with higher academic stress had more severe emotional problems, highlighting the importance of behavior and psychosocial differences driven by academic burden in explaining severity of mental health problems. The findings should raise awareness about the related risk factors of academic burden for adolescents, and strengthen calls for comprehensive strategies to improve adolescent mental health.\u003c/p\u003e","manuscriptTitle":"Academic burden and emotional problems among adolescents in China: a longitudinal mediation analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-04 21:39:58","doi":"10.21203/rs.3.rs-4435974/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ea49ecec-5fb9-4e56-bc96-15e4d5412745","owner":[],"postedDate":"June 4th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-04T21:40:00+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-04 21:39:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4435974","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4435974","identity":"rs-4435974","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}