Maternal Vitamin D Use During Pregnancy and Infant Supplementation as Determinants of Serum 25(OH)D Levels in Children Aged 6–24 Months

Maternal Vitamin D Use During Pregnancy and Infant Supplementation as Determinants of Serum 25(OH)D Levels in Children Aged 6–24 Months | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Maternal Vitamin D Use During Pregnancy and Infant Supplementation as Determinants of Serum 25(OH)D Levels in Children Aged 6–24 Months Mert Temuçin, Atilla Çifci This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9097943/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The complementary feeding period is a critical stage for infant nutrition and vitamin D status. This study aimed to determine whether maternal vitamin D use during pregnancy and infant supplementation predict serum 25(OH)D levels in children aged 6–24 months. This analytical cross-sectional study included 267 mother–child pairs between November 2023 and February 2024. Sociodemographic characteristics, feeding practices, vitamin D supplementation habits, and serum 25(OH)D levels were collected. Group comparisons were performed using independent samples t-tests and one-way ANOVA, and predictors of serum 25(OH)D levels were assessed using multiple linear and multinomial logistic regression analyses. The mean age of the children was 13.5 ± 4.8 months. Regular vitamin D supplementation was reported in 67.0% of children, whereas 11.3% used supplementation irregularly and 21.7% received none. Vitamin D deficiency was detected in 20.6% of children and insufficiency in 10.5%. Children whose mothers used vitamin D during pregnancy had significantly higher serum 25(OH)D levels (p < 0.001). In the regression model, maternal vitamin D use during pregnancy, infant supplementation status, and vitamin D dose were significant predictors of serum 25(OH)D levels (R² = 0.346, p < 0.001). Maternal non-use of vitamin D during pregnancy increased the risk of vitamin D deficiency (OR = 15.27, 95% CI 5.82–40.02), and irregular supplementation was associated with markedly higher odds of deficiency (OR = 28.16, 95% CI 8.21–96.64). Conclusion : Maternal vitamin D use during pregnancy and regular infant supplementation are key determinants of optimal serum 25(OH)D levels in early childhood. Vitamin D infants supplementation complementary feeding 25(OH)D What is Known • Vitamin D deficiency remains common in infants despite national supplementation programs. • Maternal vitamin D status influences neonatal vitamin D levels. What is New • Maternal vitamin D use during pregnancy is a major determinant of infant serum 25(OH)D levels. • Irregular infant supplementation is associated with a markedly increased risk of vitamin D deficiency. Introduction Over the past decade, vitamin D deficiency has received increasing attention due to its effects not only on bone health but also on various chronic diseases, including diabetes, cancer, autoimmune disorders, and infections [ 1 – 3 ]. Vitamin D plays a crucial role in calcium and phosphorus homeostasis and is essential for normal bone mineralization and skeletal development [ 3 ]. Deficiency resulting from impaired bone mineralization presents as rickets in infants and young children and as osteomalacia in post-adolescent and adult populations (Charoenngam). Rickets is characterized by delayed closure of fontanelles, lower limb deformities, short stature, and growth retardation, although vitamin D deficiency may also occur without obvious clinical manifestations [ 4 , 5 ]. In national studies conducted in Turkey before vitamin D supplementation became a health policy priority, the prevalence of rickets among children aged 0–3 years ranged from 1.67% to 19% [ 6 ]. Globally, vitamin D deficiency is estimated to affect more than one billion people, with infants and young children representing one of the most vulnerable populations due to rapid growth and limited dietary vitamin D intake [ 7 ]. Due to limited dietary intake of vitamin D, insufficient sunlight exposure, and the lack of food fortification policies, deficiency and insufficiency are widely reported. Community-based studies report prevalence rates of approximately 15%, although some studies have reported rates as high as 90% [ 8 , 9 ]. Children aged 0–24 months, especially during the complementary feeding period (6–24 months), pregnant women, and elderly adults constitute high-risk groups [ 10 ]. This period is critical because the introduction of complementary foods alters dietary diversity and vitamin D intake. In addition, the transition to complementary feeding may influence adherence to vitamin D supplementation [ 11 ]. In response to these risks, the Turkish Ministry of Health launched the “Project for the Prevention of Vitamin D Deficiency and the Protection of Bone Health” in 2005 and provided free daily supplementation of 400 IU of vitamin D to infants from birth until one year of age [ 12 ]. Due to the absence of vitamin D–fortified foods in Turkey and the ongoing risk of rickets, continuation of vitamin D supplementation throughout the first three years of life is recommended [ 5 ]. Furthermore, adherence to vitamin D supplementation during the complementary feeding period may vary, emphasizing the importance of identifying factors that influence consistent intake, such as maternal vitamin D status, parental awareness, socioeconomic conditions, and guidance from healthcare providers [ 13 – 14 ]. Additionally, since 2011, the “Vitamin D Supplementation Program for Pregnant Women” has provided 1200 IU of vitamin D daily from the 12th week of gestation until six months postpartum [ 15 ]. Despite these initiatives, current studies indicate that one-third of children living in urban areas still experience vitamin D deficiency [ 16 – 18 ]. An additional concerning factor is maternal vitamin D deficiency, which directly affects the vitamin D levels of neonates, with reported deficiency rates among Turkish mothers ranging from 55% to 81% [ 19 ]. These observations underscore the importance of developing comprehensive strategies that target both maternal and infant vitamin D status, particularly during the complementary feeding period, as well as the continued training of healthcare professionals in supplementation management [ 15 , 20 ]. Despite national vitamin D supplementation programs in Turkey, vitamin D deficiency remains common among young children. However, limited research has examined how maternal vitamin D use, infant supplementation behaviors, and feeding practices jointly influence serum 25(OH)D levels during the complementary feeding period. This stage represents an important transition in infant nutrition, during which dietary patterns change and adherence to supplementation may decline. Understanding the factors associated with serum vitamin D status during this critical developmental window is essential for improving prevention strategies. Therefore, this study aimed to evaluate serum 25(OH)D levels and vitamin D supplementation practices in children aged 6–24 months and to identify maternal, supplementation-related, and feeding-related factors associated with vitamin D status. Methods Study Design This analytical cross-sectional study was conducted between October 1, 2023, and February 1, 2024, at the social pediatrics outpatient clinic of a tertiary state hospital in Türkiye. Children and their mothers who applied to the clinic and whose serum 25(OH)D levels were measured during routine examinations were included. Participants Exclusion criteria were as follows: children younger than 6 months or older than 24 months; a diagnosis of rickets; disorders of vitamin D absorption or metabolism; chronic diseases that could lead to vitamin D deficiency (e.g., epilepsy, celiac disease, inflammatory bowel disease, chronic liver disease, or chronic renal failure); and serum 25(OH)D levels above 100 ng/mL. Serum 25(OH)D concentrations were measured using a chemiluminescence immunoassay method in the hospital laboratory. An a priori sample size calculation was performed for multiple linear regression analysis using an effect size of 0.15, an alpha level of 0.05, a power of 0.80, and six predictors. The minimum required sample size was calculated as 98 participants [21]. Since 267 mother–child pairs were included in the study, the sample size was considered sufficient. During the study period, 300 children were approached for participation. Of these, 15 mothers declined to participate and 18 children were excluded due to insufficient or clotted blood samples. Consequently, the final study sample consisted of 267 children and their mothers. Instrument Data were collected using a Data Collection Form developed by the researcher. The form consisted of two sections: Sociodemographic information : child’s age, gender, gestational week, family type, number of siblings, parents’ employment status, mother’s age, and family income level. Vitamin D use-related questions : 25(OH)D level, child’s feeding type, maternal vitamin D intake during pregnancy, child’s vitamin D supplementation, type and dosage of the supplement, start time, the person who initiated supplementation, reasons for non-use, and current vitamin D status. As part of the pilot study, the form was administered to 10 children and their mothers to ensure clarity and feasibility. Serum 25(OH)D levels were measured and categorized according to the criteria proposed by Holick (2009) as deficiency (<20 ng/mL), insufficiency (21–29 ng/mL), and sufficient (≥30 ng/mL). Pilot participants were not included in the main sample [22]. The Data Collection Form was completed by the researcher during face-to-face interviews with the mothers. The data collection process took approximately 10 minutes per participant. During the pilot study, the questions were found to be understandable, so no modifications were needed before the main study. Statistical Analysis Statistical analyses were performed using IBM SPSS Statistics for Windows, Version 26.0 (IBM Corp., Armonk, NY, USA). Continuous variables were expressed as mean ± standard deviation (SD), and categorical variables were presented as numbers and percentages. Normality of continuous variables was assessed using the Shapiro–Wilk test and visual inspection of histograms. For normally distributed variables, independent samples t-tests were used to compare two groups, and one-way analysis of variance (ANOVA) was used to compare three or more groups. Significant ANOVA results were further examined using Tukey’s post-hoc test. Multiple linear regression analysis was conducted to identify independent predictors of serum 25(OH)D levels. Variables considered clinically relevant, including child age, maternal vitamin D use during pregnancy, infant vitamin D supplementation status, and vitamin D dose, were included in the model. Multicollinearity among independent variables was assessed using variance inflation factors (VIF). In addition, multinomial logistic regression analysis was performed to examine factors associated with vitamin D insufficiency and deficiency with normal vitamin D status as the reference category. Model fit was evaluated using likelihood ratio chi-square statistics and Nagelkerke R². Statistical significance was set at p < 0.05. Ethical Approval Ethical approval for the study was obtained from the Ankara Bilkent City Hospital Clinical Research Ethics Committee (Decision No: E2-23-5197, Date: 25.10.2023) and the Ankara Bilkent City Hospital Pediatric Hospital Specialty Training Academic Committee (Decision No: 16, Date: 11.09.2023). The study was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants. Results A total of 267 children were included in the study, and the sociodemographic and clinical characteristics of the participants are presented in Table 1. The mean age of the children was 13.5 ± 4.8 months, and 52.8% were girls. The majority of the children were born at ≥38 weeks of gestation (67.0%), and approximately half were only children (49.1%). In 53.2% of the families, only one parent was employed, and the majority of the mothers were between 21 and 35 years of age (85.0%). Characteristics related to feeding practices and vitamin D use are presented in Table 2. Examination of feeding practices showed that 48.3% of the children received mixed feeding (breast milk and complementary foods), 40.8% consumed family foods, and 10.9% were fed predominantly milk-based diets. It was determined that 80.9% of the mothers used vitamin D during pregnancy. Among the children, 67.0% used vitamin D supplementation regularly, 11.2% used it irregularly, and 21.7% did not use it at all. Evaluation of serum 25(OH)D levels showed that 68.9% of the children had normal levels, 10.5% had insufficient levels, and 20.6% had deficient levels. Serum 25(OH)D levels showed significant differences according to some sociodemographic characteristics (Table 1). In the analysis based on age groups, the serum 25(OH)D levels of children younger than 12 months were found to be significantly higher than those of children older than 18 months (F = 4.68, p = 0.011). Similarly, children born before 38 weeks of gestation had higher serum vitamin D levels than those born at ≥38 weeks (t = −2.05, p = 0.042). In addition, a significant difference in serum 25(OH)D levels was observed according to the number of siblings (F = 3.936, p = 0.026). However, no significant differences in serum vitamin D levels were found according to the child’s sex, parental employment status, mother’s age, or family income level (p > 0.05). In the analyses conducted according to feeding and supplementation characteristics (Table 2), it was found that the serum 25(OH)D levels of children whose mothers used vitamin D during pregnancy were significantly higher (t = 6.49, p < 0.001). In addition, a significant difference in serum 25(OH)D levels was observed according to the type of vitamin D preparation used (F = 18.9, p < 0.001). Post-hoc analysis showed that children who used vitamin D₃ drops had higher serum 25(OH)D levels than those who used multivitamins and those who did not receive supplementation. Similarly, children who used vitamin D supplementation regularly had significantly higher serum 25(OH)D levels than those who used it irregularly or not at all (F = 65.8, p < 0.001). Furthermore, children who received more than three drops of vitamin D per day had higher serum 25(OH)D levels than those who received three drops per day (t = −4.266, p < 0.001). A multiple linear regression analysis was performed to evaluate the independent predictors associated with serum 25(OH)D levels (Table 3). The constructed multiple linear regression model was found to be statistically significant (F(6,260) = 22.9, p < 0.001) and explained 34.6% of the variance in serum 25(OH)D levels (R² = 0.346; adjusted R² = 0.331). According to the analysis results, maternal non-use of vitamin D during pregnancy was associated with significantly lower serum 25(OH)D levels in children (B = −22.521, p < 0.001). Similarly, irregular use of vitamin D supplementation (B = −30.522, p < 0.001) or no supplementation (B = −16.657, p = 0.014) in infants was associated with lower serum 25(OH)D levels compared with regular supplementation. In contrast, receiving more than three drops of vitamin D per day was associated with higher serum 25(OH)D levels compared with receiving three drops per day (B = 15.619, p = 0.002). A multinomial logistic regression analysis was performed to examine the factors associated with vitamin D insufficiency and deficiency (Table 4). The constructed multinomial logistic regression model was found to be statistically significant (Likelihood ratio χ²(16) = 116, p < 0.001) and explained 32.1% of the variance in vitamin D status (Nagelkerke R² = 0.321). According to the analysis results, maternal non-use of vitamin D during pregnancy significantly increased the likelihood of both vitamin D insufficiency (OR = 7.46, 95% CI: 2.61–21.33, p < 0.001) and vitamin D deficiency (OR = 15.27, 95% CI: 5.82–40.02, p < 0.001) in children. In addition, irregular use of vitamin D supplementation in infants was significantly associated with both insufficiency (OR = 7.65, 95% CI: 1.96–29.81, p = 0.003) and deficiency (OR = 28.16, 95% CI: 8.21–96.64, p < 0.001). The absence of supplementation also significantly increased the risk of vitamin D deficiency (OR = 12.69, 95% CI: 4.58–35.20, p < 0.001), although its association with insufficiency was not statistically significant (p = 0.071). In contrast, child age and feeding category were not independently associated with vitamin D status in the multivariable model (p > 0.05). Discussion Vitamin D is a hormone that plays a critical role in calcium and phosphorus metabolism and bone mineralization [3]. However, the low vitamin D content of breast milk and limited exposure of children to sunlight increase the risk of vitamin D deficiency, particularly among children aged 6–24 months [10]. Therefore, assessing vitamin D status in early childhood is important for evaluating the effectiveness of prophylaxis programs and for developing strategies to prevent deficiency. In this study, vitamin D deficiency was detected in 20.6% of the children, insufficiency in 10.5%, and normal serum 25(OH)D levels in 68.9%. A large-scale study conducted in Türkiye reported that the prevalence of vitamin D deficiency was 7% among children under one year of age and 8% among those aged 1–10 years. In the same study, the mean serum 25(OH)D levels were reported as 37.2 ng/mL and 27.1 ng/mL, respectively [23]. In addition, another large-scale study evaluating healthy children aged 0–18 years reported that the proportions of children with normal vitamin D levels were 84.7% among infants and 73.3% among young children. In the same study, the prevalence of low vitamin D levels (<20 ng/mL) was reported as 15.3% in infants and 26.7% in young children [10]. In a meta-analysis conducted in Türkiye, Alpdemir and Alpdemir (2019) evaluated a total of 111,582 cases and reported that the prevalence of vitamin D deficiency in the general population was 63%, with rates of 39.8% among children and 63.5% among adults [24]. Differences between studies may be explained by various factors, including sample characteristics, geographic and seasonal variations, sunlight exposure, dietary habits, and differences in vitamin D supplementation practices. Nevertheless, the present findings indicate that although vitamin D levels may be relatively higher during early childhood, vitamin D deficiency and insufficiency remain important public health concerns in childhood. Within the national vitamin D supplementation program implemented in Türkiye, regular vitamin D supplementation is recommended for infants, which may be one of the main reasons for the high proportion of sufficient vitamin D levels observed in our study [6]. No significant differences were found in serum 25(OH)D levels according to the child’s sex, family income, number of siblings, family type, parental employment status, maternal age, or feeding type. These findings are consistent with studies suggesting that physiological and environmental factors may have a limited influence on 25(OH)D levels during infancy [19,25]. Although the univariate analyses in this study showed that serum 25(OH)D levels differed according to age groups, child age did not remain an independent predictor in the multivariable regression model. This finding suggests that the observed effect of age may be explained more by differences in supplementation behaviors rather than chronological age. In our study, children aged 12–18 months had higher serum 25(OH)D levels than those older than 18 months, and children who received regular vitamin D supplementation had higher 25(OH)D levels compared with those who used supplementation irregularly or not at all. These findings are consistent with previous studies showing that initiating vitamin D supplementation during the first year of life and maintaining regular use increases serum vitamin D levels [10,19]. Similarly, Hurmuzlu Kozler and Saylı (2022) reported that 83% of children received vitamin D supplementation during the first year of life, whereas this proportion decreased to only 28% between 13 and 24 months of age [5]. The vitamin D content of breast milk largely depends on the mother’s vitamin D status. Therefore, insufficient maternal vitamin D levels during pregnancy and lactation may adversely affect the infant’s vitamin D status [26]. Indeed, maternal vitamin D supplementation during pregnancy has been reported to increase maternal serum 25(OH)D levels, thereby strengthening the primary vitamin D pool transferred to the fetus via the placenta and positively influencing neonatal and cord blood 25(OH)D levels [27]. Previous studies have also demonstrated that maternal vitamin D status plays a key role in determining neonatal vitamin D levels and that mothers who receive prenatal vitamin D supplementation have higher serum 25(OH)D levels, as do their newborns [28]. Similarly, maternal vitamin D supplementation has been shown to significantly increase both maternal and infant serum 25(OH)D concentrations, highlighting the importance of adequate vitamin D intake during pregnancy [29]. In this study, maternal non-use of vitamin D during pregnancy and irregular vitamin D supplementation in infants were associated with lower serum 25(OH)D levels. Vitamin D deficiency during pregnancy is known to be highly prevalent. For example, a study conducted in Tehran reported vitamin D deficiency in 27% of pregnant women and vitamin D insufficiency in 73%, while none of the participants had sufficient vitamin D levels [30]. Studies conducted in Türkiye have also shown that vitamin D deficiency among pregnant women is highly prevalent, with reported rates ranging from 35% to 95% [24]. Since maternal vitamin D status has been reported to be closely associated with neonatal and infant vitamin D levels, vitamin D supplementation during pregnancy is considered an important factor in determining vitamin D status during early childhood. According to the multivariable multinomial logistic regression analysis, children whose mothers did not use vitamin D during pregnancy had approximately a 15-fold higher likelihood of vitamin D deficiency (OR = 15.27, 95% CI: 5.82–40.02). In addition, irregular use of vitamin D supplementation in infants increased the risk of vitamin D deficiency by approximately 28-fold (OR = 28.16, 95% CI: 8.21–96.64). These findings suggest that vitamin D status in early life is influenced not only by the child’s feeding characteristics but also by maternal health behaviors and the regular use of vitamin D supplementation. The literature also indicates that maternal health behaviors influence children’s vitamin D supplementation practices and adherence to regular use [31]. In addition, studies examining the long-term effects of maternal vitamin D status on child health have reported similar findings. Low maternal serum 25(OH)D levels during pregnancy may increase the risk of rickets, respiratory diseases, and other health problems in early childhood. In a study conducted by Nasantogtokh et al. (2023), children of mothers who used higher doses of vitamin D during pregnancy were reported to have a lower incidence of respiratory diseases [32]. One of the important findings of this study is that regular use of vitamin D supplementation in infants is a key determinant of serum vitamin D levels. Children who received regular supplementation had significantly higher serum 25(OH)D levels, whereas irregular use or absence of supplementation substantially increased the risk of vitamin D deficiency. These findings are consistent with previous studies reported in the literature and indicate that regular vitamin D supplementation is effective in increasing serum vitamin D levels [10,19]. In addition, the daily dose of vitamin D was found to influence serum levels. Children who received more than three drops of vitamin D per day had higher serum 25(OH)D levels. However, the literature indicates that vitamin D intake above the recommended dose does not provide additional benefits and unnecessary high-dose supplementation is not recommended [33]. In a study conducted by Şolt Kırca and Dolgun (2018), 60% of mothers reported giving their infants three drops of vitamin D per day, whereas 40% reported giving more than three drops [34]. This finding suggests that although parents recognize the importance of vitamin D supplementation, there may still be gaps in knowledge regarding the recommended dosage. Guidance from healthcare professionals can encourage families to administer supplements regularly and at the correct dosage, thereby helping to maintain optimal 25(OH)D levels in children [19, 31]. Therefore, families should be informed not only about the importance of vitamin D supplementation but also about the correct dosage and the importance of regular use. Infant feeding practices have been reported to influence vitamin D status. In a study conducted in northern Taiwan, the prevalence of vitamin D deficiency was found to be 86.1% among infants exclusively breastfed, 51.9% among those receiving mixed feeding, and 38.5% among those fed with formula [35] In the present study, although some differences were observed in univariate analyses when examining the relationship between feeding type and serum vitamin D levels, feeding type did not remain an independent predictor in the multivariable analysis. This finding suggests that vitamin D supplementation practices may be more influential than feeding type in determining vitamin D status. In Türkiye, the free distribution of vitamin D drops for infants through the national supplementation program [6] may have increased access to supplementation and reduced the potential influence of feeding type on vitamin D levels. Overall, the findings indicate that three main factors play a key role in achieving optimal serum 25(OH)D levels during early childhood: maternal vitamin D use during pregnancy, regular vitamin D supplementation in infants, and appropriate dosing. In particular, the decrease in vitamin D supplementation during the transition to complementary feeding may increase the risk of vitamin D deficiency in children. Therefore, it is important for healthcare professionals to emphasize that vitamin D supplementation should be continued regularly not only during the first year of life but also for the recommended duration thereafter. Strengths and Limitations This study has several strengths and limitations. One of the main strengths of the study is the use of multivariable statistical analyses to evaluate factors associated with serum 25(OH)D levels in early childhood. By controlling for potential confounding variables, independent predictors of vitamin D status were identified more reliably. In addition, the simultaneous evaluation of maternal vitamin D use during pregnancy, infant vitamin D supplementation practices, and feeding characteristics provides a comprehensive perspective on determinants of vitamin D status during the complementary feeding period. These findings contribute to the existing literature by highlighting the importance of early-life factors influencing vitamin D status in young children. However, several limitations should be considered when interpreting the findings. First, the cross-sectional design of the study does not allow causal relationships to be established between vitamin D supplementation practices and serum 25(OH)D levels. Second, some of the data were obtained based on parental self-report, which may be subject to recall bias or reporting bias. Third, the study was conducted in a single tertiary care hospital, which may limit the generalizability of the results to other regions or primary healthcare settings. Additionally, important determinants of vitamin D status, such as sunlight exposure, detailed dietary intake, seasonal variation, and potential genetic factors, were not comprehensively assessed. Finally, serum 25(OH)D levels were measured at a single time point, which may not fully reflect potential longitudinal fluctuations in vitamin D status. Future multicenter studies with larger and more diverse populations are needed to better understand the determinants of vitamin D status during early childhood and to inform more effective prevention strategies. Conclusion This study evaluated vitamin D supplementation practices and serum 25(OH)D levels among children aged 6–24 months in Turkey. The findings indicate that maternal vitamin D use during pregnancy, regular infant supplementation, and appropriate dosing are key independent determinants of optimal serum 25(OH)D levels in early childhood. Although most families reported regular supplementation, irregular use and variations in dosage were still observed, particularly as children grew older. In addition, instances of intake above the recommended dose suggest that some families may still have uncertainties regarding appropriate dosing. These findings emphasize the importance of initiating education on vitamin D supplementation during pregnancy and maintaining continuous parental guidance throughout infancy and early childhood. Strengthening follow-up and reminder systems within family medicine and pediatric healthcare services may improve adherence to regular and appropriate supplementation. Considering the increasing financial burden of vitamin D testing in Turkey and the testing restrictions implemented by the Ministry of Health in 2020 [36], identifying high-risk groups and prioritizing targeted screening or prophylaxis strategies may represent a more rational approach than broad population-based testing. Aligning vitamin D testing indications with evidence-based risk stratification may contribute to more efficient use of healthcare resources both in Turkey and globally. Declarations Conflict of Interest The authors have no conflicts of interest to declare. Financial Disclosure The authors declared that this study received no financial support. Author Contribution M.T. conceived and designed the study, collected the data, performed the statistical analyses, and drafted the manuscript. A.Ç. contributed to the study design, literature review, and critically revised the manuscript for important intellectual content. Both authors approved the final version of the manuscript and agree to be accountable for all aspects of the work. Acknowledgement We would like to extend our gratitude to participants. References Hossein-nezhad A, Holick MF (2013) Vitamin D for health: a global perspective. 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Behav Res Methods 41(4):1149–1160. https://doi.org/10.3758/BRM.41.4.1149 Holick MF (2009) Vitamin D status: measurement, interpretation, and clinical application. Ann Epidemiol 19(2):73–78. https://doi.org/10.1016/j.annepidem.2007.12.001 Yeşiltepe-Mutlu G, Aksu ED, Bereket A, Hatun Ş (2020) Vitamin D status across age groups in Turkey: results of 108,742 samples from a single laboratory. J Clin Res Pediatr Endocrinol 12(3):248–256. https://doi.org/10.4274/jcrpe.galenos.2019.2019.0097 Alpdemir M, Alpdemir MF (2019) Vitamin D deficiency status in Turkey: a meta-analysis. Int J Med Biochem 2(3):118–131. https://doi.org/10.14744/ijmb.2019.04127 Türe E, Müderrisoğlu S, Acı R, Çubukçu M, Erdem MA (2020) Adölesan ve çocuklarda D vitamini düzeylerinin yaş, cinsiyet ve mevsimsel özelliklere göre değerlendirilmesi. Ankara Med J 20(2):380–386. https://doi.org/10.5505/amj.2020.70893 Maghbooli Z, Hossein-Nezhad A, Shafaei AR, Karimi F, Madani FS, Larijani B (2007) Vitamin D status in mothers and their newborns in Iran. BMC Pregnancy Childbirth 7:1. https://doi.org/10.1186/1471-2393-7-1 Karras SN, Wagner CL, Castracane VD (2018) Understanding vitamin D metabolism in pregnancy: from physiology to pathophysiology and clinical outcomes. Metabolism: clinical and experimental. 86:112–123. https://doi.org/10.1016/j.metabol.2017.10.001 Kokkinari A, Dagla M, Antoniou E, Lykeridou A, Kyrkou G, Bagianos K et al (2024) The correlation between maternal and neonatal vitamin D (25(OH)D) levels in Greece: a cross-sectional study. Clin Pract 14(3):749–764. https://doi.org/10.3390/clinpract14030060 Roth DE, Morris SK, Zlotkin S et al (2018) Vitamin D supplementation in pregnancy and lactation and infant growth. N Engl J Med 379(6):535–546. https://doi.org/10.1056/NEJMoa1800927 Naseh A, Ashrafzadeh S, Rassi S (2018) Prevalence of vitamin D deficiency in pregnant mothers in Tehran and its association with serum glucose and insulin. J Matern Fetal Neonatal Med 31(17):2312–2318. https://doi.org/10.1080/14767058.2017.1342796 Açıkgöz A, Şahan AG (2021) Annelerin çocuklarına D vitamini vermeleriyle ilişkili etmenlerin belirlenmesi. STED 30(3):181–189. https://doi.org/10.17942/sted.915361 Nasantogtokh E, Ganmaa D, Altantuya S, Amgalan B, Enkhmaa D (2023) Maternal vitamin D intakes during pregnancy and child health outcome. J Steroid Biochem Mol Biol 235:106411. https://doi.org/10.1016/j.jsbmb.2023.106411 Gallo S, Comeau K, Vanstone C et al (2013) Effect of different dosages of oral vitamin D supplementation on vitamin D status in healthy breastfed infants: a randomized trial. JAMA 309(17):1785–1792. https://doi.org/10.1001/jama.2013.3404 Şolt Kırca A, Dolgun G (2018) Gebelerin kendileri ve bebekleri için D vitamini kullanım farkındalığı. Anadolu Hemşirelik Sağlık Bilim Derg 21:18–24 Chen CM, Mu SC, Chen YL et al (2020) Infants’ vitamin D nutritional status in the first year of life in northern Taiwan. Nutrients 12(2):404. https://doi.org/10.3390/nu12020404 Yılmaz G, Aydoğan N, Sezer S et al (2021) Assessment of regulation on vitamin D test requesting in terms of rational laboratory use. Turk J Biochem 46(2):173–181. https://doi.org/10.1515/tjb-2020-0175 Tables Table 1 Participant Characteristics According to Serum 25(OH)D Levels Variables (n=267) n (%) Vitamin D3 level (Mean ± SD) Age group 18 months (3) 44 (16.5%) 57.00 ± 41.80 Test, p F=4.68, p= 0.011 Post Hoc [1-3] Child’s sex Girl 141 (52.8%) 70.76 ± 35.63 Boy 126 (47.2%) 67.32 ± 35.36 Test, p t=0.790, p= 0.430 Gestational age at birth <38 weeks 88 (33.0%) 75.44 ± 33.33 ≥38 weeks 179 (67.0%) 66.05 ± 36.18 Test, p t=-2.05, p= 0.042 Number of siblings Only child 131 (49.1%) 72.63 ± 34.45 1 sibling 118 (44.2%) 67.83 ± 37.03 ≥2 siblings 18 (6.7%) 52.33 ± 27.90 Test, p F=3.936, p=0.026 Parental employment Both parents not working 7 (2.6%) 52.57 ± 32.30 Both parents working 118 (44.2%) 74.18 ± 33.65 Only one parent working 142 (53.2%) 65.77 ± 36.66 Test, p F=2.623, p=0.074 Mother’s age 35 years 28 (10.5%) 69.10 ± 34.67 Test, p F=0.357, p=0.713 Family income Income expenses 108 (40.4%) 71.40 ± 38.65 Test, p F=1.20, p=0.310 Note: Bold values indicate statistical significance at the p < .05. Abbreviations: SD, standard deviation; t: Independent samples t-test; F: one-way ANOVA Table 2 Feeding and Supplementation Characteristics Associated with Serum 25(OH)D Levels Variables (n=267) n (%) Serum 25(OH)D level (Mean ± SD) Feeding category Milk-based feeding 29 (10.9%) 75.79 ± 32.45 Mixed feeding 129 (48.3%) 72.80 ± 34.19 Family diet 109 (40.8%) 63.00 ± 36.23 Test, p F=2.84, p=0.064 Maternal vitamin D use during pregnancy Yes 216 (80.9%) 75.51 ± 33.90 No 51 (19.1%) 42.15 ± 28.91 Test, p t=6.49, p<0.001 Vitamin D preparation Multivitamin (1) 25 (9.4%) 59.28 ± 26.72 Vitamin D3 drops (2) 184 (68.9%) 76.96 ± 35.48 Not used (3) 58 (21.7%) 48.56 ± 29.36 Test, p F=18.9, p 1; 2 > 3 Infant vitamin D supplementation Yes, regular (1) 179 (67.0%) 81.35 ± 32.86 Yes, irregular (2) 30 (11.2%) 36.07 ± 18.09 No (3) 58 (21.7%) 48.56 ± 29.36 Test, p F=65.8, p 2; 1 > 3 Vitamin D3 dose* 3 drops/day 120 (44.9%) 69.28 ± 33.19 >3 drops/day 64 (24.0%) 91.67 ± 35.26 Test, p t=-4.266, p <0.001 * *Analysis restricted to children receiving vitamin D3 drops. Note: Bold values indicate statistical significance at the p < .05.Abbreviations: SD, Standard Deviation. t: Independent samples t-test; F: one-way ANOVA Table 3 Multiple Linear Regression Analysis of Factors Associated with Serum 25(OH)D Levels Predictor B SE β t p Constant 85.027 5.541 — 15.346 <0.001 Child age (months) -0.483 0.451 -0.065 -1.072 0.285 Maternal vitamin D use (No vs Yes) -22.521 4.721 -0.635 -4.771 <0.001 Infant supplementation (None vs Regular) -16.657 6.711 -0.470 -2.482 0.014 Infant supplementation (Irregular vs Regular) -30.522 6.287 -0.860 -4.854 3 vs 3 drops/day) 15.619 4.890 0.440 3.194 0.002 Model fit statistics R = 0.588 R² = 0.346 Adjusted R² = 0.331 F(6,260)= 22.9, p < 0.001 Note: Bold values indicate statistical significance at the p < .05. Reference categories: maternal vitamin D use during pregnancy (Yes), regular infant supplementation, and 3 drops/day. Dependent variable: Serum 25(OH)D level. Predictors: Child age (months), gestational age, maternal vitamin D use during pregnancy, infant vitamin D supplementation status, daily vitamin D dose, and supplementation initiator. Table 4 Multinomial Logistic Regression Analysis of Factors Associated with Serum Vitamin D Status Predictor Insufficiency vs Normal OR (95% CI) p Deficiency vs Normal OR (95% CI) p Child age (months) 1.13 (0.98–1.31) 0.103 1.11 (0.97–1.27) 0.126 Maternal vitamin D use (No vs Yes) 7.46 (2.61–21.33) <0.001 15.27 (5.82–40.02) <0.001 Infant supplementation (None vs Regular) 2.87 (0.91–9.01) 0.071 12.69 (4.58–35.20) <0.001 Infant supplementation (Irregular vs Regular) 7.65 (1.96–29.81) 0.003 28.16 (8.21–96.64) <0.001 Feeding category (Milk-based vs Mixed) 2.97 (0.72–12.27) 0.132 1.97 (0.43–8.90) 0.380 Feeding category (Family diet vs Mixed) 0.45 (0.12–1.73) 0.247 0.39 (0.12–1.27) 0.117 Model fit: Likelihood ratio χ²(16) = 116, p < 0.001; Nagelkerke R² = 0.321 Note: Reference categories were normal vitamin D status, maternal vitamin D use during pregnancy (Yes), regular infant vitamin D supplementation, and mixed feeding. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9097943","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":614503560,"identity":"4ad73dcf-dd17-4cb8-b425-5bb76d3cad44","order_by":0,"name":"Mert Temuçin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8UlEQVRIiWNgGAWjYNACAzDJ/uNDBZBiZm7Aq5gHoYWZQXLGGRDNSIwWBogWad42EIOAFnv27jSJHwV3ovmlzx8w4J1XG83fDtTyo2Ibblt4zm6T7DF4ljuzL5khQXLb8dwZhxkbGHvO3MatRSJ3mzSDweHcDWeYGQ4YbjuW2wDUwszYhkeL/FuIlv1ngN5OnHMsdz5BLRK8UFt4mJkZDjbU5G4gqOVM7mbLHqCWGWeYzRgbjh3I3QjUchCfX9jbz2688ePP4dz+HsZnzH9q6nLnnT988MGPCtxa0MFhMHmAaPVAUEeK4lEwCkbBKBghAADp/1pSegygrgAAAABJRU5ErkJggg==","orcid":"","institution":"Ordu University Training and Research Hospital","correspondingAuthor":true,"prefix":"","firstName":"Mert","middleName":"","lastName":"Temuçin","suffix":""},{"id":614503564,"identity":"f41fb5b3-5304-44cd-a6f2-0d36beb26307","order_by":1,"name":"Atilla Çifci","email":"","orcid":"","institution":"Üsküdar University","correspondingAuthor":false,"prefix":"","firstName":"Atilla","middleName":"","lastName":"Çifci","suffix":""}],"badges":[],"createdAt":"2026-03-11 20:38:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9097943/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9097943/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107467520,"identity":"2750b6b9-0376-45ed-a7b6-f53b5f2f54e2","added_by":"auto","created_at":"2026-04-21 18:54:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":572957,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9097943/v1/eb090491-89be-4a53-b76d-5e366b44f57f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Maternal Vitamin D Use During Pregnancy and Infant Supplementation as Determinants of Serum 25(OH)D Levels in Children Aged 6–24 Months","fulltext":[{"header":"What is Known","content":"\u003cp\u003e\u0026bull; Vitamin D deficiency remains common in infants despite national supplementation programs.\u003c/p\u003e\n\u003cp\u003e\u0026bull; Maternal vitamin D status influences neonatal vitamin D levels.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat is New\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026bull; Maternal vitamin D use during pregnancy is a major determinant of infant serum 25(OH)D levels.\u003c/p\u003e\n\u003cp\u003e\u0026bull; Irregular infant supplementation is associated with a markedly increased risk of vitamin D deficiency.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eOver the past decade, vitamin D deficiency has received increasing attention due to its effects not only on bone health but also on various chronic diseases, including diabetes, cancer, autoimmune disorders, and infections [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Vitamin D plays a crucial role in calcium and phosphorus homeostasis and is essential for normal bone mineralization and skeletal development [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Deficiency resulting from impaired bone mineralization presents as rickets in infants and young children and as osteomalacia in post-adolescent and adult populations (Charoenngam). Rickets is characterized by delayed closure of fontanelles, lower limb deformities, short stature, and growth retardation, although vitamin D deficiency may also occur without obvious clinical manifestations [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn national studies conducted in Turkey before vitamin D supplementation became a health policy priority, the prevalence of rickets among children aged 0\u0026ndash;3 years ranged from 1.67% to 19% [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Globally, vitamin D deficiency is estimated to affect more than one billion people, with infants and young children representing one of the most vulnerable populations due to rapid growth and limited dietary vitamin D intake [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Due to limited dietary intake of vitamin D, insufficient sunlight exposure, and the lack of food fortification policies, deficiency and insufficiency are widely reported. Community-based studies report prevalence rates of approximately 15%, although some studies have reported rates as high as 90% [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Children aged 0\u0026ndash;24 months, especially during the complementary feeding period (6\u0026ndash;24 months), pregnant women, and elderly adults constitute high-risk groups [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. This period is critical because the introduction of complementary foods alters dietary diversity and vitamin D intake. In addition, the transition to complementary feeding may influence adherence to vitamin D supplementation [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn response to these risks, the Turkish Ministry of Health launched the \u0026ldquo;Project for the Prevention of Vitamin D Deficiency and the Protection of Bone Health\u0026rdquo; in 2005 and provided free daily supplementation of 400 IU of vitamin D to infants from birth until one year of age [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Due to the absence of vitamin D\u0026ndash;fortified foods in Turkey and the ongoing risk of rickets, continuation of vitamin D supplementation throughout the first three years of life is recommended [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Furthermore, adherence to vitamin D supplementation during the complementary feeding period may vary, emphasizing the importance of identifying factors that influence consistent intake, such as maternal vitamin D status, parental awareness, socioeconomic conditions, and guidance from healthcare providers [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Additionally, since 2011, the \u0026ldquo;Vitamin D Supplementation Program for Pregnant Women\u0026rdquo; has provided 1200 IU of vitamin D daily from the 12th week of gestation until six months postpartum [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Despite these initiatives, current studies indicate that one-third of children living in urban areas still experience vitamin D deficiency [\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. An additional concerning factor is maternal vitamin D deficiency, which directly affects the vitamin D levels of neonates, with reported deficiency rates among Turkish mothers ranging from 55% to 81% [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. These observations underscore the importance of developing comprehensive strategies that target both maternal and infant vitamin D status, particularly during the complementary feeding period, as well as the continued training of healthcare professionals in supplementation management [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite national vitamin D supplementation programs in Turkey, vitamin D deficiency remains common among young children. However, limited research has examined how maternal vitamin D use, infant supplementation behaviors, and feeding practices jointly influence serum 25(OH)D levels during the complementary feeding period. This stage represents an important transition in infant nutrition, during which dietary patterns change and adherence to supplementation may decline. Understanding the factors associated with serum vitamin D status during this critical developmental window is essential for improving prevention strategies. Therefore, this study aimed to evaluate serum 25(OH)D levels and vitamin D supplementation practices in children aged 6\u0026ndash;24 months and to identify maternal, supplementation-related, and feeding-related factors associated with vitamin D status.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eStudy Design\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis analytical cross-sectional study was conducted between October 1, 2023, and February 1, 2024, at the social pediatrics outpatient clinic of a tertiary state hospital in T\u0026uuml;rkiye. Children and their mothers who applied to the clinic and whose serum 25(OH)D levels were measured during routine examinations were included.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eParticipants\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eExclusion criteria were as follows: children younger than 6 months or older than 24 months; a diagnosis of rickets; disorders of vitamin D absorption or metabolism; chronic diseases that could lead to vitamin D deficiency (e.g., epilepsy, celiac disease, inflammatory bowel disease, chronic liver disease, or chronic renal failure); and serum 25(OH)D levels above 100 ng/mL. Serum 25(OH)D concentrations were measured using a chemiluminescence immunoassay method in the hospital laboratory.\u003c/p\u003e\n\u003cp\u003eAn a priori sample size calculation was performed for multiple linear regression analysis using an effect size of 0.15, an alpha level of 0.05, a power of 0.80, and six predictors. The minimum required sample size was calculated as 98 participants [21]. Since 267 mother\u0026ndash;child pairs were included in the study, the sample size was considered sufficient.\u003c/p\u003e\n\u003cp\u003eDuring the study period, 300 children were approached for participation. Of these, 15 mothers declined to participate and 18 children were excluded due to insufficient or clotted blood samples. Consequently, the final study sample consisted of 267 children and their mothers.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInstrument\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData were collected using a Data Collection Form developed by the researcher. The form consisted of two sections:\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003e\u003cstrong\u003eSociodemographic information\u003c/strong\u003e\u003cem\u003e:\u003c/em\u003e child\u0026rsquo;s age, gender, gestational week, family type, number of siblings, parents\u0026rsquo; employment status, mother\u0026rsquo;s age, and family income level.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eVitamin D use-related questions\u003c/strong\u003e: 25(OH)D level, child\u0026rsquo;s feeding type, maternal vitamin D intake during pregnancy, child\u0026rsquo;s vitamin D supplementation, type and dosage of the supplement, start time, the person who initiated supplementation, reasons for non-use, and current vitamin D status.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eAs part of the pilot study, the form was administered to 10 children and their mothers to ensure clarity and feasibility. Serum 25(OH)D levels were measured and categorized according to the criteria proposed by Holick (2009) as deficiency (\u0026lt;20 ng/mL), insufficiency (21\u0026ndash;29 ng/mL), and sufficient (\u0026ge;30 ng/mL). Pilot participants were not included in the main sample [22]. The Data Collection Form was completed by the researcher during face-to-face interviews with the mothers. The data collection process took approximately 10 minutes per participant. During the pilot study, the questions were found to be understandable, so no modifications were needed before the main study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical Analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStatistical analyses were performed using IBM SPSS Statistics for Windows, Version 26.0 (IBM Corp., Armonk, NY, USA). Continuous variables were expressed as mean \u0026plusmn; standard deviation (SD), and categorical variables were presented as numbers and percentages. Normality of continuous variables was assessed using the Shapiro\u0026ndash;Wilk test and visual inspection of histograms.\u003c/p\u003e\n\u003cp\u003eFor normally distributed variables, independent samples t-tests were used to compare two groups, and one-way analysis of variance (ANOVA) was used to compare three or more groups. Significant ANOVA results were further examined using Tukey\u0026rsquo;s post-hoc test.\u003c/p\u003e\n\u003cp\u003eMultiple linear regression analysis was conducted to identify independent predictors of serum 25(OH)D levels. Variables considered clinically relevant, including child age, maternal vitamin D use during pregnancy, infant vitamin D supplementation status, and vitamin D dose, were included in the model.\u0026nbsp;Multicollinearity among independent variables was assessed using variance inflation factors (VIF).\u003c/p\u003e\n\u003cp\u003eIn addition, multinomial logistic regression analysis was performed to examine factors associated with vitamin D insufficiency and deficiency with normal vitamin D status as the reference category. Model fit was evaluated using likelihood ratio chi-square statistics and Nagelkerke R\u0026sup2;. Statistical significance was set at p \u0026lt; 0.05.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthical approval for the study was obtained from the Ankara Bilkent City Hospital Clinical Research Ethics Committee (Decision No: E2-23-5197, Date: 25.10.2023) and the Ankara Bilkent City Hospital Pediatric Hospital Specialty Training Academic Committee (Decision No: 16, Date: 11.09.2023). The study was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 267 children were included in the study, and the sociodemographic and clinical characteristics of the participants are presented in Table 1. The mean age of the children was 13.5 \u0026plusmn; 4.8 months, and 52.8% were girls. The majority of the children were born at \u0026ge;38 weeks of gestation (67.0%), and approximately half were only children (49.1%). In 53.2% of the families, only one parent was employed, and the majority of the mothers were between 21 and 35 years of age (85.0%).\u003c/p\u003e\n\u003cp\u003eCharacteristics related to feeding practices and vitamin D use are presented in Table 2. Examination of feeding practices showed that 48.3% of the children received mixed feeding (breast milk and complementary foods), 40.8% consumed family foods, and 10.9% were fed predominantly milk-based diets. It was determined that 80.9% of the mothers used vitamin D during pregnancy. Among the children, 67.0% used vitamin D supplementation regularly, 11.2% used it irregularly, and 21.7% did not use it at all. Evaluation of serum 25(OH)D levels showed that 68.9% of the children had normal levels, 10.5% had insufficient levels, and 20.6% had deficient levels.\u003c/p\u003e\n\u003cp\u003eSerum 25(OH)D levels showed significant differences according to some sociodemographic characteristics (Table 1). In the analysis based on age groups, the serum 25(OH)D levels of children younger than 12 months were found to be significantly higher than those of children older than 18 months (F = 4.68, p = 0.011). Similarly, children born before 38 weeks of gestation had higher serum vitamin D levels than those born at \u0026ge;38 weeks (t = \u0026minus;2.05, p = 0.042). In addition, a significant difference in serum 25(OH)D levels was observed according to the number of siblings (F = 3.936, p = 0.026). However, no significant differences in serum vitamin D levels were found according to the child\u0026rsquo;s sex, parental employment status, mother\u0026rsquo;s age, or family income level (p \u0026gt; 0.05).\u003c/p\u003e\n\u003cp\u003eIn the analyses conducted according to feeding and supplementation characteristics (Table 2), it was found that the serum 25(OH)D levels of children whose mothers used vitamin D during pregnancy were significantly higher (t = 6.49, p \u0026lt; 0.001). In addition, a significant difference in serum 25(OH)D levels was observed according to the type of vitamin D preparation used (F = 18.9, p \u0026lt; 0.001). Post-hoc analysis showed that children who used vitamin D₃ drops had higher serum 25(OH)D levels than those who used multivitamins and those who did not receive supplementation. Similarly, children who used vitamin D supplementation regularly had significantly higher serum 25(OH)D levels than those who used it irregularly or not at all (F = 65.8, p \u0026lt; 0.001). Furthermore, children who received more than three drops of vitamin D per day had higher serum 25(OH)D levels than those who received three drops per day (t = \u0026minus;4.266, p \u0026lt; 0.001).\u003c/p\u003e\n\u003cp\u003eA multiple linear regression analysis was performed to evaluate the independent predictors associated with serum 25(OH)D levels (Table 3). The constructed multiple linear regression model was found to be statistically significant (F(6,260) = 22.9, p \u0026lt; 0.001) and explained 34.6% of the variance in serum 25(OH)D levels (R\u0026sup2; = 0.346; adjusted R\u0026sup2; = 0.331). According to the analysis results, maternal non-use of vitamin D during pregnancy was associated with significantly lower serum 25(OH)D levels in children (B = \u0026minus;22.521, p \u0026lt; 0.001). Similarly, irregular use of vitamin D supplementation (B = \u0026minus;30.522, p \u0026lt; 0.001) or no supplementation (B = \u0026minus;16.657, p = 0.014) in infants was associated with lower serum 25(OH)D levels compared with regular supplementation. In contrast, receiving more than three drops of vitamin D per day was associated with higher serum 25(OH)D levels compared with receiving three drops per day (B = 15.619, p = 0.002).\u003c/p\u003e\n\u003cp\u003eA multinomial logistic regression analysis was performed to examine the factors associated with vitamin D insufficiency and deficiency (Table 4). The constructed multinomial logistic regression model was found to be statistically significant (Likelihood ratio \u0026chi;\u0026sup2;(16) = 116, p \u0026lt; 0.001) and explained 32.1% of the variance in vitamin D status (Nagelkerke R\u0026sup2; = 0.321). According to the analysis results, maternal non-use of vitamin D during pregnancy significantly increased the likelihood of both vitamin D insufficiency (OR = 7.46, 95% CI: 2.61\u0026ndash;21.33, p \u0026lt; 0.001) and vitamin D deficiency (OR = 15.27, 95% CI: 5.82\u0026ndash;40.02, p \u0026lt; 0.001) in children. In addition, irregular use of vitamin D supplementation in infants was significantly associated with both insufficiency (OR = 7.65, 95% CI: 1.96\u0026ndash;29.81, p = 0.003) and deficiency (OR = 28.16, 95% CI: 8.21\u0026ndash;96.64, p \u0026lt; 0.001). The absence of supplementation also significantly increased the risk of vitamin D deficiency (OR = 12.69, 95% CI: 4.58\u0026ndash;35.20, p \u0026lt; 0.001), although its association with insufficiency was not statistically significant (p = 0.071). In contrast, child age and feeding category were not independently associated with vitamin D status in the multivariable model (p \u0026gt; 0.05).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eVitamin D is a hormone that plays a critical role in calcium and phosphorus metabolism and bone mineralization [3]. However, the low vitamin D content of breast milk and limited exposure of children to sunlight increase the risk of vitamin D deficiency, particularly among children aged 6\u0026ndash;24 months [10]. Therefore, assessing vitamin D status in early childhood is important for evaluating the effectiveness of prophylaxis programs and for developing strategies to prevent deficiency.\u003c/p\u003e\n\u003cp\u003eIn this study, vitamin D deficiency was detected in 20.6% of the children, insufficiency in 10.5%, and normal serum 25(OH)D levels in 68.9%. A large-scale study conducted in T\u0026uuml;rkiye reported that the prevalence of vitamin D deficiency was 7% among children under one year of age and 8% among those aged 1\u0026ndash;10 years. In the same study, the mean serum 25(OH)D levels were reported as 37.2 ng/mL and 27.1 ng/mL, respectively [23]. In addition, another large-scale study evaluating healthy children aged 0\u0026ndash;18 years reported that the proportions of children with normal vitamin D levels were 84.7% among infants and 73.3% among young children. In the same study, the prevalence of low vitamin D levels (\u0026lt;20 ng/mL) was reported as 15.3% in infants and 26.7% in young children [10].\u003c/p\u003e\n\u003cp\u003eIn a meta-analysis conducted in T\u0026uuml;rkiye, Alpdemir and Alpdemir (2019) evaluated a total of 111,582 cases and reported that the prevalence of vitamin D deficiency in the general population was 63%, with rates of 39.8% among children and 63.5% among adults [24]. Differences between studies may be explained by various factors, including sample characteristics, geographic and seasonal variations, sunlight exposure, dietary habits, and differences in vitamin D supplementation practices. Nevertheless, the present findings indicate that although vitamin D levels may be relatively higher during early childhood, vitamin D deficiency and insufficiency remain important public health concerns in childhood.\u003c/p\u003e\n\u003cp\u003eWithin the national vitamin D supplementation program implemented in T\u0026uuml;rkiye, regular vitamin D supplementation is recommended for infants, which may be one of the main reasons for the high proportion of sufficient vitamin D levels observed in our study [6]. No significant differences were found in serum 25(OH)D levels according to the child\u0026rsquo;s sex, family income, number of siblings, family type, parental employment status, maternal age, or feeding type. These findings are consistent with studies suggesting that physiological and environmental factors may have a limited influence on 25(OH)D levels during infancy [19,25].\u003c/p\u003e\n\u003cp\u003eAlthough the univariate analyses in this study showed that serum 25(OH)D levels differed according to age groups, child age did not remain an independent predictor in the multivariable regression model. This finding suggests that the observed effect of age may be explained more by differences in supplementation behaviors rather than chronological age. In our study, children aged 12\u0026ndash;18 months had higher serum 25(OH)D levels than those older than 18 months, and children who received regular vitamin D supplementation had higher 25(OH)D levels compared with those who used supplementation irregularly or not at all. These findings are consistent with previous studies showing that initiating vitamin D supplementation during the first year of life and maintaining regular use increases serum vitamin D levels [10,19]. Similarly, Hurmuzlu Kozler and Saylı (2022) reported that 83% of children received vitamin D supplementation during the first year of life, whereas this proportion decreased to only 28% between 13 and 24 months of age [5].\u003c/p\u003e\n\u003cp\u003eThe vitamin D content of breast milk largely depends on the mother\u0026rsquo;s vitamin D status. Therefore, insufficient maternal vitamin D levels during pregnancy and lactation may adversely affect the infant\u0026rsquo;s vitamin D status [26]. Indeed, maternal vitamin D supplementation during pregnancy has been reported to increase maternal serum 25(OH)D levels, thereby strengthening the primary vitamin D pool transferred to the fetus via the placenta and positively influencing neonatal and cord blood 25(OH)D levels [27]. Previous studies have also demonstrated that maternal vitamin D status plays a key role in determining neonatal vitamin D levels and that mothers who receive prenatal vitamin D supplementation have higher serum 25(OH)D levels, as do their newborns [28]. Similarly, maternal vitamin D supplementation has been shown to significantly increase both maternal and infant serum 25(OH)D concentrations, highlighting the importance of adequate vitamin D intake during pregnancy [29].\u003c/p\u003e\n\u003cp\u003eIn this study, maternal non-use of vitamin D during pregnancy and irregular vitamin D supplementation in infants were associated with lower serum 25(OH)D levels. Vitamin D deficiency during pregnancy is known to be highly prevalent. For example, a study conducted in Tehran reported vitamin D deficiency in 27% of pregnant women and vitamin D insufficiency in 73%, while none of the participants had sufficient vitamin D levels [30]. Studies conducted in T\u0026uuml;rkiye have also shown that vitamin D deficiency among pregnant women is highly prevalent, with reported rates ranging from 35% to 95% [24]. Since maternal vitamin D status has been reported to be closely associated with neonatal and infant vitamin D levels, vitamin D supplementation during pregnancy is considered an important factor in determining vitamin D status during early childhood.\u003c/p\u003e\n\u003cp\u003eAccording to the multivariable multinomial logistic regression analysis, children whose mothers did not use vitamin D during pregnancy had approximately a 15-fold higher likelihood of vitamin D deficiency (OR = 15.27, 95% CI: 5.82\u0026ndash;40.02). In addition, irregular use of vitamin D supplementation in infants increased the risk of vitamin D deficiency by approximately 28-fold (OR = 28.16, 95% CI: 8.21\u0026ndash;96.64). These findings suggest that vitamin D status in early life is influenced not only by the child\u0026rsquo;s feeding characteristics but also by maternal health behaviors and the regular use of vitamin D supplementation.\u003c/p\u003e\n\u003cp\u003eThe literature also indicates that maternal health behaviors influence children\u0026rsquo;s vitamin D supplementation practices and adherence to regular use [31]. In addition, studies examining the long-term effects of maternal vitamin D status on child health have reported similar findings. Low maternal serum 25(OH)D levels during pregnancy may increase the risk of rickets, respiratory diseases, and other health problems in early childhood. In a study conducted by Nasantogtokh et al. (2023), children of mothers who used higher doses of vitamin D during pregnancy were reported to have a lower incidence of respiratory diseases [32].\u003c/p\u003e\n\u003cp\u003eOne of the important findings of this study is that regular use of vitamin D supplementation in infants is a key determinant of serum vitamin D levels. Children who received regular supplementation had significantly higher serum 25(OH)D levels, whereas irregular use or absence of supplementation substantially increased the risk of vitamin D deficiency. These findings are consistent with previous studies reported in the literature and indicate that regular vitamin D supplementation is effective in increasing serum vitamin D levels [10,19].\u003c/p\u003e\n\u003cp\u003eIn addition, the daily dose of vitamin D was found to influence serum levels. Children who received more than three drops of vitamin D per day had higher serum 25(OH)D levels. However, the literature indicates that vitamin D intake above the recommended dose does not provide additional benefits and unnecessary high-dose supplementation is not recommended [33]. In a study conducted by Şolt Kırca and Dolgun (2018), 60% of mothers reported giving their infants three drops of vitamin D per day, whereas 40% reported giving more than three drops [34]. This finding suggests that although parents recognize the importance of vitamin D supplementation, there may still be gaps in knowledge regarding the recommended dosage. Guidance from healthcare professionals can encourage families to administer supplements regularly and at the correct dosage, thereby helping to maintain optimal 25(OH)D levels in children [19, 31]. Therefore, families should be informed not only about the importance of vitamin D supplementation but also about the correct dosage and the importance of regular use.\u003c/p\u003e\n\u003cp\u003eInfant feeding practices have been reported to influence vitamin D status. In a study conducted in northern Taiwan, the prevalence of vitamin D deficiency was found to be 86.1% among infants exclusively breastfed, 51.9% among those receiving mixed feeding, and 38.5% among those fed with formula [35] In the present study, although some differences were observed in univariate analyses when examining the relationship between feeding type and serum vitamin D levels, feeding type did not remain an independent predictor in the multivariable analysis. This finding suggests that vitamin D supplementation practices may be more influential than feeding type in determining vitamin D status. In T\u0026uuml;rkiye, the free distribution of vitamin D drops for infants through the national supplementation program [6] may have increased access to supplementation and reduced the potential influence of feeding type on vitamin D levels.\u003c/p\u003e\n\u003cp\u003eOverall, the findings indicate that three main factors play a key role in achieving optimal serum 25(OH)D levels during early childhood: maternal vitamin D use during pregnancy, regular vitamin D supplementation in infants, and appropriate dosing. In particular, the decrease in vitamin D supplementation during the transition to complementary feeding may increase the risk of vitamin D deficiency in children. Therefore, it is important for healthcare professionals to emphasize that vitamin D supplementation should be continued regularly not only during the first year of life but also for the recommended duration thereafter.\u003c/p\u003e\n\u003cp\u003eStrengths and Limitations\u003c/p\u003e\n\u003cp\u003eThis study has several strengths and limitations. One of the main strengths of the study is the use of multivariable statistical analyses to evaluate factors associated with serum 25(OH)D levels in early childhood. By controlling for potential confounding variables, independent predictors of vitamin D status were identified more reliably. In addition, the simultaneous evaluation of maternal vitamin D use during pregnancy, infant vitamin D supplementation practices, and feeding characteristics provides a comprehensive perspective on determinants of vitamin D status during the complementary feeding period. These findings contribute to the existing literature by highlighting the importance of early-life factors influencing vitamin D status in young children.\u003c/p\u003e\n\u003cp\u003eHowever, several limitations should be considered when interpreting the findings. First, the cross-sectional design of the study does not allow causal relationships to be established between vitamin D supplementation practices and serum 25(OH)D levels. Second, some of the data were obtained based on parental self-report, which may be subject to recall bias or reporting bias. Third, the study was conducted in a single tertiary care hospital, which may limit the generalizability of the results to other regions or primary healthcare settings. Additionally, important determinants of vitamin D status, such as sunlight exposure, detailed dietary intake, seasonal variation, and potential genetic factors, were not comprehensively assessed. Finally, serum 25(OH)D levels were measured at a single time point, which may not fully reflect potential longitudinal fluctuations in vitamin D status.\u003c/p\u003e\n\u003cp\u003eFuture multicenter studies with larger and more diverse populations are needed to better understand the determinants of vitamin D status during early childhood and to inform more effective prevention strategies.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study evaluated vitamin D supplementation practices and serum 25(OH)D levels among children aged 6\u0026ndash;24 months in Turkey. The findings indicate that maternal vitamin D use during pregnancy, regular infant supplementation, and appropriate dosing are key independent determinants of optimal serum 25(OH)D levels in early childhood. Although most families reported regular supplementation, irregular use and variations in dosage were still observed, particularly as children grew older. In addition, instances of intake above the recommended dose suggest that some families may still have uncertainties regarding appropriate dosing.\u003c/p\u003e\n\u003cp\u003eThese findings emphasize the importance of initiating education on vitamin D supplementation during pregnancy and maintaining continuous parental guidance throughout infancy and early childhood. Strengthening follow-up and reminder systems within family medicine and pediatric healthcare services may improve adherence to regular and appropriate supplementation.\u003c/p\u003e\n\u003cp\u003eConsidering the increasing financial burden of vitamin D testing in Turkey and the testing restrictions implemented by the Ministry of Health in 2020 [36], identifying high-risk groups and prioritizing targeted screening or prophylaxis strategies may represent a more rational approach than broad population-based testing. Aligning vitamin D testing indications with evidence-based risk stratification may contribute to more efficient use of healthcare resources both in Turkey and globally.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eConflict of Interest\u003c/h2\u003e\n\u003cp\u003eThe authors have no conflicts of interest to declare.\u003c/p\u003e\n\u003ch2\u003eFinancial Disclosure\u003c/h2\u003e\n\u003cp\u003eThe authors declared that this study received no financial support.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eM.T. conceived and designed the study, collected the data, performed the statistical analyses, and drafted the manuscript. A.\u0026Ccedil;. contributed to the study design, literature review, and critically revised the manuscript for important intellectual content. Both authors approved the final version of the manuscript and agree to be accountable for all aspects of the work.\u003c/p\u003e\n\u003ch2\u003eAcknowledgement\u003c/h2\u003e\n\u003cp\u003eWe would like to extend our gratitude to participants.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHossein-nezhad A, Holick MF (2013) Vitamin D for health: a global perspective. Mayo Clin Proc 88(7):720\u0026ndash;755. https://doi.org/10.1016/j.mayocp.2013.05.011\u003c/li\u003e\n\u003cli\u003eSaggese G, Vierucci F, Boot AM, Czech-Kowalska J et al (2015) Vitamin D in childhood and adolescence: an expert position statement. Eur J Pediatr 174(5):565\u0026ndash;576. https://doi.org/10.1007/s00431-015-2524-6\u003c/li\u003e\n\u003cli\u003ePludowski P, Holick MF, Grant WB, Konstantynowicz J et al (2018) Vitamin D supplementation guidelines. 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https://doi.org/10.3758/BRM.41.4.1149\u003c/li\u003e\n\u003cli\u003eHolick MF (2009) Vitamin D status: measurement, interpretation, and clinical application. \u003cem\u003eAnn Epidemiol\u003c/em\u003e 19(2):73\u0026ndash;78. https://doi.org/10.1016/j.annepidem.2007.12.001\u003c/li\u003e\n\u003cli\u003eYeşiltepe-Mutlu G, Aksu ED, Bereket A, Hatun Ş (2020) Vitamin D status across age groups in Turkey: results of 108,742 samples from a single laboratory. \u003cem\u003eJ Clin Res Pediatr Endocrinol\u003c/em\u003e 12(3):248\u0026ndash;256. https://doi.org/10.4274/jcrpe.galenos.2019.2019.0097\u003c/li\u003e\n\u003cli\u003eAlpdemir M, Alpdemir MF (2019) Vitamin D deficiency status in Turkey: a meta-analysis. \u003cem\u003eInt J Med Biochem\u003c/em\u003e 2(3):118\u0026ndash;131. https://doi.org/10.14744/ijmb.2019.04127\u003c/li\u003e\n\u003cli\u003eT\u0026uuml;re E, M\u0026uuml;derrisoğlu S, Acı R, \u0026Ccedil;ubuk\u0026ccedil;u M, Erdem MA (2020) Ad\u0026ouml;lesan ve \u0026ccedil;ocuklarda D vitamini d\u0026uuml;zeylerinin yaş, cinsiyet ve mevsimsel \u0026ouml;zelliklere g\u0026ouml;re değerlendirilmesi. \u003cem\u003eAnkara Med J\u003c/em\u003e 20(2):380\u0026ndash;386. https://doi.org/10.5505/amj.2020.70893\u003c/li\u003e\n\u003cli\u003eMaghbooli Z, Hossein-Nezhad A, Shafaei AR, Karimi F, Madani FS, Larijani B (2007) Vitamin D status in mothers and their newborns in Iran. \u003cem\u003eBMC Pregnancy Childbirth\u003c/em\u003e 7:1. https://doi.org/10.1186/1471-2393-7-1\u003c/li\u003e\n\u003cli\u003eKarras SN, Wagner CL, Castracane VD (2018) Understanding vitamin D metabolism in pregnancy: from physiology to pathophysiology and clinical outcomes. \u003cem\u003eMetabolism: clinical and experimental.\u003c/em\u003e86:112\u0026ndash;123. https://doi.org/10.1016/j.metabol.2017.10.001 \u003c/li\u003e\n\u003cli\u003eKokkinari A, Dagla M, Antoniou E, Lykeridou A, Kyrkou G, Bagianos K et al (2024) The correlation between maternal and neonatal vitamin D (25(OH)D) levels in Greece: a cross-sectional study. \u003cem\u003eClin Pract\u003c/em\u003e 14(3):749\u0026ndash;764. https://doi.org/10.3390/clinpract14030060\u003c/li\u003e\n\u003cli\u003eRoth DE, Morris SK, Zlotkin S et al (2018) Vitamin D supplementation in pregnancy and lactation and infant growth. \u003cem\u003eN Engl J Med\u003c/em\u003e 379(6):535\u0026ndash;546. https://doi.org/10.1056/NEJMoa1800927\u003c/li\u003e\n\u003cli\u003eNaseh A, Ashrafzadeh S, Rassi S (2018) Prevalence of vitamin D deficiency in pregnant mothers in Tehran and its association with serum glucose and insulin. \u003cem\u003eJ Matern Fetal Neonatal Med\u003c/em\u003e 31(17):2312\u0026ndash;2318. https://doi.org/10.1080/14767058.2017.1342796\u003c/li\u003e\n\u003cli\u003eA\u0026ccedil;ıkg\u0026ouml;z A, Şahan AG (2021) Annelerin \u0026ccedil;ocuklarına D vitamini vermeleriyle ilişkili etmenlerin belirlenmesi. \u003cem\u003eSTED\u003c/em\u003e 30(3):181\u0026ndash;189. https://doi.org/10.17942/sted.915361\u003c/li\u003e\n\u003cli\u003eNasantogtokh E, Ganmaa D, Altantuya S, Amgalan B, Enkhmaa D (2023) Maternal vitamin D intakes during pregnancy and child health outcome. \u003cem\u003eJ Steroid Biochem Mol Biol\u003c/em\u003e 235:106411. https://doi.org/10.1016/j.jsbmb.2023.106411\u003c/li\u003e\n\u003cli\u003eGallo S, Comeau K, Vanstone C et al (2013) Effect of different dosages of oral vitamin D supplementation on vitamin D status in healthy breastfed infants: a randomized trial. \u003cem\u003eJAMA\u003c/em\u003e 309(17):1785\u0026ndash;1792. https://doi.org/10.1001/jama.2013.3404\u003c/li\u003e\n\u003cli\u003eŞolt Kırca A, Dolgun G (2018) Gebelerin kendileri ve bebekleri i\u0026ccedil;in D vitamini kullanım farkındalığı. \u003cem\u003eAnadolu Hemşirelik Sağlık Bilim Derg\u003c/em\u003e 21:18\u0026ndash;24\u003c/li\u003e\n\u003cli\u003eChen CM, Mu SC, Chen YL et al (2020) Infants\u0026rsquo; vitamin D nutritional status in the first year of life in northern Taiwan. \u003cem\u003eNutrients\u003c/em\u003e 12(2):404. https://doi.org/10.3390/nu12020404\u003c/li\u003e\n\u003cli\u003eYılmaz G, Aydoğan N, Sezer S et al (2021) Assessment of regulation on vitamin D test requesting in terms of rational laboratory use. \u003cem\u003eTurk J Biochem\u003c/em\u003e 46(2):173\u0026ndash;181. https://doi.org/10.1515/tjb-2020-0175\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Participant Characteristics According to Serum 25(OH)D Levels\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"443\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariables (n=267)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003en (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eVitamin D3 level (Mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge group\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;12 months (1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e117 (43.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e76.03 \u0026plusmn; 34.09\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e12\u0026ndash;18 months (2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e106 (39.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e66.30 \u0026plusmn; 31.70\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026gt;18 months (3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e44 (16.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e57.00 \u0026plusmn; 41.80\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eF=4.68, p=\u003cstrong\u003e0.011\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePost Hoc\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e[1-3]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eChild\u0026rsquo;s sex\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eGirl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e141 (52.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e70.76 \u0026plusmn; 35.63\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eBoy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e126 (47.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e67.32 \u0026plusmn; 35.36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003et=0.790, p= 0.430\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eGestational age at birth\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;38 weeks\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e88 (33.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e75.44 \u0026plusmn; 33.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026ge;38 weeks\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e179 (67.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e66.05 \u0026plusmn; 36.18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003et=-2.05, p=\u003cstrong\u003e0.042\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eNumber of siblings\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eOnly child\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e131 (49.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e72.63 \u0026plusmn; 34.45\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1 sibling\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e118 (44.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e67.83 \u0026plusmn; 37.03\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026ge;2 siblings\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e18 (6.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e52.33 \u0026plusmn; 27.90\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eF=3.936, p=0.026\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eParental employment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eBoth parents not working\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e7 (2.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e52.57 \u0026plusmn; 32.30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eBoth parents working\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e118 (44.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e74.18 \u0026plusmn; 33.65\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eOnly one parent working\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e142 (53.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e65.77 \u0026plusmn; 36.66\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eF=2.623, p=0.074\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eMother\u0026rsquo;s age\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026lt;21 years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e12 (4.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e78.00 \u0026plusmn; 33.34\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e21\u0026ndash;35 years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e227 (85.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e68.72 \u0026plusmn; 35.77\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026gt;35 years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e28 (10.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e69.10 \u0026plusmn; 34.67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eF=0.357, p=0.713\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eFamily income\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eIncome \u0026lt; expenses\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e17 (6.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e57.00 \u0026plusmn; 34.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eIncome = expenses\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e142 (53.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e68.87 \u0026plusmn; 32.89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eIncome \u0026gt; expenses\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e108 (40.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e71.40 \u0026plusmn; 38.65\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eF=1.20, p=0.310\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eNote: Bold values indicate statistical significance at the \u003cem\u003ep \u0026lt; .05.\u003c/em\u003e Abbreviations: SD, standard deviation; t: Independent samples t-test; F: one-way ANOVA\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e Feeding and Supplementation Characteristics Associated with Serum 25(OH)D Levels\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"567\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariables (n=267)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003en\u003c/strong\u003e(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSerum 25(OH)D level (Mean \u0026plusmn; SD)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFeeding category\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eMilk-based feeding\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e29 (10.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e75.79 \u0026plusmn; 32.45\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eMixed feeding\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e129 (48.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e72.80 \u0026plusmn; 34.19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eFamily diet\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e109 (40.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e63.00 \u0026plusmn; 36.23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003eF=2.84, p=0.064\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMaternal vitamin D use during pregnancy\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e216 (80.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e75.51 \u0026plusmn; 33.90\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e51 (19.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e42.15 \u0026plusmn; 28.91\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003et=6.49, \u003cstrong\u003ep\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVitamin D preparation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eMultivitamin (1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e25 (9.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e59.28 \u0026plusmn; 26.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eVitamin D3 drops (2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e184 (68.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e76.96 \u0026plusmn; 35.48\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eNot used (3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e58 (21.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e48.56 \u0026plusmn; 29.36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003eF=18.9, \u003cstrong\u003ep\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003ePost Hoc\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003eTukey: 2 \u0026gt; 1; 2 \u0026gt; 3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInfant vitamin D supplementation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eYes, regular (1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e179 (67.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e81.35 \u0026plusmn; 32.86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eYes, irregular (2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e30 (11.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e36.07 \u0026plusmn; 18.09\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eNo (3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e58 (21.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e48.56 \u0026plusmn; 29.36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003eF=65.8, \u003cstrong\u003ep\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003ePost Hoc\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTukey:\u003c/strong\u003e \u003cstrong\u003e1 \u0026gt; 2; 1 \u0026gt; 3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVitamin D3 dose*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003e3 drops/day\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e120 (44.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e69.28 \u0026plusmn; 33.19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003e\u0026gt;3 drops/day\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e64 (24.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003e91.67 \u0026plusmn; 35.26\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 226px;\"\u003e\n \u003cp\u003eTest, p\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 265px;\"\u003e\n \u003cp\u003et=-4.266, p\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e*\u0026nbsp;*Analysis restricted to children receiving vitamin D3 drops. Note: Bold values indicate statistical significance at the p \u0026lt; .05.Abbreviations: SD, Standard Deviation. t: Independent samples t-test; F: one-way ANOVA\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u0026nbsp;\u003c/strong\u003eMultiple Linear Regression Analysis of Factors Associated with Serum 25(OH)D Levels\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"661\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 321px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePredictor\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eB\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026beta;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003et\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 321px;\"\u003e\n \u003cp\u003e\u003cem\u003eConstant\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e85.027\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e5.541\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e15.346\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 321px;\"\u003e\n \u003cp\u003eChild age (months)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e-0.483\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e0.451\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e-0.065\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e-1.072\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e0.285\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 321px;\"\u003e\n \u003cp\u003eMaternal vitamin D use (No vs Yes)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e-22.521\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e4.721\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e-0.635\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e-4.771\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 321px;\"\u003e\n \u003cp\u003eInfant supplementation (None vs Regular)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e-16.657\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e6.711\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e-0.470\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e-2.482\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.014\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 321px;\"\u003e\n \u003cp\u003eInfant supplementation (Irregular vs Regular)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e-30.522\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e6.287\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e-0.860\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e-4.854\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 321px;\"\u003e\n \u003cp\u003eVitamin D dose (\u0026gt;3 vs 3 drops/day)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e15.619\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e4.890\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.440\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e3.194\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.002\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 321px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eModel fit statistics\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"5\" valign=\"top\" style=\"width: 340px;\"\u003e\n \u003cp\u003eR = 0.588\u003c/p\u003e\n \u003cp\u003eR\u0026sup2; = 0.346\u003c/p\u003e\n \u003cp\u003eAdjusted R\u0026sup2; = 0.331\u003c/p\u003e\n \u003cp\u003eF(6,260)= 22.9, p \u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eNote: Bold values indicate statistical significance at the p \u0026lt; .05. Reference categories: maternal vitamin D use during pregnancy (Yes), regular infant supplementation, and 3 drops/day.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDependent variable:\u003c/strong\u003e Serum 25(OH)D level.\u003cbr\u003e\u003cstrong\u003ePredictors:\u003c/strong\u003e Child age (months), gestational age, maternal vitamin D use during pregnancy, infant vitamin D supplementation status, daily vitamin D dose, and supplementation initiator.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4\u0026nbsp;\u003c/strong\u003eMultinomial Logistic Regression Analysis of Factors Associated with Serum Vitamin D Status\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"642\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 245px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePredictor\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInsufficiency vs Normal OR (95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDeficiency vs Normal OR (95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 245px;\"\u003e\n \u003cp\u003eChild age (months)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e1.13 (0.98\u0026ndash;1.31)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.103\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e1.11 (0.97\u0026ndash;1.27)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.126\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 245px;\"\u003e\n \u003cp\u003eMaternal vitamin D use (No vs Yes)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e7.46 (2.61\u0026ndash;21.33)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e15.27 (5.82\u0026ndash;40.02)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 245px;\"\u003e\n \u003cp\u003eInfant supplementation (None vs Regular)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e2.87 (0.91\u0026ndash;9.01)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.071\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e12.69 (4.58\u0026ndash;35.20)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 245px;\"\u003e\n \u003cp\u003eInfant supplementation (Irregular vs Regular)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e7.65 (1.96\u0026ndash;29.81)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e28.16 (8.21\u0026ndash;96.64)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 245px;\"\u003e\n \u003cp\u003eFeeding category (Milk-based vs Mixed)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e2.97 (0.72\u0026ndash;12.27)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.132\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e1.97 (0.43\u0026ndash;8.90)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.380\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 245px;\"\u003e\n \u003cp\u003eFeeding category (Family diet vs Mixed)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003e0.45 (0.12\u0026ndash;1.73)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e0.247\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e0.39 (0.12\u0026ndash;1.27)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 57px;\"\u003e\n \u003cp\u003e0.117\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" valign=\"top\" style=\"width: 642px;\"\u003e\n \u003cp\u003eModel fit: Likelihood ratio \u0026chi;\u0026sup2;(16) = 116, p \u0026lt; 0.001; Nagelkerke R\u0026sup2; = 0.321\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eNote: Reference categories were normal vitamin D status, maternal vitamin D use during pregnancy (Yes), regular infant vitamin D supplementation, and mixed feeding.\u003c/p\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":"Vitamin D, infants, supplementation, complementary feeding, 25(OH)D","lastPublishedDoi":"10.21203/rs.3.rs-9097943/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9097943/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe complementary feeding period is a critical stage for infant nutrition and vitamin D status. This study aimed to determine whether maternal vitamin D use during pregnancy and infant supplementation predict serum 25(OH)D levels in children aged 6\u0026ndash;24 months. This analytical cross-sectional study included 267 mother\u0026ndash;child pairs between November 2023 and February 2024. Sociodemographic characteristics, feeding practices, vitamin D supplementation habits, and serum 25(OH)D levels were collected. Group comparisons were performed using independent samples t-tests and one-way ANOVA, and predictors of serum 25(OH)D levels were assessed using multiple linear and multinomial logistic regression analyses. The mean age of the children was 13.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8 months. Regular vitamin D supplementation was reported in 67.0% of children, whereas 11.3% used supplementation irregularly and 21.7% received none. Vitamin D deficiency was detected in 20.6% of children and insufficiency in 10.5%. Children whose mothers used vitamin D during pregnancy had significantly higher serum 25(OH)D levels (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In the regression model, maternal vitamin D use during pregnancy, infant supplementation status, and vitamin D dose were significant predictors of serum 25(OH)D levels (R\u0026sup2; = 0.346, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Maternal non-use of vitamin D during pregnancy increased the risk of vitamin D deficiency (OR\u0026thinsp;=\u0026thinsp;15.27, 95% CI 5.82\u0026ndash;40.02), and irregular supplementation was associated with markedly higher odds of deficiency (OR\u0026thinsp;=\u0026thinsp;28.16, 95% CI 8.21\u0026ndash;96.64).\u003c/p\u003e \u003cp\u003e \u003cem\u003eConclusion\u003c/em\u003e: Maternal vitamin D use during pregnancy and regular infant supplementation are key determinants of optimal serum 25(OH)D levels in early childhood.\u003c/p\u003e","manuscriptTitle":"Maternal Vitamin D Use During Pregnancy and Infant Supplementation as Determinants of Serum 25(OH)D Levels in Children Aged 6–24 Months","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-31 15:18:31","doi":"10.21203/rs.3.rs-9097943/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":"14a9b642-b76b-48a2-8c12-feed26dce4a1","owner":[],"postedDate":"March 31st, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-21T18:54:26+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-31 15:18:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9097943","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9097943","identity":"rs-9097943","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}