Association of body mass index on sexual function in women with endometriosis: A cross-sectional study

Endometriosis is a persistent gynecological disorder marked by the presence of tissue resembling the endometrium outside the uterine cavity. This ectopic tissue remains responsive to hormonal changes during the menstrual cycle, leading to chronic inflammation [ 1 , 2 ]. Due to its diverse symptomatology, endometriosis often mimics other medical conditions, complicating timely diagnosis. Common symptoms include intense menstrual pain (dysmenorrhea), pain during intercourse (dyspareunia), abdominal and pelvic discomfort that may extend to the lower back, as well as pain during urination and gynecological assessments [ 3 – 5 ]. The estimated prevalence of endometriosis ranges between 7% and 15% among women of reproductive age in the general population, with substantially higher rates reported in clinic-based populations such as women with infertility (30–50%) or chronic pelvic pain (≈50%) [ 5 , 6 ]. Moreover, it is diagnosed in nearly half of patients experiencing chronic pelvic pain syndrome [ 7 ]. However, because some individuals remain asymptomatic, the true prevalence is difficult to determine, posing challenges to precise epidemiological evaluation [ 6 , 8 ]. In assessing sexual function, the Female Sexual Functioning Index (FSFI), a comprehensive 19-item questionnaire where higher scores denote better sexual function, has been employed [ 9 ]. According to findings by Shi et al., women diagnosed with endometriosis exhibited significantly lower FSFI scores in comparison to their healthy counterparts, indicating impaired sexual well-being [ 10 ]. Endometriosis can also intrude on various facets of a woman’s life, including her sexual relationships, leading to increased strain within these relationships [ 11 ]. Evidence suggests that the symptoms of endometriosis can negatively affect intimate and sexual relationships [ 12 – 14 ]. Sexuality involves both physical and emotional aspects and has a major correlation on a woman’s overall well-being, including her psychological health and relationships. A number of epidemiological studies reported that women with endometriosis normally have a lower body mass index (BMI) [ 15 , 16 ] or are underweight [ 17 , 18 ]. However, few studies have investigated the relationship between BMI and endometriosis and especially with FSFI score among women with endometriosis. Previous studies showed that the association of BMI and sexual dysfunction in women was inconsistent [ 19 – 21 ]. Although BMI is a widely used and simple anthropometric measure, it is a crude proxy for metabolic health and does not capture differences in body composition, fat distribution, or muscle mass [ 22 ]. Nevertheless, BMI remains a pragmatic measure in large-scale epidemiological studies and can highlight trends relevant to sexual health in women with endometriosis. Despite increasing evidence highlighting the significant correlation of endometriosis on sexual health, few studies have explored modifiable factors that may contribute to sexual dysfunction in this population. BMI is one such factor that has been inconsistently correlated with both endometriosis and sexual dysfunction in the general female population. While some epidemiological studies suggest that women with endometriosis tend to have lower BMI or are more frequently underweight, others report an increased prevalence of dysmenorrhea and pelvic pain among obese women with endometriosis. However, the specific relationship between BMI and sexual function, as measured by the FSFI, has been poorly studied in women with endometriosis. Understanding this relationship is crucial, as both underweight and overweight status may influence hormonal balance, inflammatory processes, pain perception, and body image, factors known to affect sexual health. Moreover, identifying whether the association between BMI and sexual function varies according to the severity of endometriosis symptoms may help target interventions more effectively. While both underweight and overweight status have been linked to sexual dysfunction in the general female population, women with endometriosis represent a particularly vulnerable group in whom BMI may play a more critical role. This is because excess or insufficient adiposity can exacerbate disease-specific mechanisms such as chronic inflammation, dyspareunia, hormonal imbalance, and psychological distress, thereby amplifying the correlation of BMI on sexual well-being [ 23 , 24 ]. Understanding this interaction is essential to identify potentially modifiable factors contributing to impaired sexual health in this population. In addition, BMI may not only act as an exposure but can also be influenced by endometriosis itself. Chronic pain, reduced physical activity, fatigue, and psychological distress associated with the disease may lead to weight gain or weight loss, thereby complicating the interpretation of BMI as a risk factor [ 8 , 24 ]. This bidirectional relationship highlights the need to examine BMI in the specific context of endometriosis rather than extrapolating from general female populations. Several psychological, medical, and socioeconomic factors are known to affect both BMI and sexual health in women, such as depression, comorbid metabolic conditions, and medication use. While these influences are well established, little is known about how BMI interacts with the specific symptom burden of endometriosis to shape sexual function. Addressing this knowledge gap may help identify BMI as a potentially modifiable factor within the complex interplay of biological and psychosocial determinants of sexual well-being. Therefore, this study aimed to investigate the association between body mass index and sexual function, as measured by the FSFI, among women with endometriosis, while also accounting for the number of symptoms experienced.

1,586 women with endometriosis responded to the online questionnaire, among them, 759 (48%) had children, 1,247 (79%) were in a relationship, 410 (26%) declared smoking tobacco ( Table 1 ). Characteristics of the population according to the BMI levels are shown in Table 2 . Their overall mean for FSFI was 17 (SD: 9) and for BMI 26 (SD: 6) kg/m 2 ( Table 1 ). When considering dichotomization of our study population according to FSFI cutoff (i.e., FSFI<26.55), we observed significant difference for age (p = 0.043), being in a relationship (p < 0.001) and the number of endometriosis symptoms (p = 0.007). As shown in Fig 1 , we observed a statistically significant negative linear relationship between BMI and FSFI scores (FSFI = 18.83–0.082 × BMI; p = 0.041), indicating that BMI > 30 kg/m 2 is correlated with lower sexual function in women with endometriosis ( Fig 1 ). In practical terms, the negative adjusted beta coefficient observed for BMI (Beta = −0.07; 95% CI: −0.15 to −0.01; p = 0.044) indicates that, on average, each one-unit increase in BMI (kg/m²) is correlated with a 0.07-point decrease in the FSFI score, reflecting a subtle but statistically significant deterioration in sexual function ( Table 3 ). Although this correlation may appear modest on an individual scale, its clinical relevance becomes more apparent when considering higher BMI ranges or in women already experiencing substantial symptom burden. We observed a significant interaction between BMI and the number of endometriosis symptoms (p for interaction, p = 0.020). Fig 2 illustrates the interaction between BMI and the number of endometriosis symptoms in relation to sexual function. Panel A displays the estimated correlation of BMI (as a continuous variable) on FSFI across subgroups of women categorized by symptom count. Notably, a significant negative association between BMI and FSFI was observed among women reporting seven symptoms (p = 0.003), while no significant association was detected in women with fewer symptoms. Panel B presents similar analyses using BMI categorized as high versus low, confirming that BMI BMI > 30 kg/m 2 is significantly correlated with poorer sexual function only in women with high symptom burden (p = 0.002). When considering BMI level, after adjustment for confounding factors, BMI > 30 kg/m 2 was significantly and negatively correlated with FSFI (Beta = −0.71 95% CI: −4.44; −3.39, p = 0.044) ( Table 4 ). We observed a significant interaction between BMI level and the number of endometriosis symptoms (p for interaction, p = 0.010). The significant interaction between BMI and the number of endometriosis symptoms (p for interaction = 0.010) suggests that the correlation of BMI on sexual function is not uniform across all women. Specifically, in women reporting seven endometriosis symptoms, a group likely representing those with more severe disease, the detrimental correlation of BMI BMI > 30 kg/m 2 on sexual function was amplified. In this subgroup, women with a BMI > 30 kg/m² had significantly lower FSFI scores compared to women with BMI < 25 kg/m 2 , even after adjusting for potential confounders. This finding highlights that BMI and symptom burden may act synergistically, compounding the risk of sexual dysfunction. High BMI level was only correlated to FSFI among women with 7 endometriosis symptoms ( Fig 2 ). From a clinical perspective, these results emphasize the importance of considering BMI as a modifiable factor, particularly in women with a high endometriosis symptom burden. Addressing both metabolic health and symptom management in a multidisciplinary approach may help mitigate the association of BMI extremes on sexual well-being.

In this cross-sectional study of women with self-reported endometriosis, we observed a statistically significant but small association between BMI and sexual function scores. The correlation size was of limited clinical importance, corresponding to minimal differences in FSFI per BMI unit. Thus, while BMI may contribute to sexual dysfunction in the context of high symptom burden, it is unlikely to represent a major determinant of sexual health outcomes. Importantly, our findings reflect correlations only and cannot establish causal relationships or the potential benefits of weight management interventions on sexual health. The study design also imposes notable limitations. Participants were recruited through social media, and endometriosis was self-reported without clinical confirmation or staging, which restricts external validity. BMI was self-reported rather than measured, and relevant confounders, including mental health, treatment history, hormonal therapy, and comorbid conditions, were not captured. Taken together, these factors limit the generalizability of the findings and caution against extrapolating them to all women with endometriosis. Future research should prioritize prospective longitudinal cohorts with clinically confirmed endometriosis diagnoses and staging, more representative recruitment strategies, objective measures of BMI, and comprehensive adjustment for biological, psychological, and treatment-related confounders. Such studies are needed to clarify the directionality and mechanisms underlying the observed correlations and to determine whether BMI plays a meaningful role in sexual health outcomes among women with endometriosis. -Higher BMI is linked to lower FSFI scores, with sexual dysfunction observed in both women with few and many endometriosis symptoms, highlighting a non-linear association. -Obesity exacerbates inflammation, hormonal imbalances, and pain sensitivity, worsening sexual dysfunction, particularly in women with severe endometriosis symptoms. -Targeted interventions addressing metabolic health, pain management, and psychological support are essential to improve sexual function in women with endometriosis across different BMI categories.

We designed and conducted a cross-sectional survey using survey software developed by our hospital [ 25 ]. The survey was completed anonymously to encourage honest and unbiased responses. A formal a priori sample size calculation was not performed for this study due to its exploratory, cross-sectional design and the use of an open online survey. Recruitment was conducted via social media (Instagram) with a snowball sampling approach, where initial participants were invited to share the survey link within their networks. This strategy aimed to maximize participation among women with endometriosis but did not rely on predefined quotas or structured sampling frames. No a priori sample size calculation was performed, given the exploratory nature of this study. However, a post-hoc power analysis indicated that with 1,586 participants, the study had 79.8% power (α = 0.05) to detect a small correlation size (r = 0.07; Cohen’s d = 0.14), consistent with the observed association between BMI and FSFI. The study was approved by the Foch IRB: IRB00012437 (approval number: 23-07-05) on 18 July 2023. Written consent was obtained from all participants. The study link was disseminated via social media (Instagram) where participants were asked to forward this link to others they know. All registrants were free to accept or decline the invitation, with no monetary reward received in return. Participants were also informed that they could withdraw at any time. Following internationally accepted ethical codes, respondents were duly informed of the purpose of the survey and were reminded of their participation rights before proceeding to take the survey. A research protocol was conducted to obtain approval from an ethical committee. The distribution of the questionnaire occurred between November 2023 and January 2024 in France on social media (Instagram). We closed the survey link after the workshop ended. Data were collected through an anonymous, online questionnaire hosted on a secure institutional survey platform developed by our hospital [ 25 ]. The survey was designed to prevent multiple submissions from the same participant by restricting access based on device IP addresses. Participants were also explicitly instructed to complete the questionnaire only once and were required to confirm their consent at the beginning of the survey. Furthermore, responses were screened for internal consistency, and entries with contradictory or incomplete information were excluded from the final dataset. These measures aimed to minimize the risk of duplication and ensure data integrity, although we acknowledge that complete elimination of duplicate entries cannot be guaranteed in anonymous, internet-based surveys. The recruitment strategy via Instagram and social media may have introduced selection bias by favoring younger, digitally engaged, and potentially higher-educated women. Because the survey was anonymous and did not collect detailed geographic or sociodemographic information, the representativeness of the broader population of women with endometriosis could not be assessed. To minimize duplicate entries, access was restricted by device IP addresses; however, we acknowledge that the use of multiple devices or VPNs could potentially bypass this filter. In addition, both BMI and FSFI were self-reported and therefore subject to recall or reporting bias. These limitations could not be addressed analytically in the present study and should be considered when interpreting the results. Eligible participants were women aged 18 years or older with a self-reported diagnosis of endometriosis, regardless of disease stage, who provided informed consent and completed the online questionnaire in its entirety. The diagnosis of endometriosis was based on self-report, in line with previous large-scale, survey-based studies in this field [ 8 , 25 ]. Exclusion criteria included participants under 18 years of age. Due to the anonymous and online nature of the survey, clinical confirmation of the endometriosis diagnosis, disease stage, or lesion localization could not be obtained. Endometriosis was defined exclusively on the basis of self-report, without clinical, imaging, or surgical confirmation. Information on disease stage, lesion type (superficial vs. deep infiltrating), and comorbid conditions was not collected. These factors are known to influence sexual function and therefore represent potential unmeasured confounders in our analysis. The questionnaire was divided into the following sections: Sociodemographic questions (couple status, age, educational level, children, BMI level calculated as weight (in kg) divided by height squared (in meters) and BMI categories were defined according to the World Health Organization (WHO) standards as BMI > 30 kg/m 2 , BMI between 25 and 30 kg/m 2 , and less than 25 kg/m 2 [ 26 ]. Questions related to the disease (diagnosis, symptoms, treatment, age of diagnosis etc.) Symptoms of endometriosis were defined as: pain during sexual intercourse; abnormal or heavy menstruation; infertility; pain during urination during periods; pain during bowel movements during periods, other digestive issues (diarrhea, constipation, nausea); worsening pain over time; pain, particularly excessive menstrual cramps that are felt, and other symptoms, medical treatment for endometriosis, and surgery for endometriosis. We used the validated French version of the Female Sexual Function Index (FSFI), which has been cross-culturally adapted and psychometrically validated for use in French-speaking populations [ 27 ]. The FSFI contains 19 items and collects data on 6 domains of sexual function: desire, arousal, vaginal lubrication, orgasm, satisfaction, and pain. For each domain except the pain domain, the item scores range from 0 to 5. Higher item scores indicate better function. Items in the pain domain are coded by a descending scale. To obtain the total FSFI score, the item scores within each domain are added and then multiplied by a correction factor. The resulting scores within each of the 6 domains are added to obtain a total FSFI score. Higher scores reflect better sexual function [ 9 ]. A FSFI total score under of 26.55 was considered as to be the optimal cut score for differentiating women with sexual dysfunction to women without sexual dysfunction [ 28 ]. For each of the six domains of the FSFI (desire, arousal, lubrication, orgasm, satisfaction, and pain), the sum of the item scores is multiplied by a domain-specific correction factor to standardize the domain scores and ensure that each contributes equally to the total score. The correction factors are as follows: 0.6 for desire, 0.3 for arousal, 0.3 for lubrication, 0.4 for orgasm, 0.4 for satisfaction, and 0.4 for pain [ 9 ]. The sum of these weighted domain scores yields the total FSFI score, ranging from 2 to 36, with higher scores indicating better sexual function. Characteristics of the study population were described as the mean standard deviation (SD) for continuous variables. Categorical variables were described as numbers and proportions. Comparisons between groups were performed using the Mann–Whitney test or t Student test for continuous variables. Pearson’s χ 2 test was performed for categorical variables. Multiple linear regression models were applied, with adjustment for age, number of endometriosis symptoms and couple, to investigate the relationship between FSFI and BMI. Adjustment for age, relationship status, and number of endometriosis symptoms was performed to account for known confounding factors that can influence sexual function. Age is a well-established determinant of sexual function, with studies consistently showing a decline in desire, arousal, and overall sexual satisfaction with increasing age [ 29 ]. Relationship status is also a critical factor, as being in a stable relationship is associated with higher sexual activity levels and better sexual function scores, while single status may correlate with reduced sexual activity and lower FSFI scores [ 30 ]. The number of endometriosis symptoms reflects disease severity and symptom burden, which are strongly linked to sexual dysfunction, particularly due to pain-related mechanisms such as dyspareunia and chronic pelvic pain [ 31 ]. Other potential confounders such as disease stage, parity, hormone therapy, psychiatric history, socioeconomic status, smoking, and comorbid metabolic diseases were not available in our dataset. As a result, residual confounding cannot be excluded. To explore whether the association between BMI and sexual function varied according to symptom burden, interaction term between BMI (both as a continuous and categorical variable) and the number of endometriosis symptoms was included in the multiple linear regression models. The significance of interaction terms was assessed using likelihood ratio tests comparing models with and without the interaction term. Model assumptions were systematically verified. Interaction was examined by including simultaneous BMI and the number of endometriosis sympotms. Relationships between BMI and FSFI were investigated in each subgroup of number of endometriosis symptoms. The normality of residuals was assessed statistically using the Shapiro–Wilk test. Multicollinearity between independent variables was evaluated by calculating the variance inflation factor (VIF), with all VIF values below 2 (1.05 for BMI, 1.22 for age, 1.01 for beeing in a relationship and 1.80 for symptoms of endometriosis), indicating no significant collinearity concerns. Statistics were performed using SAS software (version 9.4; SAS Institute, Carry, NC). A p value < 0.05 was considered statistically significant.