Association of dietary folate intake with endometriosis in US participants :a retrospective cross-sectional study

Association of dietary folate intake with endometriosis in US participants :a retrospective cross-sectional study | 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 Association of dietary folate intake with endometriosis in US participants :a retrospective cross-sectional study Qian Xue, Hongju Chen This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7188235/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Objective To investigate the dose-response relationship between dietary folate intake and endometriosis risk among U.S. women of reproductive age. Methods This cross-sectional study analyzed 4,024 women (aged 20–54 years) from the 1999–2006 NHANES cycles. Dietary folate intake was quantified via 24-hour recall and categorized into quartiles (Q1-Q4: 0–206, 207–300, 301–429, and 430–2,827 µg/day). Multivariable logistic regression models adjusted for sociodemographics, lifestyle factors, and dietary confounders evaluated the folate-endometriosis association. Restricted cubic splines assessed nonlinear trends. Results Among participants, 8.0% (321/4,024) reported endometriosis. Higher folate intake exhibited a dose-dependent inverse association with endometriosis risk. Compared to Q1 (reference), adjusted odds ratios (95% CI) for Q2–Q4 were 0.82 (0.59–1.14), 0.75 (0.52–1.08), and 0.63 (0.42–0.96), respectively (P for trend = 0.032). A linear threshold effect was observed, with intake ≥ 400 µg/day associated with 37% reduced risk (OR = 0.63, 95% CI:0.46–0.86; P = 0.003). Subgroup analyses revealed no significant interactions by age, BMI, or lifestyle factors (P interaction > 0.05). Conclusion Dietary folate intake demonstrates a significant inverse linear relationship with endometriosis risk in U.S. women, suggesting adequate folate consumption (≥ 400 µg/day) may mitigate disease burden. dietary folate intake endometriosis NHANES Figures Figure 1 Figure 2 Figure 3 1 Introduction Endometriosis is a challenging gynecological disease to treat. Although it is a benign condition, it shares biological characteristics with malignant tumors. Endometriosis involves the presence of endometrium-like tissue outside the uterine cavity, such as in the pelvis or vagina 1 . The complications it causes can lead to infertility, dysmenorrhea, and chronic pelvic pain 2 , significantly affecting a woman's quality of life.Endometriosis primarily causes pelvic pain symptoms, which can lead to decreased fertility. Nearly half of endometriosis patients experience significantly reduced fertility, and up to two-thirds of women with dysmenorrhea suffer from the condition. Additionally, about three-quarters of endometriosis patients report chronic pelvic pain 3 . Due to its prevalence and impact on women's health, endometriosis is considered a significant public health issue. However, the cause of endometriosis is not yet fully understood, and research is ongoing to identify modifiable risk factors for its development. Folate, also known as vitamin B9, is a crucial nutrient that plays essential roles in various physiological functions, such as neurotransmitter production, DNA synthesis, and cell division 4 . Folate also has anti-inflammatory properties, reduces oxidative stress, and plays an immunomodulatory role 5 . A series of studies have shown that folate plays a significant role in women's reproductive health. Research by Liu, P, et al. indicates that folate and other micronutrients may reduce the risk of endometriosis by decreasing the inflammatory response 6 . Another study highlighted abnormalities in folate metabolism in infertile patients with endometriosis, emphasizing the importance of adequate folate levels in improving endometriosis symptoms and infertility 7 . Additionally, one study examined the relationship between folate intake and the risk of ovarian cancer in women with endometriosis 8 . The core objective of this study is to explore in depth the possible association between daily dietary intake of folate and endometriosis in women aged 20 to 54 in the United States. We aim to enhance endometriosis prevention and treatment through this research, contributing to new advancements in the field of women's health. 2 Materials and methods 2.1 Study population Data for the study were collected by NHANES, which is a cross-sectional, population-based survey conducted by the National Center for Health Statistics. The survey utilizes a nationally representative, stratified sample, which is based on interviews and physical examinations.The data for this study were derived from four two-year NHANES cycles conducted between 1999 and 2006. Reproductive health survey information was included in these cycles. A total of 15,886 female participants were recruited after screening, but women aged under 20 years or over 54 years were excluded,those with missing endometriosis-related information, missing data on dietary folate intake, pregnant women, and those with missing data on covariates were also excluded. In total, 4,024 women were included in the study, 321 with endometriosis and 3,703 without.In this study, all methods were performed in strict compliance with relevant guidelines and regulations to ensure the scientific and standardised nature of the study. Prior to participation in NHANES, participants signed a written informed consent form in order to safeguard their rights and privacy, and in addition, the data were made publicly available on the NHANES website ( http://www.cdc.gov/nchs/nhanes.htm ). 2.2 Endometriosis assessment To identify participants with endometrial disease, we looked at their responses to the question in the reproductive health section of the questionnaire, "Have you ever been told by a doctor or other health care professional that you have endometriosis?" 2.3 Dietary folate intake Dietary folate intake, referring to the daily dietary intake of total folate, was accurately calculated from the NHANES 24-hour food recall questionnaire, which detailed the types and amounts of food consumed by the subjects 9 , 10 , as well as from thedietary interview procedure manual 11 , 12 . Participants were categorized into quartiles (Q1-Q4) based on their dietary folate intake. According to the World Health Organization's recommended daily intake of 400 µg of folate, the participants were divided into two groups: the folate deficiency group, with an intake of less than 400 µg, and the folate adequate group, with an intake of greater than or equal to 400 µg. 2.4 Covariates To ensure the accuracy of the research analysis, this study included as many relevant variables as possible. The variables analyzed were age, race/ethnicity, education level, family poverty rate income (PIR), marital status, smoking status, physical activity, body mass index (BMI), and nutrients (energy, proteins, and carbohydrates). Race/ethnicity was categorized as Non-Hispanic White, Non-Hispanic Black, Mexican American, or other race. Marital status was categorized as married/with a partner or alone. Education level was categorized based on the number of years of education received: less than 9 years, 9 to 12 years, or more than 12 years. Physical activity was classified as sedentary, moderate, or vigorous. Smoking status was categorized as never smokers, current smokers, and former smokers 13 . BMI was calculated based on weight and height, and nutrient intake (energy, proteins, and carbohydrates) was calculated based on the NHANES 24-hour food recall questionnaire and dietary interview procedure manual. 2.5 Statistical analyses This study analyzed NHANES data from 1999–2006. Continuous variables conforming to normal distributions are expressed as mean (standard deviation), while skewed distributions are expressed as median (interquartile range). Categorical variables are expressed as proportions (%).Dietary folate intake was analyzed both as a continuous variable and as an interquartile categorical variable. Multivariate logistic regression was used to calculate 95% confidence intervals (CI) for the association between dietary folate intake and endometriosis. Restricted cubic spline plots were used to confirm the linear correlation between folate intake and endometriosis, with subgroup analyses conducted to determine whether other confounders interacted. Model 1 is not adjusted. Model 2 is adjusted for demographic characteristics such as age, educational status, marital status, race/ethnicity, and family PIR. Xu et al. suggested that socio-economic and lifestyle factors are associated with the incidence of endometriosis 14 . Additionally, dietary intake, education, age, and family PIR may also affect total folate intake 15 . Furthermore, marital status and race may influence dietary habits. A previous NHANES study found an association between smoking and endometriosis 16 , possibly due to cigarette smoke inducing oxidative stress. Rowlands et al. proposed that the risk of endometriosis is related to body weight 17 . As a result, Model 3 is adjusted to include BMI, smoking status, and physical activity, in addition to the variables from Model 2. Abramiuk et al. conducted a literature review suggesting that dietary components influence the development and progression of endometriosis 18 , and three nutrients affect folate intake. Therefore, Model 4 incorporates the variables from Model 3, as well as adjustments for energy, protein consumption, and carbohydrate consumption. The statistical software program used for all analyses was R 3.3.2 ( http://www.R-project.org , The R Foundation, Shanghai, China). Additionally, Free Statistics Software 1.9 (Beijing Free Clinical Medical Technology Co., LTD) was employed for data processing and analysis 19 . A descriptive analysis was conducted for all participants. Results with p < 0.05 were considered statistically significant. 3 Results The study analyzed data from four NHANES periods (1999–2006). A total of 15,886 women participated in the study. After excluding those with missing endometriosis data, the remaining 4,412 patients were aged 20 to 54 years and did not include pregnant women. Further exclusions were made for participants with missing covariates such as BMI, smoking status, physical activity, family PIR, marital status, and education, resulting in a total of 4,024 participants included in the analysis (Fig. 1). Table 1 shows the baseline characteristics of the 4,024 participants who completed the study, with a mean age of 37.4 years. Among these, 321 (8.0%) had endometriosis. Participants who were non-Hispanic white, had higher education levels, higher household PIR, did not smoke, had a lower BMI, and had greater access to energy, protein, and carbohydrates generally had higher dietary folate intakes. It was observed that patients with endometriosis had a lower intake of folate. To investigate the effect of dietary folate intake on endometriosis, we constructed four multivariate logistic regression models, using dietary folate as a continuous variable. In Model 1, total dietary folate intake was negatively associated with endometriosis (OR: 0.93, 95% CI: 0.88–0.99, P = 0.03). After adjustment for potential confounders in Model 4, total dietary folate intake remained negatively associated with endometriosis (OR: 0.92, 95% CI: 0.85-1, P = 0.041), representing an 8% reduction in the risk of endometriosis for each 100 µg increase in folate. (Table 2 ). When dietary folate was used as a categorical variable, it was divided into four quartiles: Q1 (0-206 µg), Q2 (207–300 µg), Q3 (301–429 µg), and Q4 (430–2827 µg). In Model 1, compared to Q1, the ORs for Q2, Q3, and Q4 were 0.87, 0.81, and 0.69, respectively (p for trend = 0.002). After adjustment for potential confounders in Model 4, the ORs of endometriosis for Q2, Q3, and Q4 compared with Q1 were 0.82 (95% CI: 0.59–1.14), 0.75 (95% CI: 0.52–1.08), and 0.63 (95% CI: 0.42–0.96), respectively (p for trend = 0.032).When grouped according to the internationally recommended folate intake of 400 µg per day, if the daily folate intake was greater than or equal to 400 µg, the risk of endometriosis was reduced by 35% in Model 1. This result remained stable in Models 2, 3, and 4, with the risk of endometriosis reduced by 37% (OR = 0.63, 95% CI: 0.66–0.86, P = 0.003). These results suggest that the risk of endometriosis decreases with increasing dietary folate intake. (Table 2 ). As shown in Table 2 , dietary folate intake is correlated with endometriosis. To examine this association, we plotted a restricted cubic spline. The smooth plot in Fig. 2 shows a clear linear relationship (non-linear P = 0.667) between dietary folate intake and the risk of endometriosis after adjusted for potential confounders. By excluding the top 0.3% of extreme outliers in dietary folate intake, the plot further confirms that the risk of endometriosis decreases with increasing dietary folic acid intake.(Fig. 2) Subgroup analyses were conducted to further investigate the relationship between dietary folate intake and endometriosis. Age was divided into two groups with a cutoff at 40 years, and BMI was divided into two groups with a cutoff at 30 kg/m². Stratified regression models were used to analyze the data based on age, race, marital status, educational level, family PIR, physical activity, smoking status, and BMI. The forest plot (Fig. 3) indicated no statistically significant interactions between dietary folic acid intake and these subgroups in the association with endometriosis (P values for interaction were all > 0.05). (Fig. 3) 4 Comment 4.1 Principal Findings The study was cross-sectional and involved 4,024 participants, of whom 8.0% had endometriosis (Table 1 ). The prevalence of endometriosis in the US ranges from 6.1–8.9% 20,21 , which is consistent with our findings. Additionally, there was a negative relationship between endometriosis and dietary folate intake in US women aged 20–54 years. Participants with higher folate intake had a lower risk of endometriosis (OR: 0.63; 95% CI: 0.42–0.96) (Table 2 ). The restricted cubic spline plots further supported a significant linear relationship between folate intake and endometriosis (Fig. 2). Based on these findings, it appears that increased folate intake may reduce the prevalence of endometriosis. 4.2 Results in the Context of What is Known Endometriosis is a common gynecological condition with unknown etiology, risk factors, and effective treatments. The development of endometriosis involves a complex interplay of mechanisms that are not yet fully understood. Multiple factors such as oxidative stress, cytokine regulation, and prostaglandins are involved in the pathogenesis of endometriosis 22 . Modulation of the immune system and inflammatory cytokines has been implicated in the development of endometriosis by Voltolini et al. 23 . Further research is urgently required to gain a deeper understanding of the pathogenesis of endometriosis and to facilitate the discovery of improved treatment options. 4.3 Clinical Implications and Research Implications Folate may reduce the risk of endometriosis through several mechanisms: Anti-inflammatory effects : Folate may help reduce inflammation, a key feature of endometriosis. By reducing markers of inflammation, folate could potentially alleviate some of the symptoms associated with this condition. A study evaluating the effects of a Mediterranean diet, which included folate, on endometriosis showed that an anti-inflammatory diet could help alleviate the symptoms of endometriosis 24 . Reduces oxidative stress : The development of endometriosis is associated with increased oxidative stress. Folate, through its role in homocysteine metabolism, can help reduce oxidative stress and protect cells from damage. A study has shown that increased intake of folate may help reduce cellular oxidative stress and alleviate the symptoms of endometriosis 25 . Immunomodulation : Folate has been suggested to have immunomodulatory effects, which may help reduce immune dysfunction in patients with endometriosis. Zhang, M et al. studied endometriosis-related signaling pathways and their immunomodulation, highlighting the role of folate in regulating abnormal immune responses 26 . 4.4 Strengths and Limitations The study has several strengths: first, a robust data base: Analysing data from 4,024 participants through the reliable National Health and Nutrition Examination Survey (NHANES) database, with accurate dietary assessment through a 24-hour food recall system, provided a substantial and accurate foundation for investigating the association between dietary folate intake and endometriosis.Second, rigorous and controlled analysis: Adjusted for multiple confounding variables and demonstrated consistency across different populations, ensuring a robust analysis of the association between folate intake and endometriosis risk.Third, threshold effect identification: Identifying a specific threshold (400 µg of daily folate intake) associated with a reduced risk of endometriosis, providing practical implications for dietary recommendations.Finally,Novel insights and contributions: Providing new insights into the potential role of folate in the pathogenesis of endometriosis and the potential benefits of dietary folate intake for women's reproductive health, contributing to the limited existing research in this area. There are some limitations in this study that should be noted. First, the study's sample group was limited to American women aged 20 to 54, so the results may not be directly applicable to women of other races or countries. Second, the diagnosis of endometriosis relied primarily on a single question in the questionnaire, rather than the international standard classification of endometriosis diagnoses, which may affect diagnostic accuracy. Additionally, the accuracy and reliability of the dietary assessment were impacted by potential recall bias inherent in the 24-hour recall method, which may have introduced some bias into the study results. To more fully assess the association between folate and endometriosis, future studies using a prospective cohort design are needed to further clarify the causal relationship between folate intake and endometriosis. Conclusion This study found that dietary folate intake was inversely associated with endometriosis among in US adults. Ensuring adequate intake of folate in the diet may help reduce the risk of endometriosis or alleviate its symptoms. Declarations Acknowledgments The authors would like to thank all all the staff and participants in NHAENS 1999-2006 for their contribution in the form of donations, data collection and data sharing. Funding information This research did not receive any specific grants from public, commercial or voluntary funding bodies. Conflicts of Interest The authors have no competing interests. Data availability statement Public datasets used in this study. The names of the repositories and their accession numbers can be found at http://www.cdc.gov/ nchs/nhanes.htm (accessed: 8 Feb 2025). Ethical Compliance This study used de-identified NHANES data, which received institutional review board (IRB) approval. All participants provided informed consent, and analyses adhered to NHANES analytic guidelines. References Zondervan KT, Becker CM, Koga K, Missmer SA, Taylor RN, Viganò P. Endometriosis. Nat Rev Dis Primer . 2018;4(1):9. doi:10.1038/s41572-018-0008-5 Johnson NP, Hummelshoj L, Adamson GD, et al. World Endometriosis Society consensus on the classification of endometriosis. Hum Reprod . 2017;32(2):315-324. doi:10.1093/humrep/dew293 Giampaolino P, Della Corte L, Foreste V, Barra F, Ferrero S, Bifulco G. Dioxin and endometriosis: a new possible relation based on epigenetic theory. Gynecol Endocrinol . 2020;36(4):279-284. doi:10.1080/09513590.2019.1698024 Neurock M, Janik M, Wieckowski A. A first principles comparison of the mechanism and site requirements for the electrocatalytic oxidation of methanol and formic acid over Pt. Faraday Discuss . 2009;140:363-378. doi:10.1039/B804591G Demézio Da Silva CV, Felipe VL, Shivappa N, et al. Dietary inflammatory index score and risk of developing endometriosis: a case–control study. J Endometr Pelvic Pain Disord . 2021;13(1):32-39. doi:10.1177/2284026520967599 Liu P, Maharjan R, Wang Y, et al. Association between dietary inflammatory index and risk of endometriosis: a population-based analysis. Front Nutr . 2023;10:1077915. doi:10.3389/fnut.2023.1077915 Guedes T, Santos AA, Vieira-Neto FH, Bianco B, Barbosa CP, Christofolini DM. Folate metabolism abnormalities in infertile patients with endometriosis. Biomark Med . 2022;16(7):549-557. doi:10.2217/bmm-2021-0076 Gersekowski K, Ibiebele TI, for the Australian Ovarian Cancer Study Group, et al. Folate intake and ovarian cancer risk among women with endometriosis: a case–control study from the ovarian cancer association consortium. Cancer Epidemiol Biomarkers Prev . 2023;32(8):1087-1096. doi:10.1158/1055-9965.EPI-23-0121 Prentice RL, Mossavar-Rahmani Y, Huang Y, et al. Evaluation and comparison of food records, recalls, and frequencies for energy and protein assessment by using recovery biomarkers. Am J Epidemiol . 2011;174(5):591-603. doi:10.1093/aje/kwr140 Subar AF. Using intake biomarkers to evaluate the extent of dietary misreporting in a large sample of adults: the OPEN study. Am J Epidemiol . 2003;158(1):1-13. doi:10.1093/aje/kwg092 United States Department of Agriculture (USDA), Agriculture Research Service FSRG. Food and Nutrient Database for Dietary Studies, 5.0. Accessed Mayr 8, 2024. http://www.ars.usda. gov/ba/bhnrc/fsrg National Health and Nutrition Examination Survey (NHANES). MEC In-Person Dietary Interviewers Procedures Manual. Accessed May 8, 2024. http://www.cdc.gov/nchs/data/nhanes/nhanes_03_04/dietary_mec.pdf Huang W, Ma X, Liang H, et al. Dietary magnesium intake affects the association between serum vitamin D and type 2 diabetes: a cross-sectional study. Front Nutr . 2021;8:763076. doi:10.3389/fnut.2021.763076 Xu G, Chen L, Li Q. Association of iron metabolism markers, socioeconomic and lifestyle factors with endometriosis: A cross-sectional study. J Trace Elem Med Biol . 2023;78:127175. doi:10.1016/j.jtemb.2023.127175 Gibson RS, Anderson VP. A review of interventions based on dietary diversification or modification strategies with the potential to enhance intakes of total and absorbable zinc. Food Nutr Bull . 2009;30(1_suppl1):S108-S143. doi:10.1177/15648265090301S107 Kim H, Lee H, Kazmi S, et al. Familial risk for endometriosis and its interaction with smoking, age at menarche and body mass index: a population‐based cohort study among siblings. Bjog- Int J Obstet Gynaecol . 2021;128(12):1938-1948. doi:10.1111/1471-0528.16769 Rowlands IJ, Hockey R, Abbott JA, Montgomery GW, Mishra GD. Body mass index and the diagnosis of endometriosis: findings from a national data linkage cohort study. Obes Res Clin Pract . 2022;16(3):235-241. doi:10.1016/j.orcp.2022.04.002 Abramiuk M, Mertowska P, Frankowska K, et al. How can selected dietary ingredients influence the development and progression of endometriosis? Nutrients . 2024;16(1):154. doi:10.3390/nu16010154 Yang Q, Zheng J, Chen W, et al. Association between preadmission metformin use and outcomes in intensive care unit patients with sepsis and type 2 diabetes: a cohort study. Front Med . 2021;8:640785. doi:10.3389/fmed.2021.640785 Fuldeore MJ, Soliman AM. Prevalence and symptomatic burden of diagnosed endometriosis in the United States: national estimates from a cross-sectional survey of 59,411 women. Gynecol Obstet Invest . 2017;82(5):453-461. doi:10.1159/000452660 Christ JP, Yu O, Schulze-Rath R, Grafton J, Hansen K, Reed SD. Incidence, prevalence, and trends in endometriosis diagnosis: a united states population-based study from 2006 to 2015. Am J Obstet Gynecol . 2021;225(5):500.e1-500.e9. doi:10.1016/j.ajog.2021.06.067 Voltolini Velho R, Halben N, Chekerov R, et al. Functional changes of immune cells: signal of immune tolerance of the ectopic lesions in endometriosis? Reprod Biomed Online . 2021;43(2):319-328. doi:10.1016/j.rbmo.2021.04.012 Nasiadek M, Stragierowicz J, Klimczak M, Kilanowicz A. The role of zinc in selected female reproductive system disorders. Nutrients . 2020;12(8):2464. doi:10.3390/nu12082464 Cirillo M, Argento FR, Becatti M, Fiorillo C, Coccia ME, Fatini C. Mediterranean Diet and Oxidative Stress: A Relationship with Pain Perception in Endometriosis. Int J Mol Sci . 2023;24(19):14601. doi:10.3390/ijms241914601 Cirillo M, Argento FR, Attanasio M, et al. Atherosclerosis and Endometriosis: The Role of Diet and Oxidative Stress in a Gender-Specific Disorder. Biomedicines . 2023;11(2):450. doi:10.3390/biomedicines11020450 Zhang M, Xu T, Tong D, et al. Research advances in endometriosis-related signaling pathways: A review. Biomed Pharmacother . 2023;164:114909. doi:10.1016/j.biopha.2023.114909 Table 1 and 2 Table 1 and 2 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Table1and2.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 25 Aug, 2025 Editor invited by journal 31 Jul, 2025 Editor assigned by journal 24 Jul, 2025 Submission checks completed at journal 24 Jul, 2025 First submitted to journal 22 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-7188235","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":506390526,"identity":"63b0f974-7728-44d0-a793-1f196d33fccc","order_by":0,"name":"Qian Xue","email":"","orcid":"","institution":"People’s Hospital of Leshan","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Qian","middleName":"","lastName":"Xue","suffix":""},{"id":506390527,"identity":"28f2e844-7077-4993-92d1-bda114663967","order_by":1,"name":"Hongju Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA70lEQVRIiWNgGAWjYDACCQYGZhDN2MD//eOHCgk5eRK0MJgxS5yxMDZsIFYLEJgx8LZVJDIcIKCDf3bzsccFFXfsmmckpD2QnCeRwNjA/PDRDXyW3DmWbjzjzLPkxhkJxw0Kt0nksTOwGRvn4NFiIJFjJs3bdjiZsedgg4TkNolixgYeNmn8WvK/QbUcZpDgnSOR2HCAoJYcNpAWO8b2NjYJ3gYitEjcSDOT5jlzOIGxvYfZWOKYhLFhMwG/8M9IfibNU3HY3rCZh/Hhh5o6OXn25oeP8WmBgcSNDTAmMx5lyMCecDoZBaNgFIyCEQsASw5In3dXy68AAAAASUVORK5CYII=","orcid":"","institution":"Leshan Hospital of Traditional Chinese Medicine","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Hongju","middleName":"","lastName":"Chen","suffix":""}],"badges":[],"createdAt":"2025-07-22 14:38:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7188235/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7188235/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":90471116,"identity":"87fdd8c3-22b7-459a-9fe2-d10764177b48","added_by":"auto","created_at":"2025-09-03 06:21:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":477669,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7188235/v1/fb690fe43d9eb7b4dd13350a.png"},{"id":90470116,"identity":"a8d1c36f-5f95-4fc5-a7b0-e7dc6ecfb569","added_by":"auto","created_at":"2025-09-03 06:13:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1391223,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7188235/v1/dd1395dbe7bdc15bdbdb4c9b.png"},{"id":90470118,"identity":"da67ddb6-8619-4d18-9bd5-6955dac61091","added_by":"auto","created_at":"2025-09-03 06:13:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":483029,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7188235/v1/d14b29bfa653611cafd9bfd1.png"},{"id":90471119,"identity":"dc0e8441-c667-4d28-880d-402c92311143","added_by":"auto","created_at":"2025-09-03 06:21:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2896776,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7188235/v1/26925292-913d-4eaa-b3a9-382526925048.pdf"},{"id":90470115,"identity":"da23c337-b6a2-4e0d-aba4-733f2b268584","added_by":"auto","created_at":"2025-09-03 06:13:08","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":24437,"visible":true,"origin":"","legend":"","description":"","filename":"Table1and2.docx","url":"https://assets-eu.researchsquare.com/files/rs-7188235/v1/604893f9e265622001a945d5.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Association of dietary folate intake with endometriosis in US participants :a retrospective cross-sectional study","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eEndometriosis is a challenging gynecological disease to treat. Although it is a benign condition, it shares biological characteristics with malignant tumors. Endometriosis involves the presence of endometrium-like tissue outside the uterine cavity, such as in the pelvis or vagina\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. The complications it causes can lead to infertility, dysmenorrhea, and chronic pelvic pain\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, significantly affecting a woman's quality of life.Endometriosis primarily causes pelvic pain symptoms, which can lead to decreased fertility. Nearly half of endometriosis patients experience significantly reduced fertility, and up to two-thirds of women with dysmenorrhea suffer from the condition. Additionally, about three-quarters of endometriosis patients report chronic pelvic pain \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Due to its prevalence and impact on women's health, endometriosis is considered a significant public health issue. However, the cause of endometriosis is not yet fully understood, and research is ongoing to identify modifiable risk factors for its development.\u003c/p\u003e\u003cp\u003eFolate, also known as vitamin B9, is a crucial nutrient that plays essential roles in various physiological functions, such as neurotransmitter production, DNA synthesis, and cell division\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Folate also has anti-inflammatory properties, reduces oxidative stress, and plays an immunomodulatory role\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eA series of studies have shown that folate plays a significant role in women's reproductive health. Research by Liu, P, et al. indicates that folate and other micronutrients may reduce the risk of endometriosis by decreasing the inflammatory response\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Another study highlighted abnormalities in folate metabolism in infertile patients with endometriosis, emphasizing the importance of adequate folate levels in improving endometriosis symptoms and infertility\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Additionally, one study examined the relationship between folate intake and the risk of ovarian cancer in women with endometriosis\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe core objective of this study is to explore in depth the possible association between daily dietary intake of folate and endometriosis in women aged 20 to 54 in the United States. We aim to enhance endometriosis prevention and treatment through this research, contributing to new advancements in the field of women's health.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Study population\u003c/h2\u003e\u003cp\u003eData for the study were collected by NHANES, which is a cross-sectional, population-based survey conducted by the National Center for Health Statistics. The survey utilizes a nationally representative, stratified sample, which is based on interviews and physical examinations.The data for this study were derived from four two-year NHANES cycles conducted between 1999 and 2006. Reproductive health survey information was included in these cycles. A total of 15,886 female participants were recruited after screening, but women aged under 20 years or over 54 years were excluded,those with missing endometriosis-related information, missing data on dietary folate intake, pregnant women, and those with missing data on covariates were also excluded. In total, 4,024 women were included in the study, 321 with endometriosis and 3,703 without.In this study, all methods were performed in strict compliance with relevant guidelines and regulations to ensure the scientific and standardised nature of the study. Prior to participation in NHANES, participants signed a written informed consent form in order to safeguard their rights and privacy, and in addition, the data were made publicly available on the NHANES website ( \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://www.cdc.gov/nchs/nhanes.htm\u003c/span\u003e\u003cspan address=\"http://www.cdc.gov/nchs/nhanes.htm\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Endometriosis assessment\u003c/h2\u003e\u003cp\u003eTo identify participants with endometrial disease, we looked at their responses to the question in the reproductive health section of the questionnaire, \"Have you ever been told by a doctor or other health care professional that you have endometriosis?\"\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Dietary folate intake\u003c/h2\u003e\u003cp\u003eDietary folate intake, referring to the daily dietary intake of total folate, was accurately calculated from the NHANES 24-hour food recall questionnaire, which detailed the types and amounts of food consumed by the subjects\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e, as well as from thedietary interview procedure manual\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Participants were categorized into quartiles (Q1-Q4) based on their dietary folate intake. According to the World Health Organization's recommended daily intake of 400 \u0026micro;g of folate, the participants were divided into two groups: the folate deficiency group, with an intake of less than 400 \u0026micro;g, and the folate adequate group, with an intake of greater than or equal to 400 \u0026micro;g.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Covariates\u003c/h2\u003e\u003cp\u003eTo ensure the accuracy of the research analysis, this study included as many relevant variables as possible. The variables analyzed were age, race/ethnicity, education level, family poverty rate income (PIR), marital status, smoking status, physical activity, body mass index (BMI), and nutrients (energy, proteins, and carbohydrates).\u003c/p\u003e\u003cp\u003eRace/ethnicity was categorized as Non-Hispanic White, Non-Hispanic Black, Mexican American, or other race. Marital status was categorized as married/with a partner or alone. Education level was categorized based on the number of years of education received: less than 9 years, 9 to 12 years, or more than 12 years. Physical activity was classified as sedentary, moderate, or vigorous. Smoking status was categorized as never smokers, current smokers, and former smokers\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. BMI was calculated based on weight and height, and nutrient intake (energy, proteins, and carbohydrates) was calculated based on the NHANES 24-hour food recall questionnaire and dietary interview procedure manual.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Statistical analyses\u003c/h2\u003e\u003cp\u003eThis study analyzed NHANES data from 1999\u0026ndash;2006. Continuous variables conforming to normal distributions are expressed as mean (standard deviation), while skewed distributions are expressed as median (interquartile range). Categorical variables are expressed as proportions (%).Dietary folate intake was analyzed both as a continuous variable and as an interquartile categorical variable. Multivariate logistic regression was used to calculate 95% confidence intervals (CI) for the association between dietary folate intake and endometriosis. Restricted cubic spline plots were used to confirm the linear correlation between folate intake and endometriosis, with subgroup analyses conducted to determine whether other confounders interacted.\u003c/p\u003e\u003cp\u003eModel 1 is not adjusted. Model 2 is adjusted for demographic characteristics such as age, educational status, marital status, race/ethnicity, and family PIR. Xu et al. suggested that socio-economic and lifestyle factors are associated with the incidence of endometriosis \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Additionally, dietary intake, education, age, and family PIR may also affect total folate intake \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. Furthermore, marital status and race may influence dietary habits. A previous NHANES study found an association between smoking and endometriosis \u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, possibly due to cigarette smoke inducing oxidative stress. Rowlands et al. proposed that the risk of endometriosis is related to body weight \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. As a result, Model 3 is adjusted to include BMI, smoking status, and physical activity, in addition to the variables from Model 2. Abramiuk et al. conducted a literature review suggesting that dietary components influence the development and progression of endometriosis \u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, and three nutrients affect folate intake. Therefore, Model 4 incorporates the variables from Model 3, as well as adjustments for energy, protein consumption, and carbohydrate consumption.\u003c/p\u003e\u003cp\u003eThe statistical software program used for all analyses was R 3.3.2 (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://www.R-project.org\u003c/span\u003e\u003cspan address=\"http://www.R-project.org\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e, The R Foundation, Shanghai, China). Additionally, Free Statistics Software 1.9 (Beijing Free Clinical Medical Technology Co., LTD) was employed for data processing and analysis\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. A descriptive analysis was conducted for all participants. Results with p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 were considered statistically significant.\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results","content":"\u003cp\u003eThe study analyzed data from four NHANES periods (1999\u0026ndash;2006). A total of 15,886 women participated in the study. After excluding those with missing endometriosis data, the remaining 4,412 patients were aged 20 to 54 years and did not include pregnant women. Further exclusions were made for participants with missing covariates such as BMI, smoking status, physical activity, family PIR, marital status, and education, resulting in a total of 4,024 participants included in the analysis (Fig.\u0026nbsp;1).\u003c/p\u003e\n\u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the baseline characteristics of the 4,024 participants who completed the study, with a mean age of 37.4 years. Among these, 321 (8.0%) had endometriosis. Participants who were non-Hispanic white, had higher education levels, higher household PIR, did not smoke, had a lower BMI, and had greater access to energy, protein, and carbohydrates generally had higher dietary folate intakes. It was observed that patients with endometriosis had a lower intake of folate.\u003c/p\u003e\n\u003cdiv\u003eTo investigate the effect of dietary folate intake on endometriosis, we constructed four multivariate logistic regression models, using dietary folate as a continuous variable. In Model 1, total dietary folate intake was negatively associated with endometriosis (OR: 0.93, 95% CI: 0.88\u0026ndash;0.99, P\u0026thinsp;=\u0026thinsp;0.03). After adjustment for potential confounders in Model 4, total dietary folate intake remained negatively associated with endometriosis (OR: 0.92, 95% CI: 0.85-1, P\u0026thinsp;=\u0026thinsp;0.041), representing an 8% reduction in the risk of endometriosis for each 100 \u0026micro;g increase in folate. (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/div\u003e\n\u003cdiv\u003eWhen dietary folate was used as a categorical variable, it was divided into four quartiles: Q1 (0-206 \u0026micro;g), Q2 (207\u0026ndash;300 \u0026micro;g), Q3 (301\u0026ndash;429 \u0026micro;g), and Q4 (430\u0026ndash;2827 \u0026micro;g). In Model 1, compared to Q1, the ORs for Q2, Q3, and Q4 were 0.87, 0.81, and 0.69, respectively (p for trend\u0026thinsp;=\u0026thinsp;0.002). After adjustment for potential confounders in Model 4, the ORs of endometriosis for Q2, Q3, and Q4 compared with Q1 were 0.82 (95% CI: 0.59\u0026ndash;1.14), 0.75 (95% CI: 0.52\u0026ndash;1.08), and 0.63 (95% CI: 0.42\u0026ndash;0.96), respectively (p for trend\u0026thinsp;=\u0026thinsp;0.032).When grouped according to the internationally recommended folate intake of 400 \u0026micro;g per day, if the daily folate intake was greater than or equal to 400 \u0026micro;g, the risk of endometriosis was reduced by 35% in Model 1. This result remained stable in Models 2, 3, and 4, with the risk of endometriosis reduced by 37% (OR\u0026thinsp;=\u0026thinsp;0.63, 95% CI: 0.66\u0026ndash;0.86, P\u0026thinsp;=\u0026thinsp;0.003). These results suggest that the risk of endometriosis decreases with increasing dietary folate intake. (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/div\u003e\n\u003cp\u003eAs shown in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, dietary folate intake is correlated with endometriosis. To examine this association, we plotted a restricted cubic spline. The smooth plot in Fig.\u0026nbsp;2 shows a clear linear relationship (non-linear P\u0026thinsp;=\u0026thinsp;0.667) between dietary folate intake and the risk of endometriosis after adjusted for potential confounders. By excluding the top 0.3% of extreme outliers in dietary folate intake, the plot further confirms that the risk of endometriosis decreases with increasing dietary folic acid intake.(Fig.\u0026nbsp;2)\u003c/p\u003e\n\u003cp\u003eSubgroup analyses were conducted to further investigate the relationship between dietary folate intake and endometriosis. Age was divided into two groups with a cutoff at 40 years, and BMI was divided into two groups with a cutoff at 30 kg/m\u0026sup2;. Stratified regression models were used to analyze the data based on age, race, marital status, educational level, family PIR, physical activity, smoking status, and BMI. The forest plot (Fig.\u0026nbsp;3) indicated no statistically significant interactions between dietary folic acid intake and these subgroups in the association with endometriosis (P values for interaction were all \u0026gt;\u0026thinsp;0.05). (Fig.\u0026nbsp;3)\u003c/p\u003e"},{"header":"4 Comment","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e4.1 Principal Findings\u003c/h2\u003e\u003cp\u003eThe study was cross-sectional and involved 4,024 participants, of whom 8.0% had endometriosis (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The prevalence of endometriosis in the US ranges from 6.1–8.9%\u003csup\u003e20,21\u003c/sup\u003e, which is consistent with our findings. Additionally, there was a negative relationship between endometriosis and dietary folate intake in US women aged 20–54 years. Participants with higher folate intake had a lower risk of endometriosis (OR: 0.63; 95% CI: 0.42–0.96) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The restricted cubic spline plots further supported a significant linear relationship between folate intake and endometriosis (Fig.\u0026nbsp;2). Based on these findings, it appears that increased folate intake may reduce the prevalence of endometriosis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e4.2 Results in the Context of What is Known\u003c/h2\u003e\u003cp\u003eEndometriosis is a common gynecological condition with unknown etiology, risk factors, and effective treatments. The development of endometriosis involves a complex interplay of mechanisms that are not yet fully understood. Multiple factors such as oxidative stress, cytokine regulation, and prostaglandins are involved in the pathogenesis of endometriosis\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. Modulation of the immune system and inflammatory cytokines has been implicated in the development of endometriosis by Voltolini et al.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Further research is urgently required to gain a deeper understanding of the pathogenesis of endometriosis and to facilitate the discovery of improved treatment options.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e4.3 Clinical Implications and Research Implications\u003c/h2\u003eFolate may reduce the risk of endometriosis through several mechanisms:\u003cp\u003e\u003cstrong\u003eAnti-inflammatory effects\u003c/strong\u003e: Folate may help reduce inflammation, a key feature of endometriosis. By reducing markers of inflammation, folate could potentially alleviate some of the symptoms associated with this condition. A study evaluating the effects of a Mediterranean diet, which included folate, on endometriosis showed that an anti-inflammatory diet could help alleviate the symptoms of endometriosis\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eReduces oxidative stress\u003c/strong\u003e: The development of endometriosis is associated with increased oxidative stress. Folate, through its role in homocysteine metabolism, can help reduce oxidative stress and protect cells from damage. A study has shown that increased intake of folate may help reduce cellular oxidative stress and alleviate the symptoms of endometriosis\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eImmunomodulation\u003c/strong\u003e: Folate has been suggested to have immunomodulatory effects, which may help reduce immune dysfunction in patients with endometriosis. Zhang, M et al. studied endometriosis-related signaling pathways and their immunomodulation, highlighting the role of folate in regulating abnormal immune responses \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e4.4 Strengths and Limitations\u003c/h2\u003e\n \u003cp\u003eThe study has several strengths: first, a robust data base: Analysing data from 4,024 participants through the reliable National Health and Nutrition Examination Survey (NHANES) database, with accurate dietary assessment through a 24-hour food recall system, provided a substantial and accurate foundation for investigating the association between dietary folate intake and endometriosis.Second, rigorous and controlled analysis: Adjusted for multiple confounding variables and demonstrated consistency across different populations, ensuring a robust analysis of the association between folate intake and endometriosis risk.Third, threshold effect identification: Identifying a specific threshold (400 µg of daily folate intake) associated with a reduced risk of endometriosis, providing practical implications for dietary recommendations.Finally,Novel insights and contributions: Providing new insights into the potential role of folate in the pathogenesis of endometriosis and the potential benefits of dietary folate intake for women's reproductive health, contributing to the limited existing research in this area.\u003c/p\u003e\n \u003cp\u003eThere are some limitations in this study that should be noted. First, the study's sample group was limited to American women aged 20 to 54, so the results may not be directly applicable to women of other races or countries. Second, the diagnosis of endometriosis relied primarily on a single question in the questionnaire, rather than the international standard classification of endometriosis diagnoses, which may affect diagnostic accuracy. Additionally, the accuracy and reliability of the dietary assessment were impacted by potential recall bias inherent in the 24-hour recall method, which may have introduced some bias into the study results. To more fully assess the association between folate and endometriosis, future studies using a prospective cohort design are needed to further clarify the causal relationship between folate intake and endometriosis.\u003c/p\u003e\n\u003c/div\u003e\n"},{"header":"Conclusion","content":"\u003cp\u003eThis study found that dietary folate intake was inversely associated with endometriosis among in US adults. Ensuring adequate intake of folate in the diet may help reduce the risk of endometriosis or alleviate its symptoms.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank all all the staff and participants in NHAENS 1999-2006 for their contribution in the form of donations, data collection and data sharing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eFunding information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grants from public, commercial or voluntary funding bodies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no competing interests.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePublic datasets used in this study. The names of the repositories and their accession numbers can be found at http://www.cdc.gov/ nchs/nhanes.htm (accessed: 8 Feb 2025).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eEthical Compliance\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study used de-identified NHANES data, which received institutional review board (IRB) approval. \u0026nbsp;All participants provided informed consent, and analyses adhered to NHANES analytic guidelines.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZondervan KT, Becker CM, Koga K, Missmer SA, Taylor RN, Vigan\u0026ograve; P. Endometriosis. \u003cem\u003eNat Rev Dis Primer\u003c/em\u003e. 2018;4(1):9. doi:10.1038/s41572-018-0008-5\u003c/li\u003e\n\u003cli\u003eJohnson NP, Hummelshoj L, Adamson GD, et al. World Endometriosis Society consensus on the classification of endometriosis. \u003cem\u003eHum Reprod\u003c/em\u003e. 2017;32(2):315-324. doi:10.1093/humrep/dew293\u003c/li\u003e\n\u003cli\u003eGiampaolino P, Della Corte L, Foreste V, Barra F, Ferrero S, Bifulco G. Dioxin and endometriosis: a new possible relation based on epigenetic theory. \u003cem\u003eGynecol Endocrinol\u003c/em\u003e. 2020;36(4):279-284. doi:10.1080/09513590.2019.1698024\u003c/li\u003e\n\u003cli\u003eNeurock M, Janik M, Wieckowski A. A first principles comparison of the mechanism and site requirements for the electrocatalytic oxidation of methanol and formic acid over Pt. \u003cem\u003eFaraday Discuss\u003c/em\u003e. 2009;140:363-378. doi:10.1039/B804591G\u003c/li\u003e\n\u003cli\u003eDem\u0026eacute;zio Da Silva CV, Felipe VL, Shivappa N, et al. Dietary inflammatory index score and risk of developing endometriosis: a case\u0026ndash;control study. \u003cem\u003eJ Endometr Pelvic Pain Disord\u003c/em\u003e. 2021;13(1):32-39. doi:10.1177/2284026520967599\u003c/li\u003e\n\u003cli\u003eLiu P, Maharjan R, Wang Y, et al. Association between dietary inflammatory index and risk of endometriosis: a population-based analysis. \u003cem\u003eFront Nutr\u003c/em\u003e. 2023;10:1077915. doi:10.3389/fnut.2023.1077915\u003c/li\u003e\n\u003cli\u003eGuedes T, Santos AA, Vieira-Neto FH, Bianco B, Barbosa CP, Christofolini DM. Folate metabolism abnormalities in infertile patients with endometriosis. \u003cem\u003eBiomark Med\u003c/em\u003e. 2022;16(7):549-557. doi:10.2217/bmm-2021-0076\u003c/li\u003e\n\u003cli\u003eGersekowski K, Ibiebele TI, for the Australian Ovarian Cancer Study Group, et al. Folate intake and ovarian cancer risk among women with endometriosis: a case\u0026ndash;control study from the ovarian cancer association consortium. \u003cem\u003eCancer Epidemiol Biomarkers Prev\u003c/em\u003e. 2023;32(8):1087-1096. doi:10.1158/1055-9965.EPI-23-0121\u003c/li\u003e\n\u003cli\u003ePrentice RL, Mossavar-Rahmani Y, Huang Y, et al. Evaluation and comparison of food records, recalls, and frequencies for energy and protein assessment by using recovery biomarkers. \u003cem\u003eAm J Epidemiol\u003c/em\u003e. 2011;174(5):591-603. doi:10.1093/aje/kwr140\u003c/li\u003e\n\u003cli\u003eSubar AF. Using intake biomarkers to evaluate the extent of dietary misreporting in a large sample of adults: the OPEN study. \u003cem\u003eAm J Epidemiol\u003c/em\u003e. 2003;158(1):1-13. doi:10.1093/aje/kwg092\u003c/li\u003e\n\u003cli\u003eUnited States Department of Agriculture (USDA), Agriculture Research Service FSRG. Food and Nutrient Database for Dietary Studies, 5.0. Accessed Mayr 8, 2024. http://www.ars.usda. gov/ba/bhnrc/fsrg\u003c/li\u003e\n\u003cli\u003eNational Health and Nutrition Examination Survey (NHANES). MEC In-Person Dietary Interviewers Procedures Manual. Accessed May 8, 2024. http://www.cdc.gov/nchs/data/nhanes/nhanes_03_04/dietary_mec.pdf\u003c/li\u003e\n\u003cli\u003eHuang W, Ma X, Liang H, et al. Dietary magnesium intake affects the association between serum vitamin D and type 2 diabetes: a cross-sectional study. \u003cem\u003eFront Nutr\u003c/em\u003e. 2021;8:763076. doi:10.3389/fnut.2021.763076\u003c/li\u003e\n\u003cli\u003eXu G, Chen L, Li Q. Association of iron metabolism markers, socioeconomic and lifestyle factors with endometriosis: A cross-sectional study. \u003cem\u003eJ Trace Elem Med Biol\u003c/em\u003e. 2023;78:127175. doi:10.1016/j.jtemb.2023.127175\u003c/li\u003e\n\u003cli\u003eGibson RS, Anderson VP. A review of interventions based on dietary diversification or modification strategies with the potential to enhance intakes of total and absorbable zinc. \u003cem\u003eFood Nutr Bull\u003c/em\u003e. 2009;30(1_suppl1):S108-S143. doi:10.1177/15648265090301S107\u003c/li\u003e\n\u003cli\u003eKim H, Lee H, Kazmi S, et al. Familial risk for endometriosis and its interaction with smoking, age at menarche and body mass index: a population‐based cohort study among siblings. \u003cem\u003eBjog- Int J Obstet Gynaecol\u003c/em\u003e. 2021;128(12):1938-1948. doi:10.1111/1471-0528.16769\u003c/li\u003e\n\u003cli\u003eRowlands IJ, Hockey R, Abbott JA, Montgomery GW, Mishra GD. Body mass index and the diagnosis of endometriosis: findings from a national data linkage cohort study. \u003cem\u003eObes Res Clin Pract\u003c/em\u003e. 2022;16(3):235-241. doi:10.1016/j.orcp.2022.04.002\u003c/li\u003e\n\u003cli\u003eAbramiuk M, Mertowska P, Frankowska K, et al. How can selected dietary ingredients influence the development and progression of endometriosis? \u003cem\u003eNutrients\u003c/em\u003e. 2024;16(1):154. doi:10.3390/nu16010154\u003c/li\u003e\n\u003cli\u003eYang Q, Zheng J, Chen W, et al. Association between preadmission metformin use and outcomes in intensive care unit patients with sepsis and type 2 diabetes: a cohort study. \u003cem\u003eFront Med\u003c/em\u003e. 2021;8:640785. doi:10.3389/fmed.2021.640785\u003c/li\u003e\n\u003cli\u003eFuldeore MJ, Soliman AM. Prevalence and symptomatic burden of diagnosed endometriosis in the United States: national estimates from a cross-sectional survey of 59,411 women. \u003cem\u003eGynecol Obstet Invest\u003c/em\u003e. 2017;82(5):453-461. doi:10.1159/000452660\u003c/li\u003e\n\u003cli\u003eChrist JP, Yu O, Schulze-Rath R, Grafton J, Hansen K, Reed SD. Incidence, prevalence, and trends in endometriosis diagnosis: a united states population-based study from 2006 to 2015. \u003cem\u003eAm J Obstet Gynecol\u003c/em\u003e. 2021;225(5):500.e1-500.e9. doi:10.1016/j.ajog.2021.06.067\u003c/li\u003e\n\u003cli\u003eVoltolini Velho R, Halben N, Chekerov R, et al. Functional changes of immune cells: signal of immune tolerance of the ectopic lesions in endometriosis? \u003cem\u003eReprod Biomed Online\u003c/em\u003e. 2021;43(2):319-328. doi:10.1016/j.rbmo.2021.04.012\u003c/li\u003e\n\u003cli\u003eNasiadek M, Stragierowicz J, Klimczak M, Kilanowicz A. The role of zinc in selected female reproductive system disorders. \u003cem\u003eNutrients\u003c/em\u003e. 2020;12(8):2464. doi:10.3390/nu12082464\u003c/li\u003e\n\u003cli\u003eCirillo M, Argento FR, Becatti M, Fiorillo C, Coccia ME, Fatini C. Mediterranean Diet and Oxidative Stress: A Relationship with Pain Perception in Endometriosis. \u003cem\u003eInt J Mol Sci\u003c/em\u003e. 2023;24(19):14601. doi:10.3390/ijms241914601\u003c/li\u003e\n\u003cli\u003eCirillo M, Argento FR, Attanasio M, et al. Atherosclerosis and Endometriosis: The Role of Diet and Oxidative Stress in a Gender-Specific Disorder. \u003cem\u003eBiomedicines\u003c/em\u003e. 2023;11(2):450. doi:10.3390/biomedicines11020450\u003c/li\u003e\n\u003cli\u003eZhang M, Xu T, Tong D, et al. Research advances in endometriosis-related signaling pathways: A review. \u003cem\u003eBiomed Pharmacother\u003c/em\u003e. 2023;164:114909. doi:10.1016/j.biopha.2023.114909\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table 1 and 2","content":"\u003cp\u003eTable 1 and 2 are available in the Supplementary Files section.\u003c/p\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"bmc-womens-health","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmwh","sideBox":"Learn more about [BMC Women's Health](http://bmcwomenshealth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bmwh/default.aspx","title":"BMC Women's Health","twitterHandle":"","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"dietary folate intake, endometriosis, NHANES","lastPublishedDoi":"10.21203/rs.3.rs-7188235/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7188235/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e\u003cp\u003eTo investigate the dose-response relationship between dietary folate intake and endometriosis risk among U.S. women of reproductive age.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eThis cross-sectional study analyzed 4,024 women (aged 20\u0026ndash;54 years) from the 1999\u0026ndash;2006 NHANES cycles. Dietary folate intake was quantified via 24-hour recall and categorized into quartiles (Q1-Q4: 0\u0026ndash;206, 207\u0026ndash;300, 301\u0026ndash;429, and 430\u0026ndash;2,827 \u0026micro;g/day). Multivariable logistic regression models adjusted for sociodemographics, lifestyle factors, and dietary confounders evaluated the folate-endometriosis association. Restricted cubic splines assessed nonlinear trends.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eAmong participants, 8.0% (321/4,024) reported endometriosis. Higher folate intake exhibited a dose-dependent inverse association with endometriosis risk. Compared to Q1 (reference), adjusted odds ratios (95% CI) for Q2\u0026ndash;Q4 were 0.82 (0.59\u0026ndash;1.14), 0.75 (0.52\u0026ndash;1.08), and 0.63 (0.42\u0026ndash;0.96), respectively (P for trend\u0026thinsp;=\u0026thinsp;0.032). A linear threshold effect was observed, with intake\u0026thinsp;\u0026ge;\u0026thinsp;400 \u0026micro;g/day associated with 37% reduced risk (OR\u0026thinsp;=\u0026thinsp;0.63, 95% CI:0.46\u0026ndash;0.86; P\u0026thinsp;=\u0026thinsp;0.003). Subgroup analyses revealed no significant interactions by age, BMI, or lifestyle factors (P interaction\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eDietary folate intake demonstrates a significant inverse linear relationship with endometriosis risk in U.S. women, suggesting adequate folate consumption (\u0026ge;\u0026thinsp;400 \u0026micro;g/day) may mitigate disease burden.\u003c/p\u003e","manuscriptTitle":"Association of dietary folate intake with endometriosis in US participants :a retrospective cross-sectional study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-03 06:13:04","doi":"10.21203/rs.3.rs-7188235/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2025-08-25T12:55:27+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-07-31T09:51:34+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-24T08:52:39+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-24T08:51:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Women's Health","date":"2025-07-22T14:27:46+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-womens-health","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmwh","sideBox":"Learn more about [BMC Women's Health](http://bmcwomenshealth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/bmwh/default.aspx","title":"BMC Women's Health","twitterHandle":"","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f4b1dfb5-02a3-4006-a1af-dc4ec98237a5","owner":[],"postedDate":"September 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-09-03T06:13:04+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-03 06:13:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7188235","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7188235","identity":"rs-7188235","version":["v1"]},"buildId":"cBFmMYwuxLRRLfASyISRj","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}