The association between vitamin intake and endometriosis: a cross-sectional study of the NHANES 1999–2006

Endometriosis is a common cause of female reproductive problems, and vitamin intake may affect its incidence. Therefore, we further explored the association between multivitamin intake and endometriosis in a large population-based study. This study included 3351 participants from the National Health and Nutrition Examination Survey (NHANES) 1999–2006. The dietary intake of eight vitamins was calculated as the average of two 24-h recall interviews, and information on endometriosis was obtained through questionnaires that included gynecological history. Multiple logistic regression analysis was used to explore the relationship between multivitamin intake and endometriosis. Smoothed curve fitting analysis was employed to assess the dose–response relationship between vitamins and endometriosis. Finally, subgroup analysis and interaction tests were conducted to determine the association of covariates between vitamins and endometriosis. In this large-scale cross-sectional study, multiple logistic regression analysis showed that the intake of vitamins A, B1, B2, B6, C and folate was negatively associated with the occurrence of endometriosis. The odds ratios associated with a per-SD increase were 0.836 (95%CI: 0.702, 0.997), 0.817 (95%CI: 0.702, 0.951), 0.860 (95%CI: 0.746, 0.991), 0.784 (95%CI: 0.669, 0.919), 0.845 (95%CI: 0.718, 0.994), and 0.772 (95%CI: 0.660, 0.903), respectively. Smoothed curve fitting analysis revealed that the intake of vitamins A, B1, B2, B6, C, and folate was negatively associated with the risk of endometriosis (P < 0.05). Vitamin E showed a saturating effect, with an optimal cutoff point at 13.18. Below this cutoff, the intake of vitamin E was negatively correlated with the risk of endometriosis (OR = 0.947, 95% CI: 0.906, 0.989), whereas above the cutoff, there was no significant correlation between vitamin E intake and the risk of endometriosis (OR = 1.001, 95% CI: 0.997, 1.005). The results of this study indicate a significant linear negative correlation between the intake of vitamins A, B1, B2, B6, C, and folate, and the risk of endometriosis, and reveal a threshold effect for vitamin E intake on the risk of endometriosis. These findings could inform clinical dietary interventions and may support the development of preventive strategies for endometriosis, potentially aiding in its reduction.