A prospective cohort study of Vitamins B, C, E, and multivitamin intake and endometriosis.

Purpose: Diet is a potentially modifiable risk factor for endometriosis. It has been hypothesized that vitamins C, E, and the B vitamins may influence factors involved in the pathogenesis of endometriosis, such as oxidative stress and steroid hormone metabolism. In this large, prospective cohort study, we examined the relation between intake of vitamins C, E, the B vitamins, and the use of multivitamin supplements and diagnosis of endometriosis.

Methods: Data were collected from women in the Nurses' Health Study II between 1991 and 2005. Diet was assessed via food frequency questionnaire. Incidence rate ratios (RR) and 95% confidence intervals (CI) were estimated using time-varying Cox proportional hazards models.

Results: A total of 1383 incident cases of laparoscopically-confirmed endometriosis were observed among 70,617 women during 735,286 person years of follow-up. Intakes of thiamine (B1) (RR = 0.84, CI = 0.72-0.99; P-value, test for linear trend [P] = 0.04), folate (B9) (RR = 0.79, CI = 0.66-0.93; P = 0.003), vitamin C (RR = 0.81, CI = 0.68-0.95; P = 0.02), and vitamin E (RR = 0.70, CI = 0.59-0.83; P<0.0001) solely from food sources were inversely related to endometriosis diagnosis. However, intakes of these nutrients from supplements alone were unrelated to endometriosis.

Conclusion: Thiamine, folate, vitamin C, and vitamin E from food sources are inversely related to endometriosis risk. Our results suggest that the protective mechanism may not be related to the nutrients themselves but rather other components of foods rich in these micronutrients or factors correlated with diets high in these vitamin-rich foods.