Relationship between dietary phytoestrogens and development of urinary incontinence in midlife women

Objective: Because exogenous estrogen treatment has been associated with a higher risk of urinary incontinence, our objective was to evaluate the longitudinal relationships of dietary phytoestrogen intakes (isoflavones, coumestans, and lignans) and the development of incontinence in midlife women transitioning through menopause. Methods: The Study of Women's Health Across the Nation (SWAN) Phytoestrogen Study was developed within SWAN, a community-based, multisite, multiracial/ethnic, prospective cohort study. SWAN interviewers administered a food consumption assessment at baseline and on follow-up visits 5 and 9. The SWAN Phytoestrogen Study created a phytonutrient database that allowed estimation of the usual daily intakes of four isoflavones, four lignans, and coumestrol. On an annual self-administered questionnaire, participants reported on the frequency and type of incontinence. We used discrete proportional hazards models to evaluate whether the estimated daily intake of each phytoestrogen class on the visit previous to the first report of incontinence was associated with the development of monthly or more incontinence versus remaining continent. Results: We found no association or patterns of association between developing any, stress, or urge incontinence and the reported daily dietary intake of isoflavones, coumestrol, and lignans on the visit previous to the onset of incontinence. Conclusions: The results of this longitudinal study provide important information to better understand estrogenlike substances in the continence mechanism of midlife women. Our study shows that neither high nor low dietary intakes of isoflavones, coumestrol, and lignans prevent stress or urge incontinence. Future studies should evaluate whether serum levels of phytoestrogens or their metabolites impact incontinence symptoms.