Context: Experimental data in rodents suggest that the adverse reproductive health effects of bisphenol A (BPA) can be modified by intake of soy phytoestrogens. Whether the same is true in humans is not known.
Objective: The purpose of this study was to evaluate whether soy consumption modifies the relation between urinary BPA levels and infertility treatment outcomes among women undergoing assisted reproduction.
Setting: The study was conducted in a fertility center in a teaching hospital.
Design: We evaluated 239 women enrolled between 2007 and 2012 in the Environment and Reproductive Health (EARTH) Study, a prospective cohort study, who underwent 347 in vitro fertilization (IVF) cycles. Participants completed a baseline questionnaire and provided up to 2 urine samples in each treatment cycle before oocyte retrieval. IVF outcomes were abstracted from electronic medical records. We used generalized linear mixed models with interaction terms to evaluate whether the association between urinary BPA concentrations and IVF outcomes was modified by soy intake.
Main outcome measure: Live birth rates per initiated treatment cycle were measured.
Results: Soy food consumption modified the association of urinary BPA concentration with live birth rates (P for interaction = .01). Among women who did not consume soy foods, the adjusted live birth rates per initiated cycle in increasing quartiles of cycle-specific urinary BPA concentrations were 54%, 35%, 31%, and 17% (P for trend = .03). The corresponding live birth rates among women reporting pretreatment consumption of soy foods were 38%, 42%, 47%, and 49% (P for trend = 0.35). A similar pattern was found for implantation (P for interaction = .02) and clinical pregnancy rates (P for interaction = .03) per initiated cycle, where urinary BPA was inversely related to these outcomes among women not consuming soy foods but unrelated to them among soy consumers.
Conclusion: Soy food intake may protect against the adverse reproductive effects of BPA. As these findings represent the first report suggesting a potential interaction between soy and BPA in humans, they should be further evaluated in other populations.