The chemical bisphenol A (BPA) is an endocrine disruptor that is widely used in the manufacture of a variety of consumer products. Exposure to BPA in the general population is widespread with detectable urinary concentrations in more than 90% of individuals in a representative sample of US residents. BPA has weak estrogenic activity and has been shown to adversely affect fertility in animal models. Harvard University researchers recently evaluated whether the adverse effects on BPA could be negated by soy isoflavones.
For this study, 239 women undergoing in vitro fertilization (IVF) were enrolled between 2007 and 2012. Participants completed a baseline questionnaire and provided up to 2 urine samples in each treatment cycle before oocyte retrieval. At enrollment, a brief, nurse-administered questionnaire was used to collect data on demographics, medical history, and lifestyle. Participants also completed a detailed take home questionnaire with additional questions on lifestyle factors, reproductive health, and medical history. The questionnaire included a section querying the frequency of consumption of 15 soy-based foods.
The results showed that among women who did not consume soyfoods, the adjusted live birth rates per initiated cycle decreased in a stepwise fashion as urinary BPA concentrations increased. More specifically when going from urinary BPA quartiles 1 to 4, the rates were 54%, 35%, 31%, and 17% (P for trend = .03). In contrast, the corresponding live birth rates among women reporting pretreatment consumption of soyfoods were 38%, 42%, 47%, and 49% (P for trend= 0.35). The authors concluded that soyfood intake may protect against the adverse reproductive effects of BPA. Ordinarily, an epidemiologic study like this might not carry much weight because of the low isoflavone intake among the population. Intake among soy consumers was only 3.4 mg per day. However, there are animal data in support of the findings, which adds to the biological plausibility of the results.
Chavarro JE, Minguez-Alarcon L, Chiu YH, Gaskins AJ, Souter I, Williams PL, Calafat AM, and Hauser R. Soy intake modifies the relation between urinary bisphenol A concentrations and pregnancy outcomes among women undergoing assisted reproduction. J Clin Endocrinol Metab 2016:jc20153473.