Regular soy intake may protect women undergoing infertility treatment from low success rates associated with bisphenol A (BPA) exposure, data published in the Journal of Clinical Endocrinology & Metabolism suggest.
“Our study is the first to show a possible interaction between soy and BPA in humans,” study researcher Jorge E. Chavarro, MD, ScD, of Harvard T.H. Chan School of Public Health, Brigham and Women’s Hospital, and Harvard Medical School in Boston, said in a press release.
“This is consistent with research in mice that found a soy-rich diet could protect against reproductive health problems associated with BPA exposure. More research is needed to determine why soy has this effect in humans.”
According to background information in the article, BPA, an endocrine-disrupting chemical commonly found in plastics and other food containers, can mimic estrogen. Research in animals, most notably rats, also indicates that BPA may adversely affect fertility.
At the same time, experimental data suggest that dietary factors may mitigate these adverse effects.
In this study, the researchers sought to determine the relationship between BPA exposure, diet, and reproduction in participants in the Environment and Reproductive Health (EARTH) Study — an ongoing prospective cohort study designed to evaluate the role of environmental factors and nutrition in fertility.
A total of 239 women, aged 18 to 45, who underwent at least 1 in vitro fertilization (IVF) cycle at Massachusetts General Hospital Fertility Center from 2007 to 2012 were included in the study.
Participants completed a baseline lifestyle questionnaire that included questions about soy consumption and provided 2 urine samples in each treatment cycle before oocyte retrieval to analyze BPA exposure. Live birth rates per cycle served as the primary outcome.
Of all participants, 176 (70%) consumed soy foods, with a mean isoflavone intake of 3.4 mg per day. Women underwent an average of 1.5 treatment cycles: 168 (70%) underwent 1 treatment cycle, 44 (18%) underwent 2 cycles, and 27 (11%) underwent 3 or more cycles. Urinary BPA concentrations ranged from less than 0.4 mcg/L to 16.6 mcg/L, with a median concentration of 1.3 mcg/L. Some racial differences were noted among those who consumed soy (P=.08), according to the researchers, with white women having higher BPA concentrations than Asian women.
Results showed that eating soy foods appeared to alter the link between urinary BPA concentration and live birth rates (P for interaction=.01). Among women who did not eat soy foods, live birth rates decreased with increasing urinary BPA concentrations; adjusted live birth rates per increasing quartiles of urinary BPA were 54%, 35%, 31%, and 17% (P for trend=.03). In comparison, among women who reported eating soy foods before undergoing IVF, live birth rates were 38%, 42%, 47%, and 49% for increasing quartiles of urinary BPA (P for trend=.035).
Similarly, higher levels of urinary BPA were associated with lower implantation (P for interaction=.02) and clinical pregnancy rates (P for interaction =.03) per initiated cycle among women who did not eat soy foods, while no association between urinary BPA and these outcomes were found among women who ate soy foods.
The researchers noted that the study had several limitations. These included the study population, which was composed entirely of women undergoing infertility treatment with assisted reproduction, the inherent limitations of diet questionnaires, and the potential for misclassification of BPA on spot urine samples.
“Although it is recommended that women trying to get pregnant reduce their exposure to BPA, our findings suggest that diet may modify some of the risks of exposure to BPA, a chemical that is nearly impossible to completely avoid due to its widespread use,” senior study author Russ Hauser, MD, ScD, MPH, of Harvard T.H.
Chan School of Public Health, Massachusetts General Hospital, and Harvard Medical School in Boston, said in the release.
“Additional research could help identify other diet and lifestyle changes that may modify the effects of not only BPA exposure, but also exposure to other chemicals,” added Dr Chavarro. “In order to fully appreciate risks to human health, we need to design studies that adequately assess both diet and environmental chemical exposures.”