Posted by: Sarah Mosko
By Sarah (Steve) Mosko
Researchers are finding evidence for the first time that inadvertent exposure to BPA (bisphenol-A) in women of child-bearing age might hinder their fertility, and the levels of BPA involved are similar to that observed in the general U.S. population.
The synthetic chemical BPA has earned a solid reputation as an endocrine disruptor based on its estrogen-mimicking properties and documented health effects on lab animals exposed to even low, environmentally-relevant doses. Literally hundreds of animal studies have linked BPA to a wide spectrum of health concerns including obesity, diabetes, breast and prostate cancer, attention deficit hyperactivity disorder, low sperm counts and abnormal genital development.
Human exposure to BPA is known to be widespread – over 90 percent of the U.S. population show BPA in their urine – and stems from water bottles and other consumer items made of polycarbonate plastics, the epoxy lining of most food & beverage cans, dental sealants and thermal check register receipts. Ingestion is thought to be the primary route of exposure.
Discerning whether current levels of BPA exposure in humans carry the same health risks seen in animals is intrinsically difficult because of ethical prohibitions on intentionally exposing people to a potentially harmful substance and because of the hodgepodge of other industrial chemicals to which humans are exposed. However, preliminary reports have surfaced linking BPA to human female infertility.
A Harvard University study just published in April focused on women undergoing in vitro fertilizations (IVF) at a Massachusetts fertility clinic, measuring urinary BPA levels at successive IVF treatment cycles for correlation with success of embryonic implantation. In IVF, women take fertility drugs to stimulate production of eggs which are then harvested for fertilization with sperm in a laboratory dish before being transferred to the woman’s uterus. Whether or not implantation occurs successfully was assessed by following blood levels of the pregnancy hormone β-chorionic gonadotropin which begins surging within two weeks of conception.
The researchers measured embryonic implantations because the right balance of estrogen and progesterone is needed for successful implantation and because 50-75 percent of very early pregnancy losses are thought to result from failed implantation occurring before a woman even knows she’s been pregnant. Furthermore, BPA has previously been detected both in the fluid which bathes eggs still in the ovary and in amniotic fluid, which means exposure could occur as early as the time of conception.
Studying pregnancy achieved via IVF allowed the researchers to detect failed implantations that would be very difficult to measure in couples attempting to conceive naturally.
The key finding of the study was that implantation failure occurred more frequently the higher the level of BPA detected in the women’s urine. Women with the highest BPA levels had almost twice the odds of implantation failure as women with the lowest levels, even when the women’s ages and other factors affecting fertility were taken into account. Given that the concentrations of urinary BPA detected were similar to that reported by the Centers for Disease Control for women in the general U.S. population (geometric means of 1.53 μg/L and 1.97 μg/L, respectively), this means that any impact of BPA on fertility was occurring at environmentally-relevant doses. These findings parallel studies in mice showing that administering low doses of BPA hindered uterine implantation, resulting in reduced litter size.
Another recent human study honed in instead on possible effects of BPA on the quality of women’s eggs. Among women undergoing IVF at a reproductive center at the University of California at San Francisco, the likelihood of successful fertilization by sperm in a laboratory dish was lower when the eggs were from women with higher blood levels of BPA.
From this, the researchers concluded that inadvertent exposure to BPA somehow reduces egg quality. Studies in mice show that exposing young females to low-dosage BPA produces defective egg cells with the wrong number of chromosomes (i.e. aneuploidy).
The authors of these human studies emphasize that the findings are preliminary and that, even if they hold up, there is no guarantee they would generalize to women pursuing pregnancy through natural means. Women seeking treatment for infertility might, for example, be more sensitive to an endocrine disruptor like BPA. However, the findings are potentially important given that infertility rates are on the rise in the United States and other developed countries: roughly 10-15 percent of couples are infertile.
The Food and Drug Administration (FDA) finally announced on July 17 a ban on BPA limited to baby bottles and sippy cups. Although manufacturers of these childcare items had already eliminated BPA voluntarily, the main trade association for the plastics industry (the American Chemistry Council) requested a formal ban so as to eliminate confusion for consumers. At least 11 states, including California and New York, had already implemented their own restrictions on BPA in feeding products for children
In March, however, the FDA rejected a petition from the National Resources Defense Council to more globally ban BPA from all food contact uses, though the agency is reportedly still reviewing the chemical’s safety.
Women of child-bearing age who are concerned about their own exposure to BPA are left to fend for themselves for the time being.