Female mice injected with low doses of bisphenol A experienced both a decline in fertility and in the number of pups in their litters after their first pregnancy, according to a study conducted by a research team at Tufts University School of Medicine in Boston.
The findings, published online Dec. 2 in the scientific journal Environmental Health Perspectives, also suggest an increased risk of breast and prostate cancers, obesity and more masculine behavior in female mice from doses of BPA as low as 25 nanograms/kilogram.
Perinatal exposure to BPA leads to a dose-dependent decline in the reproductive capacity of female mice, said the report. The effects on the cumulative number of pups are comparable to those previously reported in mice developmentally exposed to diethylstilbestrol, a compound well known to impair reproduction in women. This association suggests the possibility that early BPA exposure may also impact reproductive capacity in women.
What's more, since its research found that the reduced fertility doesn't manifest itself until after the first pregnancy, the research team said a more sensitive test should be adopted by federal agencies to measure the true risks of endocrine disruptors such as BPA on fertility.
The team was led by Ana Soto, a medical doctor and professor at Tufts affiliated with its cellular, molecular and developmental biology program.
In addition, the team said some effects seen at low doses are not observed at much higher doses, so the practice of testing chemicals at very high doses might not reliably predict the hazards posed by low doses of endocrine-disrupting chemicals such as BPA.
However, Steve Hentges, executive director of the polycarbonate/BPA global group of the American Chemistry Council in Wash- ington, said the findings are of unclear relevance to human health because of the non-standard approach of injecting the mice.
A significant limitation of the study is that the laboratory animals were injected with BPA, which is of limited relevance to human health [because] people are primarily exposed to BPA through the diet [and] BPA is rapidly metabolized and eliminated from the body after oral exposure, said Hentges. Reproduction studies conducted according to internationally accepted guidelines have consistently concluded that BPA does not affect fertility at any dose relevant to human exposures.
Specifically, the Tufts study funded in part with a grant from the National Institute of Environmental Health Sciences found that perinatal exposure to BPA resulted in a decline in reproductive capacity [and] a significant decrease in the cumulative number of pups in the mice that were injected with BPA, compared with the control group.
These effects are consistent with previously reported alterations in the ovary, uterus, hypothalamus and pituitary from endocrine disrupters. Therefore, all these BPA-associated alterations undoubtedly contribute to the diminished reproductive outcome observed here.
The study comes just five weeks after a study by the Oakland, Calif.-based Kaiser Permanente Division of Research found a link between decreased sperm count and BPA in the urine of 218 Chinese factory workers.
Many studies have linked BPA to potential health and reproductive problems in animals. But many governments and agencies worldwide continue to assert that BPA is safe, including the U.S., the European Food Safety Authority and the World Health Organization.
Levels of BPA in the human body are very low, indicating that BPA is not accumulated in the body and is rapidly eliminated through urine, said WHO, which had convened an international panel of experts in Ottawa, Ontario, to assess BPA safety.
In addition, a peer-reviewed study in November said BPA levels found in canned food as well as fresh foods wrapped in plastic packaging in the U.S. have nearly 1,000 times less of the tolerable daily intake levels set by the Environmental Protection Agency and EFSA.
Still, in late November, the European Commission imposed a ban on PC baby bottles that contain BPA starting in June. Canada had imposed a similar ban two years ago, and baby bottle manufacturers that sell into the U.S. market said in 2009 they would stop selling baby bottles that contain BPA.
Canada declared BPA a toxic substance Oct. 13 and is developing regulations to manage risks.
In the U.S., bans on BPA baby bottles have been passed in seven states, Chicago and four New York counties.