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Male Mice Exposed to BPA in the Womb Grow up to be Less Masculine and Undesirable to Females

June 27, 2011

A new study has found that feeding bisphenol A (BPA), a chemical Americans suffer exposure to from food packaging, to pregnant mice affects the masculinity of the male offspring.

Bisphenol A is an industrial chemical used in the manufacture of plastics and as part of food and beverage packaging. The primary way Americans suffer exposure to BPA is through their diet due to chemical leeching from packaging into food and beverages.

Researchers from the University of Missouri-Columbia used two groups of mice for the study, one group exposed to BPA during gestation and nursing and another without exposure. From two weeks before a female’s breeding until weaning of baby mice at 25 days old, researchers fed the first group of female deer mice a dosage of BPA equivalent to the amount the U.S. Food and Drug Administration (FDA) considers a non-toxic dose and safe for mothers to ingest.

When the male baby mice reached maturity, researchers tested both groups of mice for their ability to find their way back to their home cage through a maze twice a day for one week. Male mice exposed to BPA had difficulty navigating the maze, operating in a random inefficient manner with many never finding their way home. In contrast, male mice not exposed to BPA consistently found their way home each time and over the course of the week even learned the most direct route to take.

They also tested how “attractive” the male mice were to female mice ready to breed. Female mice, some exposed to BPA and some not, all favored the non-BPA exposed males.

“The BPA-exposed deer mice in our study look normal; there is nothing obviously wrong with them. Yet, they are clearly different," said Cheryl Rosenfeld, associate professor in biomedical sciences in the College of Veterinary Medicine and investigator in the Bond Life Sciences Center. "Females do not want to mate with BPA-exposed male deer mice, and BPA-exposed males perform worse on spatial navigation tasks that assess their ability to find female partners in the wild. This study sets the stage for BPA researchers to examine how BPA might differentially impact the behavioral and cognitive patterns of boys versus girls. Investigators looking for obvious BPA-induced differences, such as chromosome deletions or DNA mutations, could be missing subtle behavioral differences that eventually lead to long-term adverse outcomes, including demasculinization of male behaviors with ensuing decreased reproductive fitness.”

Because BPA is similar to the female hormone estrogen, it may act as an endocrine disrupter affecting the reproductive systems of men and women. The National Toxicology Program (NTP) has concerns about the affects of BPA on brain, behavior and prostate gland in fetuses, infants and children.

“These findings presumably have broad implications to other species, including humans, where there are also innate differences between males and females in cognitive and behavioral patterns,” Rosenfeld said. “n the wide scheme of things, these behavioral deficits could, in the long term, undermine the ability of a species such as the deer mouse to reproduce in the wild. Whether there are comparable health threats to humans remains unclear, but there clearly must be a concern.”

The study will appear in an upcoming issue of Proceedings of the National Academy of Sciences.

This is not the first study linking BPA to adverse health effects. In October 2009, a study published in Fertility and Sterility linked BPA to reduced numbers and decreased quality of sperm in men with detectable levels of BPA in their urine, which may be alarming considering 93% of people over six years of age in the United States have detectable levels of BPA in their urine.

In May 2011, another study presented at a joint meeting of the Pediatric Academic Societies found human children exposed to BPA in the womb had higher incidence of wheezing, a term describing the sound made during a child’s breathing that indicates a respiratory problem. Asthma, airway disorders, inflammation, allergies and infection can cause wheezing.

“[We] have sexually selected traits just like animals do, so there’s no reason to presume that the animals would behave differently than humans,” Rosenfeld told CNN. “It also suggests that the development period is very important — the period when offspring are exposed to endocrine-disrupting compounds. Pregnant women need to start considering what exposure to these compounds is doing to their offspring.”

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