BPA Makes Male Mice Less Masculine and Less Appealing to Mates

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Mice that were exposed in the womb to bisphenol A (BPA), a chemical found in many plastic products and the linings of food and beverage cans, grew up to be less masculine and less attractive to females, a new study finds. The results may not be translatable directly to boys, but the authors suggest they may shed light on certain subtle effects of BPA.

In their new study, researchers from the University of Missouri-Columbia fed one group of pregnant deer mice with BPA-tainted food and another with uncontaminated food. When the pups were born, the researchers conducted a series of experiments on the male offspring as they matured.

“The BPA-exposed deer mice in our study look normal; there is nothing obviously wrong with them. Yet, they are clearly different,” said lead author Cheryl Rosenfeld, associate professor in biomedical sciences at Missouri’s College of Veterinary Medicine, in a statement.

In one experiment, the mice were sent into a maze. The mice that had been exposed to BPA in the womb were less able to find their way through the maze and were also less interested in exploring. The authors described these behaviors as evidence of demasculinization, since navigational skills and an interest in exploring are key traits among male deer mice — essential for helping them find potential mates in the wild.

In another experiment, fertile female deer mice were released into an enclosure with two male mice: one that had been exposed to BPA and one that did not. Researchers observed that the females were twice as likely to express sexual interest in the BPA-free male as in the exposed mouse. (How does a mouse express sexual interest, you ask? Nose-to-nose contact, apparently.)

Of course, it’s too soon to say whether the findings may apply to humans, but what’s notable about the new study is that researchers did not find differences in hormone levels in the exposed and unexposed mice. Health.com’s Ella Quittner reported:

For instance, the levels of testosterone and another hormone in adult BPA-exposed mice were no different from those in the unexposed mice, which suggests that BPA exposure affects the behavior of male mice without altering their adult hormone levels.

It also suggests that researchers may need to look beyond adult hormone levels when designing BPA studies in humans, says John Meeker, Sc.D., an assistant professor of environmental health sciences at the University of Michigan School of Public Health, in Ann Arbor.

To date, studies of the effect of BPA in humans have been inconclusive. One study of high BPA exposure in Chinese factory workers found that it was associated with sexual dysfunction. Other data have linked that the chemical with a variety of other ills including diabetes, asthma and obesity. A small 2009 study looking at exposure to pthalates — another type of endocrine-disrupting chemical in plastics — found that boys who were exposed in the womb showed “less masculine” play behavior at about age 4 to 6.

Many manufacturers in the U.S. have eliminated BPA from their products, largely due to public concerns. In 2010, the Food and Drug Administration also issued a statement of concern about the potential harms of BPA to fetuses and small children. But unlike the Canadian government, which has banned BPA in baby and kids products and officially declared it a toxic substance, the U.S. has not followed suit.

The study was published online by the journal Proceedings of the National Academy of Sciences.