Mouse Study Contradicts BPA Link to Obesity

ANN ARBOR, Mich.A new study published in the Journal of the Federation of American Societies for Experimental Biology contradicts the notion that maternal exposure to the chemical bisphenol A (BPA), commonly found in food and beverage packaging, may be a factor in obesity.

Researchers at the University of Michigan School of Public Health found female mice exposed to BPA through their mother's diet during gestation and lactation actually were found to be hyperactive, exhibit spontaneous activity and had leaner body mass than those not exposed to the chemical.

For the study, the researchers exposed mothers to three different levels of BPA in the diet then followed the offspring through adulthood at three, six and nine months of age. The average lifespan of a mouse is two years, so by three months they are young adults. As to why only females exhibited the excessive activity and lean bodies, the researchers said it bears more study, but because BPA is known to impact estrogen and thyroid hormone, most likely it is affecting these natural hormones in the females.

"We looked at several different metabolic phenotypes, including spontaneous activity, food intake, energy expenditure and body composition. I think the most striking result we saw was the increased activity in these animals," said Olivia Anderson, doctoral student in environmental health sciences and lead author on the paper.

The researchers said their hypothesis going into the study was that BPA would act as an obesogenic agent. While there is some preliminary evidence that it does, there are differences in exposure, duration and when you actually measure the individual.

Recent evidence in humans only looks at one time point. What we're really interested in is BPA exposure during early development, and how that affects health throughout life. So those are two very different questions," said Dana Dolinoy, the John G. Searle Assistant Professor of Environmental Health Sciences and senior/corresponding author of the study. "There are several things we need to look at in evaluating studies investigating BPA as an obesogen, such as composition of the diet. Not all these diets are similar throughout these studies. Some may have high-fat diets. Some may have diets with different protein levels. Then there is the difference in exposure timing and doses of exposure of BPA. It's important to dig a little deeper and actually look at the mechanism that BPA is acting upon."

In December, the researchers released a study that found BPA in human fetal liver tissue, demonstrating that there is considerable exposure to the chemical during pregnancy. That research also found that the BPA in fetuses was in a form not eliminated from the body, unlike previous studies that showed adult humans metabolize and rid their bodies of the chemical.