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Tuesday, January 15, 2013

A negative study on Bisphenol A



In science, it's critical to repeat experiments. Unless you can replicate results, you can't be sure that you're seeing a true effect. A new agouti mouse study about the effects of Bisphenol A is a prime example of why this is so. 

Agouti mice can produce offspring with colors varying from black through brown to yellow. These differences are not genetic, the baby mice can look completely different despite being genetically identical. Rather, the coat color differences are caused by epigenetic changes. There are two interesting things about this. First, the environment of the pregnant mother (what she eats or is exposed to) affects the coat color of her young, and second, the yellowest pups are the sickest, exhibiting ‘metabolic syndrome’ (obesity and diabetes) as they age. I think you can see where this is going. Researchers can expose the mommy mice to different conditions and directly observe how these conditions will affect the future health of the babies.

Among the environmental conditions of current interest is exposure to Bisphenol A (BPA). BPA is an endocrine disrupter. It mimics estradiol by binding to estrogen receptors and has been implicated in a variety of health issues. Prior studies with agouti mice have shown that giving mother mice BPA causes more of her offspring to have yellow coats. In other words, the maternal exposure was predisposing the fetuses to later illness. 

University of Missouri researchers, led by Cheryl Rosenfeld, repeated these experiments with three different concentrations of BPA and found that the chemical had no effect. Let me repeat that. In this new study, maternal exposure to BPA did not set off the baby mouse color-coded biohazard alarm.

To be clear, this study does not prove that BPA is safe for people and certainly not that it’s safe for pregnant women to consume. There are many studies showing that BPA is in fact harmful. This new data does, however, demonstrate the necessity for repeating experiments, particularly when health claims are being made. It also shows that we do not yet understand everything about BPA.

Rosenfeld CS, Sieli PT, Warzak DA, Ellersieck MR, Pennington KA, & Roberts RM (2012). Maternal exposure to bisphenol A and genistein has minimal effect on Avy/a offspring coat color but favors birth of agouti over nonagouti mice. Proceedings of the National Academy of Sciences of the United States of America PMID: 23267115.