A University of Rochester Medical Center study challenges common assumptions about the chemical bisphenol A (BPA), by showing that in some people, surprisingly high levels remain in the body even after fasting for as long as 24 hours. The finding suggests that BPA exposure may come from non-food sources, or that BPA is not rapidly metabolized, or both.
The journal Environmental Health Perspectives published the research online January 28, 2009.
Controversy around BPA is mounting. In December the U.S. Food and Drug Administration agreed to reconsider the health risks of the chemical, which is used to make plastic baby bottles, water bottles and many other consumer products. Scientific studies suggest that BPA may harm the brain and prostate glands in developing fetuses and infants; adults with higher BPA levels in their urine were linked to higher risks for heart disease and diabetes, according to a study published last September in the Journal of the American Medical Association.
The latest finding from Rochester is important because, until now, scientists believed that BPA was excreted quickly and that people were exposed to BPA primarily through food. Indeed, the FDA and the European Food Safety Authority have declared BPA safe based, in part, on those assumptions.
"Our results simply do not fit that picture," said lead author Richard W. Stahlhut, M.D., M.P.H., of the University of Rochester's Environmental Health Sciences Center. "The research community has clues that could help explain some of these results but to date the importance of the clues have been underestimated. We must chase them much more vigorously now."
Manufacturers use BPA to harden plastics in many types of products. In addition to plastic bottles, BPA is used in PVC water pipes and food storage containers. BPA also coats the inside of metal food cans, and is used in dental sealants.
Stahlhut and colleagues obtained data for a sample of 1,469 American adults through the Center for Disease Control's National Health and Nutrition Examination Survey (NHANES). The researchers sought to explore the link between BPA urine concentration and the length of time a person had been fasting.
Accepting the widely held assumption that food is the most common route of exposure to BPA, Stahlhut expected to see a relationship between the last food ingested, fasting time, and BPA levels. People who had fasted longest (15 to 24 hours), for example, should have had much lower BPA levels than people who had eaten more recently, Stahlhut said.
Instead, those who fasted had levels that were only moderately lower than people who had just eaten. This is significant because scientists expected BPA levels to decrease by about half, every five hours.
"In our data, BPA levels appear to drop about eight times more slowly than expected - so slowly, in fact, that race and sex together have as big an influence on BPA levels as fasting time," Stahlhut said.
According to the authors, two possible explanations may exist for the higher-than-expected levels of BPA in people who fasted. One is that exposure to BPA might come through other means, such as house dust or tap water.
In addition, Stahlhut theorizes that BPA may seep into fat tissues, where it would be released more slowly. However, further study is needed to evaluate the effects of BPA on adipose tissue hormones and function, Stahlhut said, as well as more studies to compare BPA levels in fat versus blood and urine.
The Centers for Disease Control estimates that 93 percent of Americans have detectable levels of BPA in their urine.
The latest data also supports the idea that individuals might be re-exposed throughout the course of a day, Stahlhut said. In 2000 another research group found that BPA can migrate from PVC pipes or hoses into room temperature water, producing another potential route of exposure.
The University of Rochester School of Medicine and Dentistry, and the National Institute of Environmental Health Sciences Training Grant, funded the research.