BPA-obesity study virtually meaningless

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In April of this year, the FDA rejected a petition by the Natural Resources Defense Council to ban the use of bisphenol A (BPA) in food packaging. We at ACSH applauded the agency s decision, which was based on a research review finding that normal levels of exposure to this chemical used to protect canned foods from contamination and spoiling do not pose a health risk to humans. So we were more than a little dismayed to see that the latest issue of JAMA features a study linking BPA to obesity in children and teenagers.

For their study, a team led by Dr. Leonardo Trasande of the New York University School of Medicine looked at data from a nationally representative sample of over 2,800 participants, ages six to 19. The children and teenagers had been part of the 2003-2008 National Health and Nutrition Examination Surveys, during which time they had been randomly selected for measurement of urinary BPA concentration. By considering this measurement in light of the participants body mass index (BMI) and controlling for a variety of factors, including ethnicity, age, income, gender, and caloric intake, the researchers found that kids with the highest urinary concentrations of BPA were over two and a half times more likely to be obese.

But hang on. Further analysis showed that the association between BPA urinary concentration and obesity was statistically significant only in white children and teenagers. The researchers admit that this discrepancy is difficult to interpret.

Furthermore, as ACSH s Dr. Josh Bloom points out, there are flaws in both the design and conclusions of this study. First, he says, the measurements were taken at a single time point, which is much less reliable than multiple measurements taken over time. When you re looking at urinary concentration, such a snapshot means very little. For instance, he continues, a higher urinary concentration of BPA could simply mean that you were dehydrated, or that your liver is particularly adept at metabolizing the chemical out of the blood into the urine the way it is typically eliminated.

ACSH s Dr. Elizabeth Whelan is quick to point out that, as many studies have shown, the levels of BPA we re exposed to on a daily basis are extraordinarily low. It seems to me, she says, that the impulse to draw an association between those low levels and obesity is based on the current concern over obesity and the concomitant search for a culprit and a panacea. However, she sums up, the tenuous association noted in this study does not necessarily make for a causal connection.