Earlier in the year, there was a surge in press coverage of the chemical Bisphenol A (BPA), which is used in the manufacture of polycarbonate plastics and epoxy resins. Since these plastics and epoxies are used in many food containers, the worries focused on the risk of exposure through everything from bottled water to baby food. After reassuring statements from the US Food and Drug Administration and European Food Safety Authority, however, things seemed to quiet down. Expect them to pick up again, thanks to the the publication of a study in The Journal of the American Medical Association that finds high exposure to BPA to be linked with diagnoses of heart disease and diabetes.

The new study relied on data from the National Health and Nutrition Examination Survey. Nearly 1,500 adults, ranging in age from 18 to 74 years old, were surveyed on whether they had obtained diagnoses of various diseases, including different types of heart disease, diabetes, cancer, arthritis, and several others. Urine tests were performed to test the levels of BPA exposure, as the chemical is quickly processed by the liver and excreted. Liver and kidney function tests were also performed by testing for creatinine in the urine and levels of a panel of liver enzymes. Various demographic factors were accounted for, including education, income, smoking, and body-mass index.

There was a strong correlation between body mass index and BPA levels; those within the recommended BMI range carried 3.91ng/mL of BPA, while those in the Obese II category had 6.93ng/mL. There were also correlations with two medical conditions: cardiovascular diseases and diabetes. Those with BPA concentrations a single standard deviation higher than normal faced an odds ratio of 1.39 of having been diagnosed with heart problems, and similar odds of being diabetic.

Viewed another way, those with BPA levels that placed them in the top quarter of the group had nearly triple the probability of having heart disease as those in the lowest. For diabetes, the probability was 2.43. No other disease showed any indication of an association. The authors considered the possibility that BPA was simply a proxy for obesity, with the two being linked because higher food intake increased BPA exposure. The link between BPA and an elevated liver enzyme, however, persisted after obese subjects were excluded.

The authors are rather cautious in their conclusions, noting that the literature on BPA is somewhat confused because different rodents and humans metabolize and excrete the chemical through separate pathways. Still, there is pretty persuasive evidence that BPA can mimic some of the actions of estrogen, and the authors argue that these results merit a prospective study, in which BPA levels are tracked and then correlated with later disease onset, instead of current health issues. The discussion suggests that there is no known mechanism to directly link this activity to cardiac problems.

An accompanying editorial, however, is not so circumspect. In it, the authors argue that responses to BPA and other hormonal mimics often show a biphasic response, in which low levels trigger changes that are distinct from those caused by higher levels, and that this explains the somewhat confusing toxicology. Clear biological responses occur, they argue, at BPA levels well below the current safety standards.

Why hasn't the FDA acted on what the authors term 21st-century biology? "One factor that may be contributing to the refusal of regulatory agencies to take action on BPA in the face of overwhelming evidence of harm from animal studies reported in peer-reviewed publications by academic and government scientists is an aggressive disinformation campaign," they write, "using techniques ('manufactured doubt') first developed by the lead, vinyl, and tobacco industries to challenge the reliability of findings published by independent scientists." This accusation may seem a bit heavy-handed, but I was shocked to discover that BPA has its own website—filled with happy news—sponsored by an industry trade group.

Overall, I tend to favor the more cautious approach suggested by the authors who performed the research. The work needs to be repeated and extended, and there is no clear mechanism that links BPA to cardiac ailments, although the evidence for a link to insulin and diabetes is stronger. Still, it seems imperative that any potential links be explored quickly and thoroughly.

Further reading:

Both articles have been made open access, and contain far more information than can be covered in this news story.