Science News gets it right on bisphenol A
Writing in Science News, reporter Rachel Ehrenberg describes a new result just online in Environmental Health Perspectives that uses human data to link bisphenol A to heart attacks and type 2 diabetes. Scientists from the University of Cincinnati have discovered that BPA, at levels comparable to that found commonly in human serum, suppresses release of a hormone (adiponectin) from fat tissues that normally helps protect people from these major diseases. The results predict that greater BPA levels will be associated with higher risk to heart attacks and type 2 diabetes.
In a nice touch, Ehrenberg interviews a Spanish scientist, Angel Nadal, who has been one of the pioneers in exploring how BPA affects insulin metabolism, using lab experiments with mice. It's unusual to see a US-based reporter going to the trouble of locating and interviewing European scientists on these issues, even someone as distinguished as Nadal. Nadal's quotes address both the science and the politics of BPA: "I do not understand why the governments of the United States and Europe put money into studying pollutants like bisphenol A and then later don’t listen to what scientists have found,” comments Angel Nadal, of the Spanish Biomedical Research Network in Diabetes and Associated Metabolic Disorders in Alicante, Spain. “They are using a last century approach to toxicology.”
One point Ehrenberg might have explored further: With her article, Science News includes a dramatic graph taken from the new scientific paper showing that the strongest effect observed occurred at a BPA concentration of 1 nanomolar (approximately 1 part per billion). By the time that the concentration rises to 100 nM, the effect disappears. The graph shows that BPA's effect is also apparent at 0.1 nM. This is a clear example of a non-monotonic dose-response curve (NMDRC). Dose-response curves like this are common in studies by endocrinologists of hormones... they're often called 'biphasic.' But they are regared as an anathema, if not an illusion, by traditional toxicologists. As endocrinologists have become involved in the study of hormone-like contaminants (endocrine disruptors), they are discovering that these NMRDCs are commonplace... and exactly what endocrinologists would expect. But they violate basic assumptions of regulatory toxicology. Indeed, all safety testing conducted by the FDA, the EPA, etc., assume that they don't occur. That's what Nadal is referring to above about a 'last century approach to toxicology.' And it's one of the key reasons why the FDA is having trouble getting the science right on health risks of BPA.
For a detailed discussion of the new paper, by Hugo et al., try here.