Although structural similarity is subjective, receptor-binding affinity is not. Estradiol, the most important of the estrogens, binds about 12,000 times more tightly to estrogen receptors than to BPA. Thus, if BPA is an endocrine disruptor, it is a mighty poor one. This is the primary reason BPA scares are unfounded.
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But there is another.
As the name implies, BPA is a member of a class of organic compounds called phenols—molecules that have a hydroxyl group attached to a benzene ring. Phenols are known to be notoriously difficult to work with for medicinal chemists, given they are tasked with discovering new drugs. Although an experimental phenol-containing drug may work very well in a “test tube,” the story in a living animal or human is quite different.
The reason phenols are poor candidates is the same reason BPA does not remain in our bodies. Phenols are known to rapidly undergo a particular type of metabolism called conjugation, in which the hydroxyl group is coupled to one of a small number of ubiquitous, highly water-soluble biomolecules. The resulting conjugate then becomes water-soluble and is excreted in the urine.
Conjugation is a very important mechanism for eliminating multiple chemicals, either natural or synthetic, that are exposed to our bodies. This is why when BPA is measured in studies it’s almost always sampled from urine.
As is the case with many other phenols, BPA is rapidly conjugated and eliminated; it does not accumulate in our bodies. That it’s found in urine simply means our livers are doing exactly what they are supposed to do. If it were not found in urine, it’s conceivable it could accumulate in the body and do harm.
It is more than a little ironic that the so-called “BPA Scare Industry” is making troubling claims, when, in fact, detection of BPA in urine is an indicator it is not doing harm.
The FDA has spoken. Science has spoken. Enough.
Dr. Bloom is the director of chemical and pharmaceutical sciences at the American Council on Science and Health. Reach him at firstname.lastname@example.org.
This column is being published with the permission of the American Council on Science and Health.