It's another topic receiving catchy headlines. Avid lovers of all things conspiracy theory are, as usual, quick to jump on the bandwagon. This week's bandwagon: Bisphenol A. Sound familiar? BPA, the stuff found in hard plastics and epoxy can liners. I know it's not food, but it finds its way into the body via the pie hole route, thereby making it fair game. So let's discuss: Is this estrogen-mimicking monomer morphing us into menstruating mademoiselles?
BPA is found in polycarbonate plastics, used in the manufacture of medical supplies, phones, CDs and some food/beverage packaging like water bottles. Epoxy resins are used in the lacquer lining of canned foods (to prevent bacterial growth), bottle lids and water pipes. Some dental sealants and composites also contain BPA.
Many articles present BPA as being "toxic". However, pretty much anything can be toxic. The more appropriate question is "do typical doses of BPA present a risk to human health?" Another problem with the reporting of BPA exposure is many articles use the term "low dose". But that's a relative term.
Before BPA gender-bends our proverbial panties in a twist, it's probably pertinent to ponder this question: "are the BPA doses tested in 'low-dose' studies similar to what humans are typically exposed to?"
A new study found that 91-99% of studies claiming to test 'low-dose' exposure to BPA actually tested doses much higher than concentrations corresponding to true peak human exposure. Well, that in and of itself is a problem.
Another problem is many studies draw blood and test urine via plastic medical supplies. See where this is going? Even a BPA-free blood sample will become contaminated with BPA if the plastics used to obtain the sample contain BPA. New studies specifically testing for BPA use BPA-free plastics like polypropylene.
About 90% of BPA is ingested orally. BPA gets its bad wrap as an estrogen mimicking compound - meaning it can bind to estrogen receptors. Estradiol (a steroid hormone) binds 1:1 with estrogen receptors, translation: It binds perfectly. BPA on the other hand has a binding capacity of 1:10,000 meaning that every one in 10,000 BPA molecules are able to bind. Genistein, a soy isoflavone, has a binding capacity of 1:250, much higher than BPA. Genistein is even conveniently sold in supplement form and purported to reduce heart disease, breast and prostate cancer, and post-menopausal ailments.
Still not convinced? BPA is almost entirely inactivated during digestion by your liver; that rather amazing organ, capable of detoxifying things like BPA. A glucose molecule is added to BPA in this process, preventing its ability to bind at estrogen receptor sites. Finally, BPA is excreted in urine or bile 5-7 hours after ingestion. Insert toilet joke here.
A study found that median and 95th percentile values of BPA intake in Americans, 0.1ug/kg/day and 0.4ug/kg/day respectively, were two to three orders of magnitude below health-based guidance values (50ug/kg/day). Again, showing that even those consuming high levels of BPA in the US population are well below the 'tolerable daily intake' of BPA.
In the general population, are levels of BPA sufficient to negatively impact health by way of interfering with estrogen binding? The evidence says no (1, 2, 3, 4, 5, 6).
Take home points:
- BPA is found in many products
- BPA is often found in human urine
- BPA being found in products and urine doesn't equate to BPA being toxic or dangerous for humans - human urine also contains water and electrolytes... just like Gatorade, think on that
- BPA has a very, very weak affinity to bind with estrogen receptors (that is, until it's digested and gets that glucose molecule added and has zero affinity)
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