One of our readers, Caitie, posed an excellent question to The PhDish. Here is her query:
“I have heard a lot about the risks associated with exposure to BPAs. I realize it is nearly impossible to eliminate exposure altogether, but I am curious what kinds of products should be avoided at all costs, which segments of the population are at greatest risk to exposure, what the major consequences of long-term exposure are, etc. Also, while this is not a science-centric question, which major companies are leading the way in reducing BPAs in their products and how can consumers most effectively usher in change from large consumer product corporations (i.e. P&G, Unilever, etc)?”
In this article, I’m going to do my best to address the BPA situation based on what is currently known about it.
First off, what is BPA?
Bisphenol A, or BPA, is a compound found in hard plastic water bottles, soda cans, food cans, receipts, and some household appliances. It is a synthetic estrogen, which means it is similar to – but not quite the same as – the estrogen that normally exists in our bodies.
This similarity to estrogen is the key to why BPA poses a health risk. Let’s try to understand how this works:
Normally, estrogen that is produced by our bodies reaches a specific receptor in our cells, called the estrogen receptor (ER). The binding of the two causes a structural change in the receptor, allowing it to become “activated,” and can in turn activate certain genes. This sets off a multitude of complex signaling pathways, carefully controlled in normal situations.
BPA is a tricky fellow, because it is shaped very similarly to estrogen and can bind to the same receptor just as strongly. But, unlike normal hormones, artificial ones like BPA cause dysregulation of normal signaling pathways, making the hormone systems in our body go haywire. In some circumstances, BPA acts as an anti-estrogen, inhibiting the normal estrogen signaling pathway, while in other conditions the opposite effect is achieved, over-activating downstream genes.
How is this possible? How can one stimulus cause a normal reaction, while another slightly different stimulus cause pandemonium? Although it’s not completely understood, the answer seems to lie in the events that occur right after binding to the receptor takes place. When normal estrogen binds and causes the receptor to change its conformation, it also recruits other molecules called cofactors, which help target ER to its correct functions. BPA also causes a conformational change, but it’s not a perfect fit. This causes different cofactors to arrive at the scene, which lead ER off-track. Depending on how exactly BPA binds to ER in a certain cell, either agonistic or antagonistic downstream effects can occur. The matter gets more complex when you take into consideration two types of ER (alpha and beta), each responding to BPA oppositely. In both cases, however, normal estrogen-ER interactions are overshadowed or even blocked by BPA, leading to problems with hormone signaling. Men, you are not immune to this: BPA is also anti-androgenic, meaning that it interferes with male hormones like testosterone by binding to the androgen receptor and disrupting signaling in much the same way.
Because of this mechanism of action, women who are pregnant are more sensitive to the effects of BPA due to the importance of proper hormone balance for both the mother and the fetus. (BPA has also been shown to accumulate to a greater degree in fetuses compared to adults.) People who already have or are genetically predisposed to diabetes, cardiovascular problems, or hormone-related diseases (such as some breast, prostate, and testicular cancers) are also at higher risk. Being in the United States is also a risk factor: women brought up in the US had much higher systemic levels of BPA than women who had just emigrated from Mexico, speaking to the pervasiveness of BPA in our environment. BPA can enter our system not only by ingestion, but also by absorption through the skin. In normal adults, long-term exposure to BPA can lead to problems with fertility (both men and women), male sex function, miscarriage, neurobehavioral development, cardiovascular disease, obesity, and cancer.
I would now like to address the last part of Caitie’s question, which is an important one: what can we do about this? What products/brands can we safely use?
The answer is a little disheartening. After the pushback against BPA, many companies have stopped using BPA in their products. However, “BPA-free” labels may be hiding a sneaky secret: these products could contain another substance called BPS. Bisphenol S (BPS) doesn’t just sound similar in name to BPA. They are structurally similar as well: below, find the atomic structure of each of these molecules.
As you can see, the only difference between the two compounds is the replacement of 2 methyl groups (carbon and hydrogen, denoted by CH3) with sulphur (S) and oxygen (O). While it is possible for a small change like this to completely alter the properties of a molecule, BPS certainly raises suspicion.
Scientific studies support our suspicions: it appears that BPS does behave similarly to BPA. It is still able to bind the same receptors in our cells, and therefore has very similar effects on us. For example, BPA and BPS are equally capable of reducing the expression of genes in the testosterone synthesis pathway, and lower the amount of testosterone that is secreted by human testes. (In fact, BPS might even be worse than BPA.) The cancer and other long-term data isn’t yet available since BPS is relatively new, but we can reasonably extrapolate that if the basic mechanisms of the two compounds are the same, the long term consequences are likely to be as well.
What about brands that boast BPA and BPS-free products, like Nalgene? Are they safe?
Maybe. But just like they got away with BPS for a while, there may be another harmful chemical modification included in the products. One canned goods company has no BPA or BPS in their can linings, but instead make the linings out of another chemical called titanium dioxide, which has a whole host of other issues. <Read more about it here.> Other companies could be replacing BPA with unknown chemicals – and by the time scientists are able to figure out their long-term effects, decades might pass.
Disposable plastic water bottles (think Aquafina or Poland Spring) fortunately do NOT contain BPA or BPS, and instead contain a chemical called polyethylene terephthalate (PET). So far, the jury is out as to whether PET is dangerous – studies seem to contradict each other on the effects of this substance. One caveat to these studies is that they were only conducted for 10 days, which is a far cry from what a lifetime of exposure could lead to.
Okay, so what can we do? I think the lesson here is that plastic containers have both known and unknown chemical dangers. It is, however, safe to drink water from stainless steel or glass water bottles. This avoids the problem altogether! While we can’t eliminate handling receipts completely, we can try to reduce the amount of time spent holding them or wash our hands soon after. (Note that hand sanitizer does NOT help, and can actually speed up the absorption.)
BPA and BPS are also not the only environmental estrogens out there. Other types are used in things from “microwave safe” plastics to growth stimulants in livestock. By educating ourselves about the reasons behind the risk factors, we can expand our safe practices. For example, we can extrapolate our BPA knowledge and pack lunch in glass Tupperware boxes instead of plastic.
The number of known and potential carcinogens surrounding us can sometimes feel daunting. It’s easy to adopt the “What’s the point of being careful? Something or another will give us cancer anyway” attitude. While the feeling of helplessness is totally understandable, it’s important to not give up. As we become aware of more risk factors, we can reduce or eliminate the ones that are feasible (e.g. replacing our water bottles with stainless steel or glass ones, and using less canned food). If each small action reduces our cancer risk by even one or two percent, several actions can lower our risk significantly.
Stay tuned to The PhDish for more ways to lead a healthy lifestyle! For now, please check out our other articles about cancer, diabetes, and gluten sensitivity.
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