Researchers, clinicians, environmental groups and the media have all sounded the alarm on BPA, pointing to a large body of animal evidence which suggests that it has estrogenic effects (i.e. increases estrogen activity) which in turn cause numerous health problems, ranging from obesity to infertility.
But recent evidence in humans (and animals) has led me to reconsider my original position on BPA. In a commentary published in the journal Toxicological Sciences, Dr. Richard M. Sharpe, a leading global expert on male reproductive health, reviews several studies which suggest that BPA is an extremely weak estrogen at levels of exposure that humans are likely to experience in the real world. (1) In fact, even at levels 4,000 times higher than the maximum exposure of humans in the general population, there are “no discernible adverse effects”. (2) Studies conducted by other groups on oral exposure to BPA at doses obtained in everyday life have also failed to find any negative effects on reproductive health or sexual development. (3) Sharpe explains that much of the early research indicating harm from BPA was flawed because it used far larger doses than humans could ever reasonably be exposed to, or methods of delivery (i.e. injections or implants) that don’t reflect real-world routes of exposure.
The history of science is the history of scientists being wrong most of the time
These findings may come as a surprise to you. They may even shake your faith in science. After all, if scientists were so wrong about BPA, what else are they wrong about? Plenty—as I’m sure you already know. (Cholesterol and heart disease? Salt and high blood pressure? Giving estrogen to post-menopausal women to prevent heart disease? The list goes on and on.) It wouldn’t be a stretch to say that the history of science is the history of scientists being wrong about most things most of the time. If you doubt this, just look back even 100 years at prevailing opinions in science and medicine. Unfortunately, we often forget that people living 100 years from now will look back at our closely held beliefs with the same mixture of amusement and scorn. Dr. Sharpe alludes to this in his commentary:
Anyone involved in biomedical research knows that scientific ‘‘facts’’ that remain untouched by the ravages of further research are a rare commodity. Usually, most facts change their form with time (evolve), and their meaning, and probably their importance, also will change. Disappointing as this may be for our scientific egos, it represents something far more important—scientific progress. It is inevitable that scientific progress, in the form of new facts, will trample over our bright ideas, hypotheses, and even over our results. This apparently destructive process is in fact constructive, and as scientists, we have to embrace this evolution and to accept that the sacrifice of our initial beliefs (and our precious results and our interpretations) is part and parcel of advancing understanding.
That’s one of the most refreshing and honest passages I’ve ever encountered in a scientific paper.
Another issue is that policy makers, clinicians, the media, (and I would argue) the general public want certainty and black and white answers. Yet the process of scientific inquiry is inherently full of uncertainty and “gray areas”. Again from Dr. Sharpe—this time from an interview in Forbes Magazine (4):
There’s still the camp who is ignoring a lot of the evidence, and which remains the most vociferous. One of the issues is that in science nothing is ever absolutely black or white; but if you ignore a lot of the evidence – the bits that don’t fit – you can make something black and white…
…What is never stressed enough is that scientists work at “the borders of ignorance” – what is in front of us is unknown and we try to find our way forward by making hypotheses based on what is known. This means that we are wrong most of the time, and because of this scientists have to be very cautious about interpretations that are based on our projected ideas about what is on front of us. What decision-makers, politicians and the public want is unequivocal guidance, not uncertainty. So this creates a dilemma for scientists. Those who are more prepared to throw caution to the winds and make unequivocal statements are more likely to be heard, whereas a more cautious scientist saying “we’re not sure” will not be taken notice of. The bisphenol A saga has until recently been a story of such contrasts.
The messy intersection between science and humanity
Sharpe’s comments highlight the messy intersection between science and humanity. Most of us don’t tolerate uncertainty very well. We want clearly defined, unequivocal answers that we can act on. I suspect this is an evolutionary mechanism: if we’re exposed to a threat in a natural environment, indecision or uncertainty could threaten our survival. Unfortunately, this (innate?) desire for certainty works against us in the realm of scientific inquiry, which instead invites us to live in a world of gray where “right” and “wrong” are moving targets and relative terms. As Dr. Sharpe said above, scientific progress requires us to continually challenge our beliefs and revise our hypotheses when they are no longer supported by the evidence.
Does this mean we should disregard all scientific research? This is perhaps a natural response, but I don’t think it’s the right one. It is possible—though not always easy— to separate good evidence from bad. For example, one of the golden rules of scientific research is that an original result be repeatable by large studies conducted in a rigorous manner by researchers at other laboratories. Bisphenol A failed this test, as studies following the initial negative findings did not support the conclusion that BPA is estrogenic. Yet there are many other findings we can be more confident of, because the quality of evidence supporting them is higher.
Speaking personally, this is yet another reminder that humility and a spirit of curiosity and non-attachment are perhaps the most important qualities I can cultivate as a research-oriented clinician. I have been wrong before and I most certainly will be wrong again. I can’t guarantee that everything I write here is correct, and won’t be disproven or at least altered in some way at a future date. But the commitment I can make to you is that I will continue to challenge my assumptions and beliefs, and admit when I am wrong. That’s the best I can do—and I believe it’s the best anyone working in science or medicine can promise.
Why avoiding BPA still might be prudent
Though I’m impressed with Dr. Sharpe’s critique of the research suggesting that BPA has estrogenic activity, I’m not yet ready to proclaim that BPA is harmless. There are two reasons for this. First, as you can imagine, Sharpe’s critique—and others like it— have been challenged by many of the scientists who’ve published work suggesting BPA has estrogenic activity. In a six-page letter to the editor in Toxicological Sciences, Dr. Fredrick vom Saal, who published the seminal 1997 study indicating that low doses of BPA have estrogenic effects, defended his hypothesis. (5) He argued that his team’s initial results have, in fact, been replicated by many other groups around the world, and as of March 2005 there were 104 publications reporting in vivo estrogenic activity of BPA in animals and humans at doses lower than the current reference dose in the USA of 50 µg/kg/day. He also points out that some prominent critics of the BPA-estrogen connection have longstanding ties with chemical corporations, which casts suspicion on their motives.
Second, there’s a large body of research suggesting that BPA may have other harmful effects above and beyond its estrogenic activity. For example:
- A 2008 review found an association between higher BPA exposure and cardiovascular disease, diabetes and elevated liver enzymes. (6)
- A study published in 2012 found that maternal exposure to BPA decreases thyroid hormone levels in male (but not female) babies at birth. (7)
- A 2013 study demonstrated an association between postnatal urinary concentrations of BPA and asthma in children. (8)
- Another 2013 study found a relationship between urinary BPA concentrations and childhood behavioral and learning development. (9)
These studies are observational, so the standard caveats apply. (And we’re not going to see randomized clinical trials evaluating BPA’s harmful effects because such research wouldn’t be ethical.) So we’ll have to just live with the uncertainty until the data become more clear.
In the meantime, I prefer to avoid plastic as much as possible because I see little downside to doing so. I dislike using plastic water bottles and containers for several reasons (possible health consequences, environmental impacts, taste, etc.), and my family has already made the shift to using stainless steel and glass instead of plastic for storing and transporting food and beverages. I don’t think I’ll ever look back and say, “Gee, I sure wish I would have used more plastic containers,” but I can certainly see myself regretting NOT eliminating them if it turns out that BPA and other plastics do have harmful effects. (For recommendations on how to reduce plastic use, see my previous article on plastic food containers.)
I’d like to close with one last quote from Dr. Sharpe (from his commentary in Toxicological Sciences):
If this short opinion piece does nothing else, I hope that it will remind us all of the central importance to be attached to the repeatability of experiments and how we should react when a study proves to be unrepeatable. As scientists, we all like our ideas and hypotheses to be proved correct; yet, there is equal merit in being proved wrong. The ideal hypothesis is one that can be shot at, and in most cases, it ends up full of holes (at best). This is the tried and trusted way via which scientific understanding moves onward, and ultimately, our own convictions and presumptions cannot stand in its way.
Now I’d like to hear from you? How did this post affect you? Does it make you less likely to trust scientific studies? Have you taken steps to reduce your exposure to BPA—and will you continue to do so?
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