Not so long ago a colleague and I wrote on The Huffington Post about the potential health dangers of the thousands of "endocrine-disrupting" chemicals that are pervasive in our environment. Our hope was that we could nudge, in some small way, the forthcoming decision from the FDA on whether to ban BPAs in food and beverage containers.
Unfortunately the FDA didn't see the research in the same way we did. They chose to ignore what seems plain to us, that these chemicals are transforming our bodies and minds, and that we should err on the side of caution in exposing ourselves to them. As we wrote:
There is a long scientific history showing a link between exposure to endocrine disruptors and reproductive disorders such as infertility and early puberty. Furthermore, the evidence is growing that the damage is much more widespread. In studies of animals, both in the lab and in the wild, these chemicals have been shown to increase the risk of various cancers, to contribute to obesity, and to influence the activity of neurotransmitters in the brain. In fact, there are even hints that exposure to the chemicals may have something to do with the dramatic rise in autism and mental disorders over the past few decades.
This week another colleague and I published the results of a study that shows, for the first time, how an individual's ancestor's in utero chemical exposure, coupled with stress in that individual's own life -- generations later -- can combine to alter behavior even more dramatically than either kind of exposure does on its own. The paper appears in this week's issue of the Proceedings of the National Academy of Science.
It is a model, in other words, of how this is likely to be working in the real world, where it's not one exposure to one chemical that's likely to be determinative of a disease or a condition or a behavioral tendency. Life rather is a complex series of exposures -- to different chemicals, better or worse nutrition, varying degrees of stress, etc. -- that cumulatively change the patterns in how our genes are expressed. And those "epigenetic" changes alter our predispositions to different health and behavioral outcomes.
Our experiment was a proof of principle study. We subjected rats to a "two-hit" scenario. There was an in utero exposure to vinclozolin, which is a common fungicide used on fruits and vegetables. Then we let the rats reproduce and looked at how their great-grandchildren responded to stress during adolescence -- the second hit -- when they became adults. This was in comparison to a control group of rats whose ancestors weren't exposed to the fungicide or to the stress.
What we found was striking. Even before they were stressed, vinclozolin-imprinted and control mice performed significantly differently on a number of standard tests that measure anxiety, emotionality, and social responsiveness (they were also overweight, though that's a story for another time). But if they were also stressed as adolescents, those differences were in some cases exacerbated later in adulthood.
On one test, for instance, the stressed-out, vinclozolin-imprinted males were significantly more interested in spending their time with other rats than their control counterparts, who were more willing to split their time between socializing and exploring. It was as if, after the double whammy of ancestral exposure and the stress in their own adolescence, the affected males became more needy.
It's not difficult, nor is it inappropriate, to make the connection between results like these and one of the big questions that's been haunting our society for the past few decades: Why are so many mental health disorders on the rise?
We haven't proved that chemical exposure is at the root of increases in autism, bipolar disorder, anxiety and depression, and similar conditions. My guess is that we'll eventually discover a significant connection with at least some of these conditions, but we don't know yet.
What we do know with increasing confidence, however, is that chemical exposure is changing our brains, and that those changes are being passed on to our descendants. Not all of those changes are likely to be beneficial.
Maybe next time around, the FDA will take note.
This post has been updated since its original publication.