What influences our behavior more: genes or the environment in which we live? This question has sparked debate for decades. We know both our genetic composition and the environment interact to influence the way we think, feel, and act. But what do we mean exactly by “the environment?” While it is true that the environment can refer to our upbringing, social situations, and other broader contexts, there are also many discrete environmental agents that directly impact our behavior and overall health.

There are several environmental chemicals that disrupt the systems of our bodies. Some examples of these environmental agents include mold, ozone, pesticides, air pollutants, and some foods and medications [1]. Many environment agents are endocrine disruptors. Endocrine disrupting chemicals are chemicals that either mimic or block naturally occurring hormones and disrupt the body’s normal endocrine system functioning. One chemical that is known to disrupt the endocrine system is called Bisphenol A (PBA). BPA is chemical found in polycarbonate plastics, in products including water bottles, baby bottles, compact discs, medical devices, and safety equipment [2].

Looking at BPA’s structure, we see a symmetrical structure with two six-membered ring structures. There is a hydroxyl group (OH) on each of the rings. If we compare the structures of BPA and the sex hormone estrogen, we see that they both have an OH group attached to the six membered ring.

Estrogen is a sex hormone that plays an important role in the growth, development, and functioning of many tissues including the tissues of the male and female reproductive systems, cardiovascular tissues, and bone maintenance [3]. Because of the structural similarities it shares with estrogen, BPA is considered a synthetic estrogen. BPA is able to bind to receptors in our bodies that are intended for estrogen only.  Normally, when estrogen binds to estrogen receptors, the receptor changes its shape or conformation. This conformational change allows for the estrogen receptor to bind with chromatin, which is a complex of proteins and DNA that join together to form our chromosomes. When estrogen binds to chromatin it influences the transcription of specific genes [3].

Based on this knowledge, what will happen if we are exposed to BPA? Well, BPA is going to mimic estrogen. All of the jobs in our body that estrogen does normally will also occur when a synthetic estrogen like BPA is floating around. BPA will bind to estrogen receptors and cause changes in the body, leading to the transcription of genes involved in various estrogenic processes. Given what we know about estrogen, we might expect that BPA exposure would lead to changes in reproductive processes. Sure enough, toxicological studies (studies that assess the effects of chemicals in laboratory animals) show that BPA can lead to tissue changes that lead to mammary and prostate cancers, low sperm count, miscarriage, and chromosomal damage in the eggs of female fetuses [4]. There are also studies in animals that show that BPA plays a role in obesity, insulin resistance, and diabetes. Neurological problems and hyperactivity have also been observed in animals [5,6].

Many of the findings of the toxicological studies conducted in lab animals have been observed in epidemiological studies in humans as well. In women, BPA can lead to ovarian cysts, female reproductive abnormalities, thyroid disruption, and an increased susceptibility to breast cancer. In males, in vitro prostate cancer cell proliferation has been noted, as well as low sperm count. Cardiovascular problems, diabetes, obesity, and liver abnormalities are among some of the other problems associated with BPA exposure.  Lastly, epidemiological studies have shown that prenatal exposure to BPA can lead to a series of behavioral problems, anxiety, and hyperactivity in girls [4]. All in all, BPA, and other synthetic estrogens, can impact our health in a number of ways.

The point of this post is not to freak you out, or make you throw away every plastic product in your house! The purpose of this post is to get us to start thinking about the different components of the environment that can influence our health. Certainly, where you live, where you grow up, the weather, your social context, and things of this nature are all going to impact your overall health and the way you behave. However, it is important to be aware that there chemical agents in the environment that can have a serious impact on our health as well. So, when we say there is a “gene-environment” interaction, we know that chemical agents like BPA found in the environment can quite literally change our genes. Going forward, we should all be mindful of the products we are buying and do our best to limit our exposures to high levels of endocrine disrupting chemicals.

 

References

1. Gene-Environment Interaction (2018). Retrieved from https://www.niehs.nih.gov/health/topics/science/gene-env/index.cfm. (Accessed 3/21/19).
2. Bisphenol A (BPA). Retrieved from https://www.niehs.nih.gov/health/topics/agents/sya-bpa/index.cfm. (Accessed 3/21/19)
3. George G. J. M. Kuiper, Bo Carlsson, Kaj Grandien, Eva Enmark, Johan Häggblad, Stefan Nilsson, Jan-Åke Gustafsson; Comparison of the Ligand Binding Specificity and Transcript Tissue Distribution of Estrogen Receptors α and β, Endocrinology, Volume 138, Issue 3, 1 March 1997, Pages 863–870, doi.org/10.1210/endo.138.3.4979
4. Laura N Vandenberg, Shelley Ehrlich, Scott M Belcher, Nira Ben-Jonathan, Dana C Dolinoy, Eric R Hugo, Patricia A Hunt, Retha R Newbold, Beverly S Rubin, Katerine S Saili, Ana M Soto, Hong-Sheng Wang & Frederick S vom Saal (2013) Low dose effects of bisphenol A, Endocrine Disruptors, 1:1,DOI: 10.4161/endo.26490
5. Y.H. Tian,  J.H. Baek, S.Y. Lee, C.G. Jang. (2010).  Prenatal and postnatal exposure to bisphenol a induces anxiolytic behaviors and cognitive deficits in mice. Synapse, 64, doi.org/10.1002/syn.20746
6. Rachel E. Bowman, Victoria Luine, Samantha Diaz Weinstein, Hameda Khandaker, Sarah DeWolf, Maya Frankfurt. Bisphenol-A exposure during adolescence leads to enduring alterations in cognition and dendritic spine density in adult male and female rats. Hormones and Behavior, Volume (2015)