Elizabeth Pearce, MD, MSc, discusses her ENDO 2024 presentation, which found that exposure to some endocrine-disrupting chemicals that harm the thyroid gland has increased over the past 20 years among U.S. women of childbearing age and pregnant women, especially among those with lower social and economic status.
Elizabeth Pearce, MD, MSc, of the Boston University Chobanian & Avedisian School of Medicine recently saw a patient who brought in her own per- and polyfluoroalkyl substances (PFAS) measurements along with thyroid test results, opening up a discussion between doctor and patient about how to avoid exposure to endocrine-disrupting chemicals (EDCs).
“I do not find that patients bring up this topic very often, but I think this will likely change as there is more and more press about EDCs,” Pearce says.
And the Endocrine Society is generating some press on this topic. While exposure to some EDCs that harm the thyroid gland has decreased over the past 20 years among U.S. women of childbearing age and pregnant women, exposure to others has actually increased, and there is particular concern about these exposures among those with lower social and economic status, according to a study presented at ENDO 2024. The researchers focused this study on women who may be particularly vulnerable to negative effects of EDCs on the thyroid: women in their childbearing years and pregnant women.
Pearce, a senior author of the study presented at ENDO, tells Endocrine News that pregnant women are uniquely vulnerable to the effects of thyroidal endocrine disruption because thyroid dysfunction during pregnancy has been linked to adverse obstetric outcomes, and because suboptimal maternal thyroid function in pregnancy may adversely affect fetal brain development. “Therefore, we opted to focus on studying trends in thyroidal EDC exposures in pregnant women and women of reproductive age,” she says.
Here we’ll take a look at how, as the researchers point out, exposure to thyroidal EDCs is ubiquitous and may adversely affect brain development as well as increasing risks for thyroid dysfunction and thyroid cancer. “Exposures to these EDCs have the potential to exacerbate health disparities,” Pearce says.
Two Decades of Data
For this study, Cheng Han, MD, of the Boston University Chobanian & Avedisian School of Medicine analyzed data from the U.S. National Health and Nutrition Survey (NHANES) from 1999 to 2020 for 25,320 reproductive-age women and 2,525 pregnant women. He assessed trends over the past two decades in levels of multiple thyroid-disrupting chemicals in blood and urine samples. Statistical tests helped him to evaluate changes in EDC exposure over time and to identify the effect of socioeconomic status on this exposure.
Han is a visiting scholar from China who spent the last two years with Pearce studying the problem of thyroidal EDCs. Han and Pearce looked at the effects of effects of dioxin exposures on the thyroid gland using the NHANES database, which led to their interest in better understanding changes in exposures to thyroidal EDCs over time.
Han found that exposure to many of the EDCs decreased for both groups of women over the 20-year study period. However, exposure to some thyroid-disrupting chemicals increased. Both reproductive-age women and pregnant women had increased exposure to two types of polyaromatic hydrocarbons over time.
Han says that low-income women who were pregnant or of reproductive age had the greatest increase in exposure to thyroid-disrupting chemicals, especially polyaromatic hydrocarbons. “This increased exposure has the potential to worsen disparities in health outcomes among low-income people,” he says.
“The shifts in exposures to these thyroidal EDCs in pregnant women and women of reproductive age in U.S. were variable, with most decreasing over time but exposure to some (two polyaromatic hydrocarbons and one personal care product chemical) actually increasing,” Pearce says. “Differences by socioeconomic status were variable. However, for most of the thyroidal EDCs, exposures were higher in those with lower socioeconomic status, which has the potential to exacerbate health disparities.”
Naturally Occurring Toxins
Exposure can happen just from stepping out of the front door. Polycyclic aromatic hydrocarbons occur naturally in coal, crude oil, and gasoline. Exposure can occur from breathing air contaminated with motor vehicle exhaust, cigarette smoke, wood smoke, or fumes from asphalt roads. People can also ingest PAH particles in grilled or charred meats or foods.
“Our research underscores the importance of addressing socioeconomic disparities in EDC exposure among women of reproductive age and pregnant women to mitigate potential adverse effects on thyroid health. In addition to counseling patients, endocrinologists have important roles to play as scientists improving our understanding of EDC effects, and as powerful advocates for regulation.” — Elizabeth Pearce, MD, MSc, Boston University Chobanian & Avedisian School of Medicine, Boston, Mass.
And it’s not just from these polycyclic aromatic hydrocarbons: Some EDCs (e.g., pesticides and isoflavones) inhibit thyroid hormone synthesis through inhibition of thyroperoxidase activity, Pearce says. Others (perchlorate, thiocyanate, and PFAS) inhibit the activity of the sodium iodide transporter (NIS), which will impair thyroid hormone synthesis by reducing iodine uptake into the thyroid.
Polychlorinated biphenyls (PCBs), triclosan, bisphenol A, polybrominated diphenyl ethers (PBDEs), and PFAS, have chemical structures with a similarity to thyroid hormone and can bind to and either activate or inactivate thyroid hormone receptors, Pearce continues. Pesticides, dioxins, and PBDEs decrease the half-life of circulating thyroid hormone by enhancing thyroid hormone metabolism in the liver. EDCs may also alter binding of thyroid hormone to circulating binding globulins, interfere with the transport of thyroid hormone into cells, and alter the activity of deiodinases.
“Finally, exposure to some EDCs has been linked to thyroid cancer risk,” Pearce says.
Threat Mitigation
So, what can be done? Avoiding EDCs altogether is impossible, but Pearce says that avoiding the use of plastic containers, bottles, and packaging and consuming fresh and organic food can help. She also points to the Endocrine Society website as an excellent resource for patients because it includes recommendations to thoroughly wash fruits and vegetables before consumption, avoid microwaving plastic food containers, replace older nonstick pans with newer ceramic-coated ones, avoid personal care products containing phthalates and fragrances, minimize handling of receipts printed on thermal paper, and clean floors and remove household dust regularly.
“Optimizing iodine nutrition may also help mitigate the effects of some thyroidal EDCs (particularly those that are inhibitors of NIS),” Pearce says. “It is currently recommended that individuals planning pregnancy or those who are pregnant or breastfeeding should take a daily supplement containing 150 μg of iodine.”
Beyond that, Pearce says that she hopes as awareness grows about the dangers of EDCs, government regulation and consumer backlash may incentivize industry to phase out EDCs in favor of safer alternatives.
EDC Discussions
Pearce – a deputy editor of The Journal of Clinical Endocrinology & Metabolism and member of the Annual Program Steering Committee, and daughter of Catherine Niewoehner Galbraith, MD, an emeritus professor of medicine at the University of Minnesota, credits the Society for the opportunity to meet friends and colleagues. For Pearce, ENDO is annual opportunity not just for great science but for some mother/daughter bonding time. “There is definitely a genetic component to my interest in endocrinology,” she says.
And just as the patient brought in test results to open up a discussion about EDCs, Pearce did the same at ENDO in Boston last June. “Our research underscores the importance of addressing socioeconomic disparities in EDC exposure among women of reproductive age and pregnant women to mitigate potential adverse effects on thyroid health,” she says. “In addition to counseling patients, endocrinologists have important roles to play as scientists improving our understanding of EDC effects, and as powerful advocates for regulation.”
Bagley is the senior editor of Endocrine News. He wrote the December 2024 cover story about Steven Kliewer, PhD, and David Mangelsdorf, PhD, the 2025 recipients of the Endocrine Society’s Edwin B. Astwood Award for Outstanding Research in Basic Science.
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