Exposure to EDCs may negatively affect thyroid function, but more research needed
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Key takeaways:
- Exposure to EDCs may cause thyroid dysfunction, especially among pregnant women and infants.
- More research is needed on the effects of EDCs at different life stages and exposure levels.
SEATTLE — Repeated exposure to endocrine-disrupting chemicals may negatively affect thyroid function, especially for pregnant women and infants, but more research is needed on the synergistic effects, according to a speaker.
During a plenary talk at the AACE Annual Scientific and Clinical Conference, Elizabeth N. Pearce, MD, MSc, professor of medicine in the section of endocrinology, diabetes and nutrition at Boston University School of Medicine and an Endocrine Today Editorial Board Member, gave an overview of how chemicals such as perchlorate and per- and polyfluoroalkyl substances (PFAS) can cause thyroid disruption in humans.
“Thyroid hormone is critically important for brain development in utero and in early life,” Pearce told Healio. “Exposure to environmental thyroidal disruptors in pregnant women and in young children has the potential to decrease IQ and to increase risk for neurobehavioral outcomes such as attention-deficit/hyperactivity disorder. Given the widespread population exposures to potential thyroidal disruptors, this is of significant concern.”
Mixed findings on EDCs and thyroid function
Pearce outlined many ways people can be exposed to endocrine-disrupting chemicals (EDCs). Exposure can occur through food production products, industrial activity that causes pollution, and the use of personal and home care products and medical care products or equipment. Exposure to these chemicals can influence a person’s development across the entire life span, even as early as preconception and gestation. According to a study published in The Lancet Diabetes & Endocrinology in 2016, exposure to EDCs causing hormonal changes contributes to $340 billion in health costs annually in the U.S.
Pearce’s talk focused on two classes of EDCs. One of those chemicals, perchlorate, is used in propellant products, such as rockets, fireworks, matches and air bags. Perchlorate salts are also found in groundwater and can persist for decades in typical groundwater and surface water conditions.
Pearce said perchlorate toxicity may have negative effects on thyroid health, causing reductions in triiodothyronine and thyroxine as well as increases in thyroid-stimulating hormone. These changes could lead to hypothyroidism as well as abnormal fetal and child growth and development. A study using National Health and Nutrition Examination Survey data from 1,135 women with a urinary iodine of less than 100 µg/L found increasing levels of urine perchlorate were associated with decreases in T4 and increases in TSH.
Research analyzing effects of perchlorate levels on thyroid function have been mixed. Pearce said studying the effects of EDCs on thyroid hormones is challenging for several reasons.
“Animal models may not be good predictors of human EDC health effects,” Pearce said. “Effects in humans may be sex-specific or may vary by life stage. Dose-response relationships are not always linear. We are all exposed simultaneously to multiple different disruptors, which may have additive or synergistic effects.”
In a study of 1,880 pregnant women in San Diego County, higher urinary perchlorate levels were associated with lower levels of total and free T4 and higher levels of TSH. In another study conducted among 1,957 mother-infant pairs in San Diego County, perchlorate was not associated with birth outcomes in the full cohort, but for male infants, maternal perchlorate levels were associated with increased birth weight and higher odds for a male preterm birth of 2,500 g or higher.
In a study from Pearce and colleagues, published in The Journal of Clinical Endocrinology & Metabolism in 2010, comparing women with hypothyroidism with those with euthyroid, no correlations were found between urine perchlorate levels and thyroid function. Four years after that paper was published, another study published in The Journal of Clinical Endocrinology & Metabolism that used the same cohort as the 2010 study analyzed whether maternal perchlorate exposure of more than 10.89 g/L was associated with an IQ test score of less than 80 among offspring at age 3 years.
“I was fairly confident we wouldn’t find much and was actually surprised when we saw these results,” Pearce said during a presentation. “We looked at total IQ, verbal IQ and performance IQ in children in association with maternal perchlorate exposure, and what we saw consistently in the unadjusted and the adjusted models was no effect on child performance IQ, but a significantly higher likelihood for having an IQ in the bottom 10% for both total IQ and verbal IQ in children whose mothers had perchlorate exposures in the top 10%.”
Pearce also discussed PFAS, a class of chemicals found in consumer products such as cookware, furniture and carpets, drinking water and seafood. PFAS is also a component of aqueous film-forming foams used for firefighting and training at airports and military bases. Pearce said PFAS exposure could reduce fertility, have adverse developmental effects for children, cause endocrine disruption and increase the risk for obesity.
Research on the effects of PFAS on the thyroid are also mixed. Studies in animal models, in vitro models, the general population and exposed populations have found varying associations between PFAS exposure and its effect on thyroid function.
One study published in 2020 concluded that PFAS exposure negatively impacts thyroid function in pregnant women and neonates. In an analysis of data from the Project Viva cohort in Boston of 726 mothers and 465 neonates, increased PFAS exposure was associated with lower maternal free T4 and lower neonatal T4, particularly among boys.
More research needed
Pearce said a lot more research is needed on EDCs and their effects on thyroid health. She noted that negative thyroid effects of many chemicals may still be unknown. Additionally, research on the effects of chemical mixtures, during different life stages and at different levels of exposure are needed.
“We also need to identify biomarkers which can be used to assess the ability of EDCs to directly interfere with thyroid hormone action without affecting serum thyroid hormone concentrations,” Pearce told Healio.
There are several steps people can take to reduce EDC exposure. People can avoid using pesticides; wash new clothes, kitchen equipment and other products before use; avoid using air fresheners; limit the use of hair dye or nail polish; avoid eating foods wrapped in plastic; replace nonstick pots and pans when they are damaged; and more.
Pearce said even with those actions, people are still exposed to chemicals through other means and emphasized the need for government regulation.
“Ultimately, government regulation will be needed to eliminate or reduce exposures to thyroidal disruptors by ensuring a safe water supply and by phasing out use of particularly harmful disruptors by industry and agriculture,” Pearce told Healio.
References:
- Attina TM, et al. Lancet Diabetes Endocrinol. 2016;doi:10.1016/S2213-8587(16)30275-3.
- Blount BC, et al. Environ Health Perspect. 2006;doi:10.1289/ehp.9466.
- Pearce EN, et al. J Clin Endocrinol Metab. 2010;doi:10.1210/jc.2010-0014.
- Preston EV, et al. Environ Int. 2020;doi:10.1016/j.envint.2020.105728.
- Rubin R, et al. Environ Res. 2017;doi:10.1016/j.envres.2017.05.030.
- Steinmaus C, et al. Environ Health Perspect. 2015;doi:10.1289/ehp.1409614.
- Taylor PN, et al. J Clin Endocrinol Metab. 2014;doi:10.1210/jc.2014-1901.
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Pearce EN. Endocrine disruptors and thyroid health. Presented at: American Association of Clinical Endocrinology Annual Scientific and Clinical Conference; May 4-6, 2023; Seattle.
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