Silent Disruptors: How Environmental Chemicals Threaten Thyroid Health and Development

It is well documented that endocrine-disrupting chemicals (EDCs) are virtually inescapable in everyday life since they are present in everything from food packaging and clothing to flame retardants toys. An upcoming ENDO 2025 session, “Thyroid Disruptors,” examines how EDCs affect thyroid function in pregnancy, childhood, and the link to an increased thyroid cancer risk in populations with a high environmental exposure. 

With evidence proliferating that endocrine-disrupting chemicals (EDCs) affect thyroid hormone synthesis, transport, metabolism, and action; that gestational exposure to environmental thyroid hormone disruptors affects cognitive function; and that exposure in general increases thyroid cancer risk, one session at ENDO 2025 explores these deleterious effects and some of their proposed underlying mechanisms in detail.

“Thyroid Disruptors” happening on Saturday, July 12, features presentations on how thyroidal EDCs affect growth and development in the fetus and in early life as well as on the role of EDCs in thyroid carcinogenesis. As research continues to illuminate the complex relationship between EDCs and thyroid function, the work of these scientists underscores the critical need for a multifaceted approach to this growing public health concern, including coordinated action from researchers, healthcare providers, regulators, and policymakers alike. The “Thyroid Disruptors” session represents an important step toward translating cutting-edge research into clinical practice and public health strategies that may ultimately reduce the burden of thyroid-related disorders and cancers attributable to environmental exposures.

Joris A. J. Osinga, MD, PhD candidate at Erasmus University Medical Center, Rotterdam, The Netherlands is one of the session chairs. His research group at Erasmus MC has extensively studied the effects of EDCs on thyroid function, particularly during pregnancy and in children. “It is well established that many EDCs can alter maternal thyroid hormone levels and even disrupt the thyroid hormone axis,” Osinga says. “Since these chemicals are produced on such a large scale and persist in the environment, their impact goes beyond just individual cases. This makes high-quality, independent research essential to truly understand these associations.”

Osinga received the Eugenia Rosemberg Award at ENDO 2023 in Chicago, an experience he highly values for the chance to have presented his research to an audience of endocrinologists. He was also a 2023 Endocrine Society Early-Career Forum Awardee. He credits membership in the Endocrine Society as having provided him with numerous opportunities to grow both as a researcher and a clinician. “Through the Society, I have been able to engage with leading experts, stay informed about cutting-edge research, and contribute to the broader field of endocrinology. I am very happy to be back at ENDO this year, especially in the role of chairing a session on such an important topic,” Osinga says. “ENDO is the biggest endocrine conference worldwide and a great chance to connect with colleagues and stay updated on the latest research.”

“The developing brain is remarkably malleable as neural circuits are formed. These circuits are strongly dependent on hormones for their development and are extremely vulnerable to disruption. For those reasons, perinatal exposure to EDCs could have lifelong consequences on brain function by altering developmental connectivity.” – Anne Simone Parent, MD, PhD, University of Liege, Liege, Belgium

Although the session outline is still being finalized, Osinga explains that the organizers plan to allow time for an audience Q&A after the presentations. Speaking of the presentations, Osinga says he is familiar with the presenters’ work and has even had the opportunity to connect with some of them personally. “I greatly admire their contributions to understanding the role of EDCs in endocrine function, which is crucial in providing insights that have the potential to inform policymakers and public health strategies,” he says. “I can’t wait to hear the insights from our expert speakers and the discussions that follow.”

Impacts on Neurodevelopment and Cognitive Function

Anne-Simone Parent, MD, PhD, of the University of Liege, in Belgium, will discuss “Effects of Thyroidal EDCs on Growth and Development.” She explains that her clinical work as a pediatrician sparked her interest in this topic, as she has become concerned by the increasing incidence of autism, attention deficits, and learning disabilities. “The developing brain is remarkably malleable as neural circuits are formed,” she explains. “These circuits are strongly dependent on hormones for their development and are extremely vulnerable to disruption. For those reasons, perinatal exposure to EDCs could have lifelong consequences on brain function by altering developmental connectivity.”

As such, Parent’s presentation will focus on the effects of developmental exposure to thyroid disruptors on brain development and cognitive function, drawing on key studies from the literature, such as by Bellanger M., et al. showing that EDCs substantially contribute to neurobehavioral deficits, and Caporale N.O., et al. that identified positive associations between gestational exposure to EDC mixtures and adverse neurodevelopmental outcomes. Collectively, these studies indicate that thyroid function is an important point of vulnerability. “As thyroid hormones regulate key processes such as neuronal proliferation, migration, differentiation, synaptogenesis, and myelination, alterations of thyroid function during critical developmental windows can lead to long-lasting cognitive effects,” Parent says. Additionally, “my laboratory and others have developed preclinical models to study the effects of developmental exposure to EDCs on neural circuits in the hippocampus, a key structure involved learning and memory, and in the cortex.”

Parent explains that some EDCs specifically associated with lower IQ and learning difficulties in children are the industrial pollutants known as polychlorinated biphenyls (PCBs) — now forbidden in the United States and Europe because of their carcinogenic properties and long associated with abnormal thyroid parameters — and flame retardants, which are known to interfere with triiodothyronine (T3) transport, metabolization, and action. Pesticides such as chlorpyrifos are also known to impair thyroid and cognitive function. Perfluoroalkyl substances (PFAS) used, for example, in textiles and cookware interfere with thyroid hormone production and transport. Bisphenol A (nearly ubiquitous among American and European populations) is well known for its weak estrogenic properties, but it has also been associated with decreased thyroid-stimulating hormone (TSH) and thyroxine (T4) levels in pregnancy and in children. 

“In addition to disrupting thyroid function,” Parent says, “many of these contaminants show neurotoxic effects that are probably thyroid hormone independent through direct alteration of key synaptogenic processes. In mice models, gestational and lactational exposure of mice to PBCs disrupted excitatory synaptic function during a period of active synaptogenesis in immature cells in the dentate gyrus, thus providing a window into factors that can disrupt neural circuit formation,” Parent says.

Though banned, PCBs persist in the environment — worse, they harm some populations more than others. Unfortunately, we cannot mitigate these effects solely at the individual level. Parent suggests that: “governments need to ensure the accurate identification of EDCs and screen industrial chemicals prior to their arrival on the market. Scientific knowledge on EDCs needs to be effectively translated to regulatory policies that fully protect populations. Such regulations should be designed to protect the most vulnerable populations: fetuses, children, and pregnant women, but also socioeconomically disadvantaged populations that are known to be exposed to higher levels of environmental pollutants.”

“It is well established that many EDCs can alter maternal thyroid hormone levels and even disrupt the thyroid hormone axis,” Osinga says. “Since these chemicals are produced on such a large scale and persist in the environment, their impact goes beyond just individual cases. This makes high-quality, independent research essential to truly understand these associations.” – Joris A. J. Osinga, MD, PhD candidate, Erasmus University Medical Center, Rotterdam, The Netherlands

Clinicians and researchers can also make a difference. “The National Academies of Science, Engineering, and Medicine, for example, have published clinical guidelines recommending testing and specific clinical follow-up in populations heavily exposed to perfluoroalkyl contaminants (PFAs). This document is a milestone providing a first set of environmental health recommendations for clinicians,” Parent says.

There are several other ways. First, because clinicians know the impact of mild or severe thyroid insufficiency during pregnancy or childhood on brain development, they should be aware of the potential harm of environmental thyroid disrupters in interactions with iodine deficiency. They can also provide patients with recommendations to decrease exposure to endocrine disrupters: “intervention studies have shown that household measures can lead to reduce exposure to EDCs; however, more studies are needed to fully validate exposure-reduction strategies,” Parent says. Clinicians can also support the development of educational materials that enable consumers to identify safer alternatives. Finally, “clinicians should also be aware of the sources of EDCs in healthcare products such as catheters, tubing, parenteral nutrition bags, and disposable gloves and can be involved in researching healthier alternatives,” she adds.

Environmental Exposures and Thyroid Cancer Risk

Maaike van Gerwen, MD, PhD, of the Icahn School of Medicine at Mount Sinai, in New York, N.Y., will present “EDCs in Thyroid Carcinogenesis,” which draws on her team’s 2021 review of the existing literature  as well as their pilot project on PFAS and thyroid cancer. van Gerwen says PFAS will comprise most of her presentation, but that pesticides and other EDCs may make an appearance.

van Gerwen says that she became interested in the topic of EDCs and thyroid cancer after learning about the increase in thyroid cancer incidence among first responders to the 9/11 World Trade Center attack in 2001. Said van Gerwen: “This population was heavily exposed to a dust cloud full of pollutants, including carcinogens,” van Gerwen says. “However, none of the carcinogens had already been linked to thyroid cancer. The dust also included multiple EDCs, so we hypothesized that these chemicals may have led to increased risk of thyroid cancer, an endocrine cancer.”

She explains that her interest grew as patients would ask why they were diagnosed with thyroid cancer, and she was unable to provide a clear answer. “The etiology of thyroid cancer is mostly unknown. So, my work mainly focuses on thyroid cancer, but I am interested in other head and neck cancers as well, mainly because of the exposure route,” she says. “The thyroid is particularly at risk because it is an endocrine organ, and these EDCs are known to disrupt endocrine function.” Overstimulation of the hypothalamic–pituitary–thyroid axis is hypothesized as one of the mechanisms promoting carcinogenesis as well as inflammation and epigenetic changes.

Like Parent, van Gerwen cites the ubiquity and persistence of these substances as challenges to mitigating their harmful effects. “Most of the EDCs that we are particularly interested in (including PFAS) have a very long environmental half-life so they stay in our environment for a very long time. Furthermore, most of the EDCs are still used (e.g., pesticides) so we are exposed to (low) doses on a daily basis. It is very difficult to avoid being exposed,” she says.

“Because there is still a lot unclear about if and how these EDCs lead to negative health effects including thyroid cancer, it is important to start collecting information to better understand certain patterns. It would be a good starting point for clinicians to start asking patients about their profession so that we can better map if certain professions with higher exposure levels (e.g., firefighters, farmers, factory workers) have increased cancer risks and potentially risk of more aggressive cancer. This way, we could better target our cancer screening and management.” – Maaike van Gerwen, MD, PhD, Icahn School of Medicine at Mount Sinai, New York, N.Y.

Her hope for the near future rests with clinicians: “Because there is still a lot unclear about if and how these EDCs lead to negative health effects including thyroid cancer, it is important to start collecting information to better understand certain patterns,” she says. “It would be a good starting point for clinicians to start asking patients about their profession so that we can better map if certain professions with higher exposure levels (e.g., firefighters, farmers, factory workers) have increased cancer risks and potentially risk of more aggressive cancer. This way, we could better target our cancer screening and management.”

Horvath is a freelance writer based in Baltimore, Md. In the March issue, she wrote about the ENDO 2025 session, “Future Developments and Challenges in Obesity Treatment: Where Will We Stand at ENDO 2030?”