Dioxin Exposure Linked to Thyroid Dysfunction

CHICAGO — Exposure to the ubiquitous dioxin chemicals was linked with thyroid dysfunction, a new study found.

Using National Health and Nutritional Examination Survey (NHANES) data, researchers led by Cheng Han, MD, of Boston University and Dalian University in China, identified that exposure to 10 individual dioxins was associated with higher levels of thyroid-stimulating hormone (TSH), which can indicate problems with optimal thyroid function.

And a higher prevalence of hypothyroidism in adults was observed in certain models looking at co-exposure to multiple dioxins, Han reported at a press conference at ENDO 2023, the annual meeting of the Endocrine Society.

The researchers employed three different statistical modeling methods to investigate the combined effects of 20 environmental dioxins on thyroid function, using data from 2,818 participants in NHANES from 2007 to 2010.

High levels of dioxins correlated with higher blood levels of TSH, Han reported. “Although more research on how dioxins affect thyroid function is needed, efforts to reduce exposure to dioxins and other toxic chemicals could help to reduce the risk of thyroid dysfunction and improve public health outcomes.”

Han noted that previous studies looking at the relationship between dioxins and thyroid disease have shown mixed results.

That “might be because other studies looked at specific dioxins, and there are a slew of these chemicals, while this study looked at dioxins as a group,” said Laura Vandenberg, PhD, of the University of Massachusetts Amherst, who was not involved with the study.

“Another reason might be that the mathematical models used were using an assumption that people who have the highest exposure would have the worst outcomes. And actually, that’s often not true for things that interact with the endocrine system,” Vandenberg told MedPage Today. “So these mathematical models that they used in the current study allowed them to find these nonmonotonic effects — which basically means low doses can have effects that you don’t see at high doses. And in endocrinology, we expect to see those.”

Han said it is possible to reduce the risk of dioxins through diet. Dioxins are created by improper incineration of plastics and other industrial products, municipal incineration, forest fire, and even burning of backyard trash. The chemicals fall to earth and become part of the food chain when ingested by wildlife and farm animals. Dioxins usually find a home in the fat cells of animals, and are then secreted in dairy products such as milk and cheese; the substances are also found in highly fat-marbled beef.

Once dioxins are in the body, however, there is not much that can be done to remove them, Han told MedPage Today. “Removing it from the body can be hard. So what we can do is to prevent getting dioxins in the body by being careful what we eat. If we eat less fat tissue, more lean meat, and fruits and vegetables, we will take in less dioxins, so that could be good for us.”

Vandenberg said, however, that while it is difficult to get rid of dioxins in the body, it is not impossible. “If you mobilize the fat by doing things like losing weight, you are also mobilizing these chemicals. But if you do that, you also need to have a high-fiber diet so these mobilized chemicals don’t stay in the bloodstream and cause damage there. But for the most part, once they’re in our bodies, you kind of have to live with how long it takes your body to naturally excrete them, and that can be months or years. In some cases, it can take decades.”

Vandenberg agreed with Han that the best way to keep dioxins out of the body is to eat less fat (which helps on an individual level) and use less plastic, which help society reduce the risk of plastics getting into the air and into the food chain.

Han cited data from the National Institute of Environmental Health Sciences that more than 90% of human exposure to dioxins is through food. The impact of thyroid diseases, such as hyperthyroidism, is associated with increased risk for cardiac complications, hypertension, and heart failure, and hypothyroidism during pregnancy is also associated with adverse neurodevelopmental outcomes in offspring.

Because of the high percentage of dioxins acquired via food, “we should be cautious about testing people for dioxins [since] it is very hard to control dioxin levels,” Han said. Vandenberg noted that most tests for dioxin are performed for academic studies or for government studies such as NHANES, and rarely are performed clinically.