Exposure to mercury is linked to a higher likelihood of developing autoimmune thyroid disease, and cadmium exposure interferes with the production of thyroid hormones.

This study found that when moms are exposed to mercury during pregnancy, their babies have higher levels of a hormone (TSH) that means the thyroid isn’t working right. Cadmium was also linked to thyroid problems, though not directly shown to block hormone production.

This study found mercury in the thyroid glands of many older people and says it might cause immune problems in the thyroid, which supports part of the claim. But it didn't prove that cadmium stops the thyroid from making hormones.