Mercury is a toxic metal with significant effects on the thyroid. There is ample evidence that mercury leaches from dental amalgam fillings and contributes to thyroid disease and anemia.
While large doses of mercury can induce hyperthyroidism, smaller amounts can induce hypothyroidism by interfering with both the production of thyroxin (T4) and the conversion of T4 to T3.
Mercury disturbs the metabolism of copper and zinc which are two minerals critical to thyroid function. Gray hair can be an indication of mercury accumulation, more so in females than males.
Mercury causes disruptions to the immune system functioning and promotes the production of IgG and IgE autoantibodies which also are involved in autoimmune thyroid disease.
Different forms of mercury, organic or inorganic, have different effects on the thyroid. Milk and quite likely estrogen cause an increase in the absorption of mercury.
Mercury has a very long half-life in the body with a duration of perhaps many years and has been found in cancerous tissues.
Selenium is the key mineral which protects the body from mercury toxicity. One study showed that cilantro (Chinese parsley) helps remove mercury from the body and protects the body from pre-cancerous lesions.