mercury poisoning
© UnknownLevels of mercury exposure in the United States
Women with high mercury exposures are more than twice as likely to have higher levels of antibodies that are associated with autoimmune disorders.

A large study of women in the United States indicates a link between mercury exposure and elevated levels of a thyroid antibody that is often higher in women with autoimmune diseases, such as arthritis and lupus.

The findings may be the first evidence that mercury exposure in U.S. women affects the immune system through the thyroid. Whether these changes in the immune system lead to thyroid or general health problems is not known.

The results are in line with previous human studies that show links between mercury and autoimmune disease. Other studies with job related - as well as dietary - mercury exposures find associations with changes to immune system antibodies, as this new study does.

Mercury is found in all organisms - plants, animals, bacteria and humans. Most exposures in people occur primarily from eating fish, which contain the organic form known as methylmercury. For this reason, fish consumption advisories are common in certain regions of the United States and the world.

In sufficient doses, methylmercury can affect the developing nervous system in the developing fetus and in growing children. In adults, elevated methylmercury exposure can lead to neurological problems, such as memory loss and tremors. Recent studies show that methylmercury exposures can also lead to cardiovascular and immune effects.

Yet, little is known about how the immune system responds to mercury in any form.

To find out more, scientists analyzed data collected from 2,047 women between 2007 and 2008 during a large study in the United States, the National Health and Nutrition Examination Survey (NHANES). They compared total mercury levels in blood and autoantibodies - immune system factors that fight the body's own cells and indicate autoimmune disease.

They looked at two autoantibodies - thyroglobulin autoantibody and thyroid peroxidase autoantibody - that attack proteins made by the thyroid gland. Patients with autoimmune diseases, such as lupus, rheumatoid arthritis and fibromyalgia, often have elevated concentrations of these antibodies. The scientists limited their study to adult women, because women are more likely to have autoimmune disorders.

They found that women with the highest blood mercury levels were more than twice as likely to have elevated levels of thyroglobulin antibody compared to women with the lowest mercury levels. However, they found no relationship between mercury and the thyroid peroxidase antibody. The highest mercury blood concentrations included levels considered safe for most people - less than 5 micrograms of mercury per liter of blood (µg/L) - and levels generally lower than mercury exposure reported in similar studies.

Overall, the study provides new evidence for the emerging role of mercury in autoimmune disease. Additional studies should tease out the effects of different chemical forms of mercury.

Gallagher, CM and JR Meliker. 2012. Mercury and thyroid autoantibodies in U.S. women, NHANES 2007 - 2008. Environment International