How Fish Might Affect Your Immune Health

Mercury in fish and seafood may raise risk of autoimmune disease in women

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) Seafood is always a great choice for protein if you’re young and female, right? Not so fast.

A new study found that the mercury in seafood might increase the risk of autoimmune problems later in life. Autoimmune diseases include rheumatoid arthritis (RA), pernicious anemia, multiple sclerosis (MS), celiac disease and type 1 diabetes.

However, the authors of this study stressed that it's too early to say for certain that mercury causes autoimmune problems.

Normally, the immune system protects patients from infections. Occasionally, however, the body begins to attack its own cells as if they were invaders.

Depending on the condition, patients might have the aches and pains of arthritis. Or they could have the low red blood cell count of anemia or the aches, pains, and weakness of RA and MS.

If you have celiac disease, you can’t eat wheat. If you have type 1 diabetes, your body stops producing insulin, the hormone that regulates your blood sugar.

Although science has much to offer in terms of treating these diseases, the question is this: why do they start? And women may be particularly susceptible to autoimmune problems.

Enter lead study author Emily C. Somers, PhD, ScM, an associate professor at the University of Michigan Medical and Public Health schools in Ann Arbor. Dr. Somers and her team wanted to know whether mercury exposure could increase the risk of autoimmune disease in women.

"We don't have a very good sense of why people develop autoimmune disorders," Dr. Somers said in a press release. "A large number of cases are not explained by genetics, so we believe studying environmental factors will help us understand why autoimmunity happens and how we may be able to intervene to improve health outcomes. In our study, exposure to mercury stood out as the main risk factor for autoimmunity."

These researchers studied data from an existing study called the National Health and Nutrition Examination Survey (NHANES). This large survey collected data over several years that included what people ate.

Dr. Somers and team looked at more than 1,300 women aged 16 to 49.

They used lab test results from hair, blood and urine to determine whether the women had been exposed to mercury. They also collected data regarding what the women ate.

Finally, they looked at antinuclear antibodies (ANAs) in the women’s’ blood. A positive ANA test indicates a woman is more likely to develop autoimmune disease.

Dr. Somers and colleagues found that women who had higher blood and hair levels of methylmercury were more likely to have increased ANA levels. Methylmercury is found in dental fillings and in some fish and seafood.

These researchers noted that women of childbearing age should be mindful of their fish intake. Doctors often encourage women who are or may become pregnant and nursing mothers to eat seafood because it is a good source of protein and other nutrients.

A pregnant woman can safely eat up to 12 ounces of seafood a week, according to expert sources like the US Food and Drug Administration and the Environmental Protection Agency. Swordfish, king mackerel and tilefish typically have the highest levels of mercury. Shrimp, canned light tuna and salmon usually have lower mercury levels.

Dr. Somers and team stressed that the association between mercury and autoimmune disease is tenuous.

"The presence of autoantibodies doesn't necessarily mean they will lead to an autoimmune disease," Dr. Somers said. "However, we know that autoantibodies are significant predictors of future autoimmune disease, and may predate the symptoms and diagnosis of an autoimmune disease by years. For women of childbearing age, who are at particular risk of developing this type of disease, it may be especially important to keep track of seafood consumption."

This study was published Feb. 10 in the journal Environmental Health Perspectives.

The National Institutes of Health (NIH), the National Institute of Environmental Health Sciences and the NIH National Center for Research Resources funded this research. Dr. Somers and team disclosed no conflicts of interest.

Review Date: 
February 11, 2015
Last Updated:
February 14, 2015