Exposure to mercury through seafood may be a risk factor for rheumatoid arthritis, Sjögren’s and lupus

Women of childbearing age who are exposed to mercury could be at a higher risk of autoimmune disorders such as lupus, Sjögren’s, rheumatoid arthritis, inflammatory bowel disease and multiple sclerosis, says a study published in Environmental Health Perspectives.
Experts found that mercury – even at low levels generally considered safe – was associated with autoimmunity disorders, which cause the body’s immune system to attack healthy cells by mistake.
“A large number of cases [of autoimmune disorders] 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,” explains Dr Emily Somers, who is involved in the work. “In our study, exposure to mercury stood out as the main risk factor for autoimmunity.”
Researchers looked at data from 1,352 women aged 16–49 years from the National Health and Nutrition Examination Survey. They found that greater exposure to mercury was associated with a higher rate of autoantibodies (an indicator of future autoimmune disease).
“The presence of autoantibodies doesn’t necessarily mean they will lead to an autoimmune disease,” Dr Somers comments. “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.”

Recommendations
“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,” says Dr Somers.
We know, however, that there are many health benefits to seafood. A healthy diet should include at least two portions of fish a week, including one of oily fish, as it is such a good source of many vitamins and minerals, including omega-3 fatty acids. But the NHS advises that there are maximum recommended amounts for oily fish, crab and some types of white fish.

NHS advice

How much oily fish should I eat?
We should eat at least one portion (around 140 grams when cooked) of oily fish a week.
Oily fish can contain low levels of pollutants that can build up in the body. For this reason there are maximum recommendations for the number of portions we should be eating each week. These recommendations are different for different groups of people.

• Women and girls should eat no more than two portions of oily fish a week if they may become pregnant in future or if they are currently pregnant or breastfeeding. This is because pollutants found in oily fish may affect the development of a baby in the womb in the future.
• Men and boys, and women and girls who know they won’t become pregnant in future, can eat up to four portions of oily fish a week.

How much white fish should I eat?
White fish include cod, haddock, plaice, pollack, coley, dover sole, dab, flounder, red mullet and gurnard. You can safely eat as many portions of white fish per week as you like, except for the following, which may contain similar levels of certain pollutants as oily fish:

• Sea bream
• Sea bass
• Turbot
• Halibut
• Rock salmon (also known as dogfish, flake, huss, rigg or rock eel)

Anyone who regularly eats a lot of fish should avoid eating these five fish, and brown meat from crabs, too often.
Even though shark and marlin are white fish, there is separate advice about how much of them you should eat:

• Children, pregnant women and women who are trying to get pregnant should not eat shark or marlin. This is because they contain more mercury than other fish.
• Other adults should have no more than one portion of shark or marlin per week.
Many shark and marlin species are endangered, so we should avoid eating these fish to help stop these species becoming extinct.

How much shellfish should I eat?
Although it is recommended that regular fish-eaters should avoid eating brown crab meat too often, there is no need to limit the amount of white crab meat that you eat. There are no maximum recommended amounts for other types of shellfish.
Eating fish while trying to get pregnant, and during pregnancy and breastfeeding
Eating fish is good for your health and the development of your baby. But pregnant women should avoid some types of fish and limit the amount they eat of some others. This is because of the levels of mercury and pollutants that some fish can contain.
When pregnant, you can reduce your risk of food poisoning by avoiding raw shellfish and making sure that any shellfish you eat is cooked thoroughly.
Below is advice from the Scientific Advisory Committee on Nutrition and the Committee on Toxicity about eating fish when trying to get pregnant, or when pregnant or breastfeeding:

• Shark, swordfish and marlin: do not eat these if you are pregnant or trying to get pregnant. All other adults, including breastfeeding women, should eat no more than one portion per week. This is because these fish can contain more mercury than other types of fish, and this can damage a developing baby’s nervous system.
• Oily fish: if you are trying for a baby, pregnant or breastfeeding, you should have no more than two portions of oily fish a week. A portion is around 140 grams.
• Canned tuna: if you are trying for a baby or are pregnant, you should have no more than four cans of tuna a week. This is because tuna contains higher levels of mercury than other fish. If you are breastfeeding, there is no limit on how much canned tuna you can eat.

These figures are based on a medium size can of tuna with a drained weight of around 140 gram per can. Remember, canned tuna doesn’t count as oily fish, so you can eat this as well as your maximum two portions of oily fish a week.
Due to the higher levels of mercury in tuna, if you’re eating canned tuna, don’t pick fresh tuna as your oily fish.

The National Resources Defense Council has a useful guide to the amount of mercury in fish. Click here for more information.

And click here to read the original research discussed above.

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Image credit: Harold Navarro