Small amounts of mercury in fish and shellfish are unavoidable; traces of contaminants are even found in fish sticks, according to the Environmental Protection Agency, or EPA. On the other hand, tuna is low in saturated fat and rich in omega-3 fatty acids, which can help lower blood pressure, boost your immune system, guard against blood clots and lower triglycerides. Certain types of tuna are higher in mercury than others. The amount of tuna you can safely eat per week depends on the type you choose.
Methylmercury
Methylmercury is simply mercury that finds its way into the ocean as a result of pollution, according to the EPA. Fish and shellfish that live in the ocean absorb methylmercury in varying degrees; some species, particularly older, larger fish have absorbed more methylmercury than others. According to MayoClinic.com, although tuna and other fish and shellfish may contain contaminants, the health benefits they confer are worth the risk of ingesting small amounts of mercury.
Tuna
According to a study by the U.S. Food and Drug Administration's monitoring program, which examined the amount of mercury in fish and shellfish from 1999 to 2010, mean mercury concentration in canned light albacore tuna was 0.350 parts per million, or PPM. Fresh or frozen yellowfin tuna had a mean mercury concentration of 0.354 PPM, and fresh or frozen albacore tuna had a 0.358 PPM. Fresh or frozen big-eye tuna had the most mercury, with a mean concentration of 0.689 PPM.
Recommendations
The FDA recommends you eat up to 12 oz. of fish a week. Select those with the lowest levels of mercury. Canned light tuna is low in mercury, as are shrimp, catfish, pollock and salmon. Restrict your consumption of tuna steak, albacore tuna and chunk white tuna to no more than 6 oz. a week, as these contain more mercury than canned light tuna. The American Heart Association says you can avoid consuming some mercury and other contaminants by removing the skin along with the layer of surface fat on the fish prior to preparing it.
Canned light tuna in water does contain sodium, a mineral that can contribute to high blood pressure when consumed in excess. A 5-oz. can of light tuna packed in water gives you around 360 mg of sodium, or 16 percent of your daily value, or DV. Reduce the amount of salt you get from canned light tuna by choosing "low sodium" or "very low sodium" brands.
Cautions
According to the EPA, your body gets rid of methylmercury on its own, although it can take longer than a year. There are certain types of fish you may want to avoid if mercury concerns you: tilefish, swordfish, shark and king mackerel. The mean mercury levels for these fish are between 0.730 and 1.450 PPM. Pregnant women and those who hope to become pregnant should avoid consuming these types of fish.
References
- U.S. Food and Drug Administration: Mercury Levels in Commercial Fish and Shellfish (1990-2010)
- U.S. Food and Drug Administration: What You Need to Know About Mercury in Fish and Shellfish; March 2004
- American Heart Association: Fish 101; May 2010
- U.S. Environmental Protection Agency: What You Need to Know about Mercury in Fish and Shellfish
- MayoClinic.com: Omega-3 in Fish; December 2010
- MayoClinic.com: Pregnancy and Fish: What's Safe to Eat?; R. Harms, M.D.; February 2011
