Consumption of tuna, the most commonly eaten fish in the United States, accounts for one-third of mercury exposure from eating seafood, a new study shows.
The study is in this month's issue of the journal Environmental Research, and shows that mercury content varies widely depending on the variety of fish. In all, 51 varieties of seafood are ranked based on mercury content.
Salmon, catfish and flounder have low levels while bluefin tuna and swordfish are among the varieties that have the highest levels. Shellfish and crustaceans such as clams and crabs were listed with low mercury levels, according to the study.
But the National Fisheries Institute's registered dietitian Jennifer McGuire says a study that looks only at mercury levels in seafood undermines the nutritional value of fish as a whole. Fish and other seafood are rich in omega-3 fatty acids and other nutrients that are good for both the heart and brain. Making healthy choices isn't that hard.
"You don't have to keep track of it in this complicated manner," McGuire said. "Just eat a variety of fish and you're fine."
The U.S. Food and Drug Administration recommends most people eat fish twice a week. For women who are or may become pregnant, nursing moms and young children, the FDA recommends seafood twice a week -- half of that (a 6-oz. serving) can be albacore tuna -- and avoid shark, king mackerel, swordfish and tilefish.
Most Americans eat less than half the recommended amount of fish and seafood a week, McGuire said, adding that low omega-3 levels account for about 84,000 deaths each year in the United States.
The study's author, Edward Groth III, is a risk analysis consultant who previously worked for 25 years at Consumers Union, the publisher of Consumer Reports magazine. He claims that "most consumers have no idea which fish are high in mercury and should be avoided, or which are low in mercury and are safe to consume."
Tuna makes up 37% of the total mercury in the seafood supply, the study shows. High levels of mercury have been linked to birth defects as well as neurological and kidney problems.
"Canned tuna is the number one fish product consumed in the U.S. today at just under 3 pounds per capita per year," said Michael Bender, director of the Mercury Policy Project in a statement announcing the study's publication. "Based on these new findings, tuna is also the number one mercury exposure risk."
The study lists fish and seafood with low levels of mercury include shrimp, sardines, tilapia, scallops, mussels, clams, salmon, crabs, flounder, herring and catfish. Moderate mercury levels are found in canned light tuna, cod, lobster, haddock, bluefish and both freshwater and sea bass. Canned albacore tuna, marlin, orange roughy and fresh or frozen tuna have a high mercury level. The fish with the highest levels include swordfish, shark and bluefin tuna/tuna sushi.
Tuna tops in mercury exposure for fish eaters