DHA or Mercury: The Fish Dilemma

The more fatty fish you eat, the more DHA you get, with conservative recommendations suggesting we need at least two servings of fatty fish a week. But here comes the dilemma: fish also is one of the most concentrated sources of mercury, a metal that is toxic to nerve cells. The more mercury you eat, the lower your brain function.

In a study where fish intake was assessed in a group of men, women and children, about one in five participants warranted testing for mercury either because of high intakes of fish or because they were showing signs of mercury poisoning (i.e., fatigue, reduced memory and/or joint pain). Results showed that the mercury level for all women was 10 times that found in the general public, and some children had more than 40 times the national average. Almost all participants had blood mercury levels above 5 micrograms per liter, the maximum level recommended by the U.S. Environmental Protection Agency (EPA). Up to 18% had levels greater than 20 micrograms per liter. People with the highest mercury levels also reported eating greater amounts of swordfish, ahi and other fish known to be high in mercury.

Fortunately, these dangerously high mercury levels were reversible, although it took almost ten months to reach acceptable levels and required stopping or greatly reducing consumption of fish. The findings were so shocking that the researchers recommend that questions regarding fish consumption should be part of all comprehensive health screenings. The results of this study and others confirm that the more fish you eat, the more likely you are to consume too many mercury.

You need fish to get your DHA, but that same fish also supplies a nerve-damaging metal. One way to get around the mercury problem is to choose fish that are lower in this toxic metal, such as salmon and canned light tuna. One study even found that these high-DHA fish help block the damaging effects from mercury on the nervous system. White-meat fish, such as cod, halibut or haddock, are relatively low in mercury but also have little of those mood-boosting omega-3s. So you don’t get much benefit or harm from eating them. Definitely stay away from the biggest mercury offenders, such as swordfish, albacore or ahi tuna, shark, mackerel and tilefish. Or look for foods that are fortified with DHA.