Fish and Your Health

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Our bodies can’t make omega-3s, so we need to get them from our diet. In aquatic ecosystems, omega-3s originate in the phytoplankton that fish eat. The fish with the highest levels of omega-3s are those that naturally live in cold waters, such as salmon, trout and herring. (Other good sources of these fatty acids include some leafy vegetables, eggs, nuts and oils.)

Unfortunately, industrial activities have introduced toxic substances into our waters. One such toxin is mercury, which can damage the nervous system, particularly the developing nervous systems of young children. In the 1990s, people took notice when the Food and Drug Administration (FDA) began warning consumers about the danger of eating fish contaminated with methyl mercury — a form of mercury that is absorbed easily into our bodies when we eat contaminated fish. Much of the mercury in our oceans comes from our fossil fuel-burning power plants. That mercury is consumed by fish, and the level of mercury increases as it moves up the food chain, concentrating in large, carnivorous fish such as sharks and swordfish. The FDA updated its warnings on mercury consumption in 2002 and again in 2004, and many concerned consumers opted to skip fish night. (See "Expert Advice for Choosing Fish," below.)

However, the FDA never intended to discourage the entire population from eating any kind of fish. The warnings specifically directed pregnant women and young children to avoid fish high in mercury.  In fact, many fish species are good sources of nutrition for pregnant women, because omega-3s play an essential role in developing cognitive function.

Although children’s nervous systems are the most vulnerable, the rest of us face the same issue: The evidence suggests that omega-3s improve brain function, but high mercury levels can damage it. Almost all of us can expect to suffer some mental decline as we age, but in a study of about 4,000 senior citizens conducted at the Rush University Medical Center in Chicago, researchers found that people over the age of 50 who ate fish once a week slowed their rate of mental decline by 10 percent. The rate was 13 percent slower for those in the study who ate twice as much fish every week.

Another study published in the Journal of the American Medical Association last spring found that, although the elderly can experience cognitive damage from exposure to methyl mercury, low levels are not particularly dangerous. Researchers tested 474 people who ate about 12 ounces of fish per week and found that the amount of mercury they consumed didn’t significantly affect clarity of thinking, memory or coordination.

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