Eating fish is good for health; that’s a main reason why Americans’ per capita fish and shellfish consumption has been steadily rising. High-fish diets are associated with lower risk of death from heart attack and stroke, and nutrients in fish are critical for prenatal and childhood brain development (Grandma was right; fish really is “brain food.”)
But some fish can also contain toxic contaminants, like methylmercury, which pose well documented risks to public health.
Are the benefits greater than the risks? That’s far from clear. While studies of people with high-fish diets have shown significant reductions in cardiovascular risk, those studies also suggest that for those people who eat higher-mercury fish—a minority—the mercury in their diet increases cardiovascular risk, offsetting much of the benefit. The evidence with respect to risks and benefits for prenatal brain development suggests strongly that methylmercury damage to the developing brain is greater than the benefit provided by fish nutrients.
Comparing the size of risks and benefits, for individuals or for the public as a whole, does not make much scientific sense, because the benefits and risks fall on different people. Anyone who eats fish probably gets some cardiovascular benefit, and brain development seems to benefit from maternal consumption of fish of any type. But risks fall most heavily on a small minority of the population, those who have the highest mercury exposure because they often eat higher-mercury fish. The proposition that moderate benefits to everyone make substantial risks to a small minority acceptable is ethically debatable, at best.
People can enjoy the benefits of a fish-rich diet, with minimal risks, by choosing low-mercury fish. For that to occur, consumers need to be aware of the risks posed by mercury, and they need to know the mercury content of different varieties of fish and seafood. Many efforts have been made to inform the public on these issues, and more are needed. But these educational efforts must compete with several seafood lobby fables that have sown confusion on this subject.
Fable: The benefits of eating fish far outweigh the minuscule risks from mercury.
Facts: This claim exaggerates what the scientific evidence shows, summarized above. It suggests that consumers should simply eat lots of fish, and not be concerned about mercury. That proposition rests on two false assumptions: (1) Fish is fish, that is, all fish are alike; and (2) Risk/benefit trade-offs are unavoidable.
All fish are definitely not alike. Fish and shellfish varieties vary by more than 100-fold in mercury levels, and also vary in their content of specific beneficial nutrients. Nine of the 11 most popular American fish and seafood choices are low in mercury.
See our list of low-mercury fish.
While two-thirds of the fish and shellfish Americans eat each year are low in mercury, several popular seafood varieties have well-above-average levels, and some are very high in mercury. Information on the mercury content of popular fish and shellfish varieties is widely available, for instance on the US FDA’s food safety web site, but doesn’t reach most consumers.
See our listing of fish and shellfish by mercury levels.
On the second point, risk/benefit trade-offs are not inevitable at all. By choosing low-mercury fish, people can gain the nutritional benefits of fish and simultaneously minimize mercury risks.
Fable: Pregnant women should eat lots of fish, because the benefits to their babies’ brains will far outweigh any risks from mercury.
Facts: Fish consumption does provide essential nutrients for brain development, but the evidence strongly suggests that the damage done by mercury to the developing brain is significantly greater than the benefits offered by fish nutrients. Women of childbearing age should eat fish, but should also be particularly aware of mercury risks and choose low-mercury fish. (See “Who should be concerned?”).
Mercury damage to prenatal brain development has been documented in epidemiological studies of populations with high-fish diets, in the Faeroe Islands and in New Zealand. Two recent studies, in Boston and New York City, tested children born to women who ate typical US diets, averaging just over one fish meal per week. Even in this typical American population, the children whose mothers had eaten higher-mercury fish showed adverse effects of mercury on brain development. These studies also showed beneficial effects for brain development of higher fish consumption, reinforcing the need for pregnant women to choose low-mercury fish.
Several low-mercury fish, including salmon, herring, tilapia, anchovies and sardines, are also rich in omega-3 fatty acids, fish nutrients essential for brain development.
While fish consumption has significant benefits for both individual and public health, many fish stocks are overfished, and fishing practices are often unsustainable. Most of the nutrients in fish can also be obtained from non-fish (plant) sources. These important issues are outside the scope of this discussion of mercury in fish, but to read more about them, visit the Got Mercury web site.