Mercury and Health

As our understanding of the potential effects of mercury on health has grown—particularly as it relates to fish consumption—so too has confusion, misinformation and even fear about fish safety. Arbitrary and inconsistent food warnings and fish advisories, though well meaning, have stoked this fear and concern to the point that consumption of fish—one of the most health-beneficial foods available—is declining.

U.S. power plants are scrutinized when worried consumers become concerned about mercury levels in fish.  However, the tuna, swordfish and other species of fish served on Illinois dinner tables are caught in oceans far away from Illinois power plants.

The U.S. Environmental Protection Agency (USEPA) has concluded that mercury from U.S. industry is responsible for very little of that contained in the nation's waters. Most mercury is naturally occurring. Asia is the global leader in emissions resulting from human activities and is responsible for most of the mercury that lands in U.S. waterways.

The form of mercury that is the focus of health concerns is methylmercury.  Mercury from the air and other natural sources can be converted to methylmercury in the water, where it can enter the food chain through fish. Methylmercury cannot be inhaled. A potential health risk could result, however, if large enough quantities of methylmercury are ingested, with pregnant women, women of childbearing age, and children the subjects of greatest concern.

In a 2005 Centers for Disease Control study of methylmercury levels in the U.S. population, however, none of the people studied, including children, had levels that were high enough to place them at risk.  While USEPA’s advisory thresholds are set at one-tenth of the actual risk concern level, none of the children even reached this threshold, and only one woman barely exceeded the threshold.

Depending on the types and quantities of fish they eat, women of childbearing age can enjoy fish as part of their regular diets, as long as they follow federal guidelines. The U.S. Food and Drug Administration (FDA) has worked with USEPA to develop advice for consumers regarding methylmercury and fish consumption. That advice warns pregnant women not to eat shark, swordfish, king mackerel or tilefish because they may contain high levels of methylmercury. Still, pregnant women are advised to eat up to 12 ounces (two average meals) a week of a variety of fish and shellfish that are low in mercury, such as shrimp, canned light tuna, salmon, pollock and catfish.

Experts agree that eating less fish poses more of a health concern than eating fish with trace amounts of mercury. Eating less fish can actually increase risk of stroke and heart disease.

A study from the Harvard School of Public Health confirmed that the cardiovascular benefits of omega-3 fatty acids in fish far outweigh any risks of negligible mercury exposure. Children also benefit from fish, with those who eat fish regularly performing better on tests of brain development than those who do not. A study conducted by Dr. Joseph Hibbeln with the National Institutes of Health and described recently in The Economist links the amount of omega-3s in a pregnant woman’s diet to her child’s intelligence, fine-motor skills and social behavior.

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Children also benefit from fish, with those who eat fish regularly performing better on tests of brain development than those who do not. A study conducted by Dr. Joseph Hibbeln with the National Institutes of Health and described recently in The Economist links the amount of omega-3s in a pregnant woman’s diet to her child’s intelligence, fine-motor skills and social behavior.

The study found that children of women who had consumed the smallest amounts of omega-3s during their pregnancies had lower-than-average verbal IQs and higher levels of pathological social interactions. Dr. Hibbeln concludes that the benefits of eating omega-3-rich fish are greater than the risks from the mercury in them. 

Dr. Hibbeln cites “frightening” data that showed how 14 percent of seven-year-olds whose mothers consumed the lowest intake of omega-3s during pregnancy exhibited anti-social behavior, compared to 8 percent of the children of women with the highest omega-3 intake levels.  The same article cites two studies linking a decrease in omega-3 and omega-6 consumption with an increase in mental illness.