Time To Scale Back On Big Fish?

High mercury levels may wind up harming the health-conscious eater

A middle-aged woman came to Dr. Jane Hightower's San Francisco internal medicine practice complaining of hair loss, upset stomach, and difficulty concentrating. Like many professionals in the Bay area, the woman ate a lot of fish. But that wasn't a concern -- not, at least, until Dr. Hightower sent the patient to a dermatologist, who knew hair loss could be caused by mercury poisoning. The dermatologist did a blood test, which showed four times the recommended limit for the metal. Weeks later, a second patient arrived at Dr. Hightower's office with similar symptoms. Another blood test was given. Again, mercury.

Suspecting she might be on to something, Dr. Hightower spent the next year analyzing 89 patients who reported eating a diet heavy in fish or had symptoms that could be linked to mercury toxicity. In the end, 82 tested above the 5 micrograms per liter widely used as the recommended limit for mercury in the blood.

Dr. Hightower's 2001 study on mercury toxicity was one of the first to identify this possible downside to Americans' growing appetite for fish. As more people heed the medical community's advice to eat fish often to ward off cardiovascular disease, they may be exposing themselves to high levels of mercury.

This is especially true for those who favor big predatory fish, such as swordfish, king mackerel, shark, tilefish, and tuna (although canned light tuna has lower levels than tuna steaks or canned albacore). Because methylmercury -- a potent form of mercury created by microbial action on mercury in polluted waters -- becomes more concentrated as it rises through the food chain, big fish that eat smaller ones have the most methylmercury. A chart on the Food & Drug Administration Web site (www.cfsan.fda.gov/~frf/sea-mehg.html) shows that swordfish has 14 times the concentration of mercury as catfish. Levels are low in scallops and crabs and are usually undetectable in salmon, oysters, and shrimp. (Farm-raised salmon, however, may be higher in another environmental toxin, PCBs.) Cooking has no effect on methylmercury, so it matters not whether you prefer your tuna grilled or wrapped raw in seaweed and rice.

So far, the FDA's consumer advisory addresses only the high-risk groups of pregnant women, those of child-bearing age, and their children. Mercury crosses the placenta and can damage the developing fetal brain, shaving points off IQ and causing shortened attention spans. Some doctors even speculate on a link between mercury toxicity and autism, and studies are looking at a possible connection. Meanwhile, the FDA and the medical community have long thought that commercial fish consumed in the U.S. don't have enough mercury to pose a problem for adult men or women not expecting to become pregnant, says Vasken Aposhian, professor of molecular and cellular biology at the University of Arizona and an expert on methylmercury.

Studies like Dr. Hightower's are challenging that assumption. The Centers for Disease Control reported last year that almost 8% of the 1,709 women of child-bearing age tested had blood mercury levels above 5.8 micrograms per liter (or 5.8 parts per billion), the amount consiered safe in umbilical cord blood by the Environmental Protection Agency. Other findings: Blood mercury levels rose with frequent fish consumption, and levels were greater among those with higher education (who presumably know the benefits of eating fish and can afford pricey sushi and game fish).

If a patient shows up with a string of symptoms that could indicate mercury toxicity, and a blood test confirms the diagnosis, what's the next step? Not all doctors agree. Dr. Hightower shifted her patients to fish with low mercury levels and watched their blood mercury readings drop into the acceptable range. "It's real easy," Dr. Hightower says. "You eat mercury, it goes into your blood. You stop, and the mercury levels go down." The body excretes mercury through feces, urine, sweat, hair, and nails. In fact, that's why many doctors think adults are not at great risk unless levels are extremely high. The half-life of mercury in the blood is two to three months for adults.

STORED METALS. But others see a more complicated -- and serious -- health problem. Even if the blood is readily cleansed, Dr. Richard Horowitz, an internist in Hyde Park, N.Y., says mercury can be stored in body tissue, including the brain. Dr. Horowitz, who treats many Lyme disease patients, says the symptoms of chronic Lyme disease mirror those for metal toxicity. He suspects some Lyme patients' continuing problems, such as fatigue, are linked to metals in their bodies. If so, that may explain why they don't get better when they take the antibiotics used to treat Lyme.

Dr. Horowitz does not rely on the standard blood test to diagnose the presence of mercury because it measures only recent exposure. Instead, he gives patients a chelating agent -- a chemical that binds to and pulls metals from tissues. He then measures the amount of mercury excreted in the urine. He also uses three-month regimens of alternating chelation, vitamins, and minerals to remove stored metals. He has seen symptoms ease in about 10% of those treated.

Such routine use of chelating agents is controversial. "Chelators are not benign drugs," points out Dr. Michael Shannon, an associate professor at Harvard Medical School. They can cause kidney and liver damage as well as allergic reactions.

Chelation might be an answer in extreme cases. For most of us, the remedy is simple. As one doctor advises: "Eat the little fish." How complicated is that?

By Carol Marie Cropper

    Before it's here, it's on the Bloomberg Terminal.