Diagnosis: Mercury

Nine years ago, Jane Hightower was simply a doctor with a bustling practice in internal medicine and 2-year-old twins at home. But when she started seeing patterns in her patients' symptoms-commonalities that included fainting, headaches, hair loss, and trouble concentrating-things began to change. All the standard lab tests were negative, and the San Francisco doctor found herself with a medical mystery on her hands.

Her first breakthrough came when a colleague told her about a patient who complained of hair loss after eating fish from a lake polluted with mercury. High-tower tested her patients for mercury, and sure enough, many of them had elevated levels of the neurotoxin in their bloodstream. Diagnosis: Mercury is a firsthand account of her attempts to bring her patients back to health. It is also an exposé of the federal agencies and industry lobbyists who put them at risk.

To start, Hightower needed to figure out how her patients had been exposed to mercury. She went back to them with more questions until another common factor emerged: they all liked seafood-a lot. Hightower diagnosed them with what she called "fish fog," and as word of her work spread, other doctors sent her more patients with similar symptoms. Over a one-year period she tested 123 patients and found that 89 percent had elevated levels of mercury in their blood. They were an unusual high-risk group: affluent, health-conscious consumers who shopped at gourmet markets and ate plenty of fish-a good thing, right? 

When Hightower asked the next logical questions-how much mercury is harmful to human health, and how much fish is too much?-she found no clear answers. Her trusty Cecil Textbook of Medicine recommended a maximum level of 50 micrograms of mercury per liter of blood, but the Environmental Protection Agency (EPA) standard was 5 micrograms per liter, and the Food and Drug Administration (FDA) claimed anything up to 200 micrograms was acceptable. Under the EPA standard, a 132-pound adult could safely eat less than one can of albacore tuna a week, compared with 28 cans under the FDA guidelines.

Mercury is concentrated in fatty tissues as it moves up the food chain, which means that large, predatory fish contain more mercury than the little fish they eat. In late 2000, the FDA advised pregnant women and women of childbearing age to eat fish such as shark and swordfish no more than once a month and suggested that other people eat no more than seven ounces (about one serving) of high-mercury fish species a week. Hightower tried a simpler approach: she told patients to stop eating fish for six months, which brought their blood mercury levels down and resolved nearly all of their symptoms.

Over the next year, the EPA and FDA started issuing joint advisories, expanding the category of people at high risk to include small children. But Hightower was seeing symptoms of mercury exposure in patients who weren't supposed to be at risk, such as otherwise healthy bodybuilders and fellow doctors.

Worried that many people were increasingly exposed to the neurotoxin, Hightower decided to publicize her findings by writing articles for medical journals. She also pushed the California Medical Association to recognize methylmercury as a hazard in seafood and to advise doctors to warn their patients accordingly; the group passed a resolution to do so in 2003. She continued to research the effects of mercury on human health and found that the electric-power industry (a major source of airborne mercury emissions) and seafood trade groups were both working to downplay health risks from mercury. In 2006, the tuna industry went so far as to argue before a California superior court that the state's attempts to require warning labels on canned tuna were illegal because they were at odds with FDA guidelines and, further, that the mercury found in fish was simply natural. The court ruled in the industry's favor.

It's true that many types of seafood provide important health benefits, and current federal advisories urge consumers to eat fish while avoiding high-mercury species. But as Hightower sees it, the government's warnings are confusing and leave many Americans at risk. She asserts that the FDA, which has jurisdiction over food safety warnings, should follow the EPA's example and identify a safe blood-mercury level for humans, and then calculate how much seafood an individual can reasonably eat. Hightower's patients have her sound advice to guide them, but the rest of us do not. Hightower is right-we could use a little help.

[Editor's Note:  Unlike many other contaminants, mercury concentrates not in fatty tissue but in muscle and other tissue. Mercury does indeed move up the food chain and is found at highest levels in predatory fish.]