8 July, 2003

However, wild fish eaten raw excretes more Mercury than when it is cooked as the damaged fats are harder for the body to process.

Chris Gupta

A diet full of fish could mean a diet full of mercury

By Jane E. Allen
Los Angeles Times

Mercury poisoning. Mercury occurs naturally but is mostly a byproduct of coal-burning, mining and other industries. Once in the water supply, it forms methyl mercury, which lingers in fish flesh, making predator fish such as swordfish and halibut the most toxic.

Lee Flynn thought she had a healthy lifestyle. She was thin and active and she ate well with lunches of tuna and fresh vegetables and dinners of halibut, sea bass or swordfish.

Yet she spent more than a decade plagued by fatigue, stomachaches and headaches, as if she had "a wicked hangover." Her hair started falling out. Memory lapses made her think she was losing her mind.

"I really felt something was poisoning me, but I couldn't find the source," said Flynn, 59.

The Sausalito, Calif., anthropologist and documentary filmmaker eventually ended up in the office of Dr. Jane Hightower, a San Francisco internist. When Hightower heard that Flynn was eating fish nine times a week, she immediately ordered a blood test for mercury. A heavy metal that accumulates in the flesh of fish, especially the popular predatory varieties, mercury can also accumulate in people who eat those fish.

The test's stunning result: Flynn's mercury level was 20.6 micrograms per liter of blood. A safe level is about 5, according to the federal Environmental Protection Agency.

Like Flynn, many adults and children may be unwittingly overdosing on mercury, say Hightower and some public-health activists, and it's likely that most of them are going undiagnosed.

In recent years, fish has become the food of choice for millions of Americans trying to eat more healthfully, with per capita consumption at about 15 pounds, a 20 percent increase since 1980.

People on weight-loss diets turn to fish as a lean alternative to beef. Bodybuilders go for the protein; it's not unusual for them to polish off entire cans of tuna. Others are drawn to the cardiovascular benefits of omega-3 fatty acids in fish. Restaurants, meanwhile, are expanding their portions, often serving as much as a pound at a time (a normal portion is 3 or 4 ounces).

The health benefits are undeniable and some people may suspect the warnings are overblown. Last month, researchers at the American Psychiatric Association meeting announced that fish rich in omega-3s may prevent depression late in pregnancy and after childbirth. A study a week earlier in the journal Lancet found that children in the Seychelles Islands whose mothers ate a lot of fish during pregnancy showed no signs of health problems.

Not all doctors 'think fish'

Even though the federal government and the state of Washington have advised pregnant women to limit their fish intake, some people still don't get the message or don't understand the cumulative effects. Furthermore, physicians aren't trained to "think fish" when patients complain of mental fuzziness, fatigue, hair loss and tingling hands and feet. Those symptoms also can point to thyroid problems, multiple sclerosis, chronic fatigue syndrome or menopause.

Last November, Hightower published a report in the online journal Environmental Health Perspectives, a publication of the National Institutes of Health, on 123 patients, 89 percent of whom had excessive mercury she traced to fish.

The study was one of the first to document mercury levels in people eating more than two servings of fish a week. To date, Hightower has documented 300 cases of elevated mercury levels in her patients, including a 4-year-old girl practically living on canned tuna.

"Mercury is a known poison," Hightower says. "By definition, this means it is harmful and can make one ill or even kill."

Predators are most toxic

Mercury occurs naturally, but is mostly a byproduct of coal-burning, mining and other industries. Once in the water supply, it forms methyl mercury, which lingers in fish flesh. As big fish eat smaller fish, they absorb more of the heavy metal, making predators such as swordfish, shark, tuna and halibut among the most toxic; smaller fish such as salmon and shellfish the least.

Although fresh tuna tends to have more mercury than canned varieties, levels in canned tuna can vary from nearly undetectable to 1 part per million, the level beyond which the Food and Drug Administration prohibits its sale.

Methyl mercury is especially damaging to the developing brains of fetuses and children. The FDA advises pregnant women to eliminate shark, tilefish, king mackerel and swordfish, and limit eating of other fish to 12 ounces a week.

The state of Washington recommends pregnant women also eliminate fresh or frozen tuna steaks and restrict their intake of canned tuna.

But high mercury levels don't always produce symptoms.

Clarissa Lee, a 30-year-old preschool teacher from San Francisco, was eating lots of swordfish, sea bass and halibut last summer while visiting Boston, Martha's Vineyard and the Hamptons.

In August, she told her gynecologist that she and her husband wanted to have a baby. The doctor heard about her fish consumption and ran a mercury test. Lee's level was 37. Lee gave up fish for a while, got her mercury levels down and now indulges in the occasional salmon.

As for Flynn, she gave up fish for almost two years. She now eats fish a couple of times a month, but never touches the predators. Her mercury levels are normal, her memory is back and she feels good.

"Do anything to excess," Lee says, "and that's when you get into trouble."

Fish ranked by mercury levels

Americans are consuming more fish, a good source of low-fat protein. But with increased consumption comes the potential for higher exposure to mercury, a toxic heavy metal. Some fish are more likely to contain high levels of mercury. Here are some examples.

The worst: These fish have the highest mercury levels. Pregnant women, nursing mothers and small children are advised to avoid them. King mackerel, shark, swordfish, tilefish, tuna.*

In between: These fish can be high in mercury; they should be consumed only occasionally. Halibut, lobster, mahi-mahi, orange roughy, red snapper.

The best: These fish tend to have the lowest mercury levels. But some may still contain other contaminants, including PCBs. Catfish, flounder, sole, salmon, sardines, shellfish (includes clams, crab, oysters and shrimp), tilapia.

*The state of Washington includes tuna on its list of fish that pregnant women should avoid; the federal government puts it on the in-between list.

Sources: USDA Office of Seafood; Food and Drug Administration; Environmental Protection Agency; Washington State Department of Health