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http://www.nytimes.com/2002/12/24/science/24CND_FISH.html

Eating Fish Just Occasionally Can Help Ward Off Stroke

By DONALD G. McNEIL Jr.

en who eat seafood as seldom as once a month may cut their risk of the most common kind of stroke by more than 40 percent, a study by the Harvard School of Public Health has found.

Many studies over the last two decades have found that eating fish reduces the risk of heart attack and strokes caused by clogged arteries. What is surprising about this study is that it shows how little fish — one to three meals a month of virtually any fish or shellfish, from salmon sushi to tuna on rye to broiled lobster to McDonald's Filet-O-Fish — appears to produce the maximum benefit.

"Previous studies found that you had to eat fish once or twice a week," said Dr. Ka He, the Harvard nutritionist who led the study, which was made public today by the Journal of the American Medical Association. "And they found a linear association — the more fish you ate, the more benefit you got. But in our study, we found a threshold. Further fish did not provide further benefit."

A Harvard study of strokes among 80,000 female nurses who were followed for 14 years reported in the Journal of the American Medical Association in January that women who ate fish five or more times a week had a 52 percent lower risk of stroke than women who ate fish less than one a month. However, it found that the relative benefit dropped to only 22 percent for those who ate fish once a week and 7 percent for those who ate fish once a month.

Dr. He agreed that the protocols of the two studies were roughly the same and said he could not explain why his study had found a threshold level, while the other study found a progressive benefit.

Dr. He's study also deepened a mystery that has flummoxed nutritionists: it was believed for years that fish wards off heart disease and stroke because it is rich in omega-3 polyunsaturated fatty acids, and sales of fish oil capsules soared on this assumption. But this study, like other recent ones, found no definitive connection: fish with larger amounts of omega-3 fatty acids did not confer larger protection against stroke.

"Everybody continues to bark up the wrong tree," said Dr. Martha L. Daviglus, a preventive-medicine specialist at Northwestern University Medical School in Chicago, who led a 1997 study of fish and stroke risk in 1,800 employees of a Chicago electric company. "Everyone wonders: it is some other component of fish, some combination, or what?"

Dr. Daviglus did agree with the general conclusion that Dr. He's study reached: something in fish is good for the arteries and everyone should eat at least some fish each month.

Although the study did not reach conclusions about species or cooking methods, both Dr. Daviglus and Dr. He were quick to say that they thought it would be medically irresponsible to suggest that anyone eat only deep-fat-fried fish, such as that found in fishsticks and fast-food restaurants.

They would still get the benefits of the fish, Dr. He said, but the fried breading is full of salt and transfatty acids, which have been associated with heart disease.

Although fatty, dark-fleshed fish are richest in fish oils, Dr. He's study found that even men who ate light-fleshed shrimp or lobster two or three times a month had fewer strokes.

His study used data found in the Health Professional Follow-up Study, which includes 51,529 doctors, dentists, pharmacists and other health workers who joined it in 1986, when they were between the ages of 40 and 75. Every four years, they filled out detailed questionnaires about their habits, including fish consumption.

The questionnaires ask how often the men ate fish and whether it was one of four groups: canned tuna; dark meat fish such as mackerel, salmon, sardines, bluefish or swordfish; other fish, such as flounder, cod and hake; or lobster, shrimp or scallops as a main course.

The questionnaires did not ask whether the fish was raw, smoked, broiled or fried. "If your questionnaire is more than 20 pages, no one answers it," Dr. He said.

His group, which began its study two years ago, screened out all men who in 1986 had histories of stroke or heart disease, diabetes or obesity, leaving him with a pool of 43,671 men whose histories he analyzed for a 12-year-period. Over the years 1986 to 1998, 609 had strokes. Ischemic strokes — those caused by clogged cerebral arteries, which account for 80 percent of all strokes — seemed to be reduced by eating fish.

Rates of hemorrhagic strokes — those caused by burst blood vessels — were not affected.

Some researchers have worried that fish oils, which inhibit clotting, might cause more hemorrhages, but recent studies have not borne this out. Studies done in the 1980's showed that heart attacks and ischemic strokes were very low among Greenland Eskimos, who eat large amounts of fish fat, while their rates of hemorrhagic strokes were high. Recent studies, including Dr. He's, have not found higher rates of brain-bleeding among consumers of modest amounts of fish.

Dr. He adjusted his figures for factors like smoking, age, aspirin use, lack of exercise, high cholesterol, high blood pressure and use of high-blood pressure medicine, and concluded that men who ate one to three meals of fish a month had a 43 percent lower relative risk of ischemic stroke than men who ate fish less than once a month or never. Men who ate fish five or more times a week did not fare significantly better; their relative risk was 46 percent better.

Going over Dr. He's risk tables, Dr. Daviglus noted that Dr. He had found something that she also noticed in her many interviews with electrical company employees: "Every study shows that fish eaters are a very different kind of people," she said. Drawing attention to the column of numbers adjusting for the health habits of those who ate fish five times a week she said: "Look, they smoke less, they eat more food, they eat many more fruits and vegetables. Fish could just be a marker for how healthy you are."

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