posted 01/02/03
Men 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 new
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 stroke and heart attack. What is surprising
about this one is that it shows how little fish — one to three meals a month of
virtually any fish or shellfish, like salmon, sushi, tuna on rye, broiled
lobster or 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 released last week 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 followed for 14 years reported in The Journal of the American Medical
Association in January found 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 once a
month. But 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 he said he could not explain why his study
found a threshold level, while the other study found a progressive benefit.
Dr. He's study also deepened a mystery that has
stymied 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: is it
some other component of fish, some combination, or what?"
Dr. Daviglus did agree with the general
conclusion 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 she 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, like that found in fish sticks and fast-food restaurants.
The fried breading is full of salt and transfatty
acids, which have been associated with heart disease, Dr. He said.
Although fatty, dark-fleshed fish are the richest
in fish oils, Dr. He's study found that even men who ate light-fleshed shrimp
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 in 1986, when they were ages 40
to 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 like
mackerel, salmon or sardines; other fish, like flounder, cod and hake; or
lobster, shrimp or scallops as a main course.
Dr. He's 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 a pool of 43,671 men whose histories Dr. 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.
Dr. He adjusted his figures for factors like
smoking, age, aspirin use, lack of exercise, high cholesterol 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.
Source: Diabetes In Control Dot Com.
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