Study shows fish protects women against stroke
BOSTON, MA, January 17, 2001 - The omega-3 fatty acids found in most
fish seem to protect women against the most common forms of stroke,
researchers at Boston's Brigham and Women's Hospital reported in Wednesday's
Journal of the American Medical Association.
Women can cut their risk of thrombotic stroke, which accounts for
between 40 and 50 per cent of all strokes, almost in half by eating
fish two to four times a week, the authors say.
"The clinical message I would boil down would be that women who had
a higher intake of fish had less stroke and that including fish as part
of a healthy diet would be something that you can do perhaps, to help
decrease your risk of stroke," said co-author Dr. Kathryn Rexrode, an
internist.
The article suggests most fish, even shellfish, help reduce the risk
of what's called ischemic stroke, which is caused by a blood clot that
forms either in an artery in the brain (thrombotic stroke) or elsewhere
in the body (embolic stroke) and moves to the brain.
Ischemic strokes make up about 83 per cent of all strokes, which can
cause temporary or permanent brain damage, affecting speech, co-ordination
and movement.
Fish high in omega-3 fatty acids -- tuna, mackerel, salmon, sardines,
bluefish, swordfish -- offer the most protection, Rexrode said from
Boston.
The findings may cause confusion among consumers, coming as they do
closely on the heels of recommendations from both the Canadian and U.S.
governments that people restrict their intake of certain types of fish
because they contain high levels of mercury.
The fish named? Tuna (steaks, not canned), shark, king mackerel and
swordfish, a spokesman for Health Canada said.
Children, women of childbearing years and pregnant and nursing women
are particularly at risk from mercury exposure and have been urged to
limit their intake of these kinds of fish to once a month, Health Canada
said. Other people should not eat these types of fish more than once
a week.
John Salminen is the head of the chemical health hazard assessment
division of Health Canada's food directorate. He said people who want
to increase their fish intake should try to work a variety of fish into
their diets.
"Don't focus on the particular species that we raised concerns about,"
he said. "There are many other species out there that are perfectly
safe. We have confidence in the supply of commercial fish sold in Canada
and those should be perfectly fine to consume."
The fish and stroke study was led by Hiroyasu Iso of the Channing Laboratory
of Brigham and Women's, a teaching hospital affiliated with Harvard
Medical School. The study says nothing about whether fish protects men
against stroke because it is based on data from the nurses' health study,
a massive, long-term survey of nearly 80,000 female nurses from 11 U.S.
states. Iso's team followed the women from 1980 to 1994.
During that time, 574 strokes were documented. Of those, 303 were
ischemic strokes, 181 were hemorrhagic strokes (when blood vessels in
or around the brain break or hemorrhage) and 90 were strokes of an undetermined
nature. When the researchers compared the diets of those women who had
strokes against those who did not, the benefits of a diet containing
fish became apparent. Women who ate fish once a week were 22 per cent
less likely to have a stroke. Those who ate it between two and four
times a week were 27 per cent less likely to have a stroke. And those
who ate it five or more times a week had their risk of stroke reduced
by 52 per cent.
There was no evidence that fish consumption reduced the risk of hemorrhagic
stroke. The research team isn't sure what it is about fish that protects
against stroke, but they believe it is the omega-3 fatty acids they
contain.
Rexrode said test-tube studies have shown that omega-3 fatty acids
inhibit platelet clotting or build up, which can lead to strokes.
-Source: The Canadian Press View abstract from the Journal of the
American Medical Association (JAMA)
View abstract online at: www.jama.ama-assn.org
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