Alzheimer's
Risk Lowered with Fatty Acid in Fish
Persons with diets rich in fish have a significantly lower
risk of dementia and Alzheimer's disease, according to a report in the Archives
of Neurology.
The key appears to be an omega-3 polyunsaturated fatty acid
called docosahexaenoic acid (DHA) that is linked to the reduction of dementia
risk and appears to be important for the proper functioning of the central
nervous system.
"If you have a high level of DHA, a fatty acid found in
fish, it reduced your risk of dementia by about half," says study lead researcher
Dr. Ernst J. Schaefer, at Tufts University in Boston.
It is known that omega-3 fatty acids protect the heart and
the circulatory system.
"Just as fish is good for your heart, it's probably good
for your brain as well," says Dr. Schaefer.
Fatty fish like mackerel, lake trout, herring, sardines,
albacore tuna, and salmon are high in DHA.
In the study, Dr. Schaefer collected data on DHA levels
and dementia in 899 men and women who were part of the Framingham Heart Study.
Over nine years of follow-up, 99 people developed dementia,
including 71 with Alzheimer's disease.
The researchers found that persons with the highest blood
levels of DHA had a 47 percent lower risk of developing dementia and a 39 percent
lower risk of developing Alzheimer's, compared with those with lower DHA levels.
Levels of DHA in the blood vary by how much the liver converts
alpha-linolenic acid, an essential fatty acid, to DHA and also by the amount
of DHA in the diet, say the researchers.
Persons with the highest blood levels of DHA said they ate
an average of two to three servings of fish each week. Persons with lower DHA
levels ate substantially less fish
Dr. Schaefer thinks the same benefit can be realized by
taking fish oil supplements.
"Everything that we know suggests that supplements would
be as effective as eating fish," he says. "Since low fish intake appears to
be a risk factor for developing dementia, either eat more fish or use one or
two fish oil capsules a day."
However, Dr. Schaefer adds that a randomized clinical trial
is still needed to see if DHA really protects the brain from dementia.
Martha
Clare Morris, Sc.D., at Rush University Medical Center in Chicago comments
in an accompanying
editorial, "This is the first study
to link blood levels of DHA to protection against Alzheimer's disease.
Dr. Morris, an epidemiologist, explains that recent animal
studies have shown that DHA reduces amyloid plaques - a hallmark of Alzheimer's
- in the brain and also improves memory.
"There is a lot of animal and biochemical evidence to support
what this new study shows," says Dr. Morris.
But, she says, she is not sure there is enough data to suggest
the value of fish oil supplements.
"It looks like the protective benefits from omega-3 fatty
acids are at a very low level,” she says. “There is very little
evidence that you get better protection from higher intake. Whether fish oil
supplements are protective is yet to be seen."
Another expert suggests clinical trials are needed to see
if DHA really protects against Alzheimer's.
"This shows in a prospective study that DHA is the only
plasma lipid to cut the risk for developing dementia a decade or more later," says
Greg M. Cole, Ph.D., at UCLA's David Geffen School of Medicine.
This
apparent protection is associated with eating fish, Cole says. "Other studies
have pointed to fish intake as protective but have been far less clear that
the
omega-3 fatty acids in fish were the factor associated
with risk reduction.
"This matters because if it is the fat, you could take fish
oil supplements and avoid mercury contamination issues," he concludes.
Always consult your physician for more information.
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