Omega-3 vetzuren tegen dementie.*
Een van de omega-3 vetzuren te weten DHA lijkt dementia en de ziekte van Alzheimer te kunnen voorkomen zo blijkt uit een Amerikaanse studie waarbij 899 ouderen negen jaar gevolgd werden. Omega-3 vetzuren,en DHA zitten vooral in vis en dan speciaal vette vis zoals forel, haring, sardines, tonijn, zalm en makreel. Mensen met de hoogste bloedwaarden DHA hdden 47% minder kans op het krijgen van dementie en 39% minder kans op de ziekte van Alzheimer. Een weinig DHA wordt in het lichaam gevormd uit alfalinoleenzuur (ALA) doch het meeste zal met de voeding binnen moeten komen. De mensen in deze studie met de hoogste bloedwaarden DHA bleken 2 tot 3 keer per week vis te eten in tegenstelling tot zij met de laagste bloedwaarden die geen of hooguit 1 keer per week vis aten.
DHA seems to offer protective effect in the brain, researchers report.
Adding
further weight to the theory that fish may be brain food, new research found
that people with diets rich in fish have a significantly lower risk of dementia
and Alzheimer's disease.
The key appears to be docosahexaenoic acid
(DHA), an omega-3 polyunsaturated fatty acid that appears to affect dementia
risk and 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,"
said study lead researcher Dr. Ernst J. Schaefer, senior scientist and director
of the Lipid Metabolism Laboratory at the Jean Mayer U.S. Department of
Agriculture Human Nutrition Research Center on Aging at Tufts University in
Boston.
It's 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," Schaefer said.
Fatty fish like mackerel, lake trout,
herring, sardines, albacore tuna and salmon are high in DHA.
The study findings are published in the
November issue of the Archives of Neurology.
In the study, Schaefer and his colleagues
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 people 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, the researchers noted.
People with the highest blood levels of DHA
said they ate an average of two to three servings of fish a week. People with
lower DHA levels ate substantially less fish, the researchers reported.
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 said. "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, Schaefer added that a randomized
clinical trial is still needed to see if DHA really protects the brain from
dementia.
Martha Clare Morris is an epidemiologist at
Rush University Medical Center in Chicago and author of an accompanying
editorial in the journal. "This is the first study to link blood levels of
DHA to protection against Alzheimer's disease," she said, adding 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," Morris said.
But, she said, she's 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. There
is very little evidence that you get better protection from higher intake,"
she said. "Whether fish oil supplements are protective is yet to be seen."
Another expert thinks 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," said Greg M. Cole, a neuroscientist at the Greater
Los Angeles VA Healthcare System and associate director of the Alzheimer's
Disease Research Center at UCLA's David Geffen School of Medicine.
This apparent protection is associated with eating fish, Cole said. "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," he said. "This matters because if it is the fat, you could take fish oil supplements and avoid mercury contamination issues." (Nov. 2006) (Opm. Meer over vetzuren of over vis.)