Higher level of certain fatty acid (DHA) associated with lower dementia risk

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Public release date: 13-Nov-2006

http://www.eurekalert.org/pub_releases/2006-11/jaaj-hlo110906.php]

Contact: Siobhan Gallagher

JAMA and Archives Journals

Higher level of certain fatty acid associated with lower dementia risk

Individuals who have higher levels of a fatty acid known as

docosahexaenoic acid (DHA) in their blood may have a significantly lower

risk of developing dementia and Alzheimer's disease, according to a

report in the November issue of Archives of Neurology, one of the

JAMA/Archives journals.

Age, family history and genetic factors have all been found to increase

the risk of dementia and Alzheimer's disease, a neurodegenerative

disorder that causes 70 percent of cases of dementia in the elderly,

according to background information in the article. Recent studies have

found that high levels of homocysteine, an amino acid that is derived

from proteins in the diet and that can accumulate in the blood and

contribute to heart disease, increase the risk for Alzheimer's disease

and dementia. In addition, DHA, an omega-3 polyunsaturated fatty acid

found in fish, appears to affect dementia risk and to be important for

the proper functioning of the central nervous system.

Ernst J. Schaefer, M.D., Mayer U.S. Department of Agriculture Human

Nutrition Research Center on Aging at Tufts University, Boston, and

colleagues studied the association between DHA levels and dementia in

the blood of 899 men and women who were part of the population-based

Framingham Heart Study. The participants of an average age of 76 years

provided blood samples and underwent neuropsychological testing, and

were followed for an average of nine years. A subgroup of 488 also

filled out a questionnaire assessing their diet, including information

about fish consumption. None of the participants had dementia at the

beginning of the study; and they were given a mental examination every

two years to screen for its development.

Through the nine-year study period, 99 out of 899 participants developed

dementia, including 71 with Alzheimer's disease. After controlling for

other known risk factors for dementia, including age and homocysteine

levels, and dividing the study population into fourths (quartiles) based

on levels of DHA, the researchers found that men and women in the

quartile with the highest DHA levels had a 47 percent lower risk of

developing dementia and 39 percent lower risk of developing Alzheimer's

disease than the other three quartiles with lower DHA levels. Among the

participants who completed the dietary questionnaire, those in the top

quartile of blood DHA levels reported that they ate an average of .18

grams of DHA a day and an average of three fish servings a week.

Participants in the other quartiles ate substantially less fish.

DHA levels in the blood vary by the degree to which the liver converts

alpha-linolenic acid, an essential fatty acid, to DHA and also by the

amount of DHA in the diet. " In our study, the correlation between

[blood] DHA content and fish intake was significant, indicating that

fish intake is an important source of dietary DHA, " the authors write.

" In the future, it will also be important to determine whether combined

dietary supplementation with DHA can decrease further mental

deterioration in patients with established dementia, " they conclude.

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Arch Neurol. 2006;63:1545-1550.

Editor's Note: Please see the article for additional information,

including other authors, author contributions and affiliations,

financial disclosures, funding and support, etc.

Editorial: Link Between Fatty Acids and Dementia Makes Biological Sense

There is a strong basis in biology for the neuroprotective effects of

DHA, writes Martha Clare , Sc.D., Rush University Medical Center,

Chicago, in an accompanying editorial.

Lipids, a collective term for fats and oils, make up about 50 to 60

percent of the brain's dry weight, and DHA is the most abundant fatty

acid found in the cell membranes of the brain's gray matter, she writes.

Studies done in the 1980s and 1990s found that DHA is important to a

variety of brain cell components and functions. " Indeed, the level of

DHA in the brain has been shown to be very important for learning

ability and memory in early life in studies of rodents, baboons and

humans, " Dr. writes. " It is only recently that the omega-3 fatty

acids have been investigated for their importance to the aging brain.

The DHA composition of the brain decreases with age as a result of

increased oxidative [result of oxygen exposure] damage to the lipid

membranes. "

Research indicates that consuming more DHA in the diet later in life

increases DHA levels in the aging brain. However, more studies are

needed to determine whether omega-3 supplements could prevent dementia,

she concludes.

(Arch Neurol. 2006;63:1527-1528.

--

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