Healthnotes Newswire (November 30, 2006)—Folk medicine has long held that fish is “brain food.” In recent years, findings from scientific studies have begun to corroborate this conventional wisdom. New research from the venerable Framingham Heart Study has shown that eating three or more servings of fish per week may significantly decrease risk of dementia in general and Alzheimer’s disease in particular.

The likely protective ingredient in fish is an essential fatty acid known as DHA (docosahexaenoic acid). “DHA appears to be important in affecting the risk of dementia,” said Ernst J. Schaefer, MD, of the Lipid Metabolism Laboratory, Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University. Dr. Schaefer was lead author on the new study. “We sought to determine whether DHA status is associated with the risk of developing dementia.”

For an average of 9 years, Dr. Schaefer and colleagues studied 899 men and women (typically about 76 years old at the start of the study) who were free of dementia. Ninety-nine people developed dementia during the study period (including 71 cases of Alzheimer’s disease). After adjusting for various risk factors (such as age, homocysteine levels, and genetic susceptibility), researchers found that those people who ate the most fish (three or more servings per week) were 47% less likely to develop dementia that those who ate less fish. That group was also 39% less likely to develop Alzheimer’s disease.

The results also suggest that fish is an important source of DHA. Participants with the highest DHA levels in their blood were those who ate the greatest amount of fish.

The major fatty acids in fish are DHA and EPA (eicosapentaenoic acid), but it is DHA that appears to improve brain function and protect against dementia. No such effect has even been demonstrated for EPA, although that fatty is well known to protect against cardiovascular disease and inflammation. Earlier studies have found low DHA content in the brains of people with Alzheimer’s disease.

“Dementia is a major cause of disability among the elderly,” said Dr. Schaefer. “These results show a protective effect of eating fish on the development of Alzheimer’s disease and other forms of dementia. In the future, it will be important to determine whether taking DHA supplements can decrease further mental deterioration in people with established dementia.”

DHA is especially high in fatty fish, such as salmon and tuna.

(Arch Neurol 2006;63:1545–50)