Framingham Study: High DHA Levels Linked to Lower Dementia Risk

Caroline Cassels

November 20, 2006

November 20, 2006 — Individuals with higher levels of docosahexaenoic acid (DHA) have a significantly lower risk of developing dementia and Alzheimer's disease (AD), a new study suggests.

Researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, in Boston, Massachusetts, found individuals with the highest DHA levels had a 47% reduction in all-cause dementia and a 39% lower risk of developing AD.

"In our study, the correlation between DHA content and fish intake was significant, indicating that fish intake is an important source of dietary DHA," the authors write.

The study is published in the November 13 issue of Archives of Neurology.

Led by Ernst Schaefer, MD, the 9-year prospective follow-up cohort study analyzed completed dietary questionnaires and DHA blood levels of 899 study subjects who were participating in the Framingham Heart Study.

Neuropsychological testing revealed that all study participants were dementia-free at baseline. Thereafter, subjects had their cognitive function tested every 2 years using the Mini-Mental State Examination (MMSE). Those who experienced a decline of 3 or more points on the MMSE from the most recent exam were called back for a neurological and neuropsychological examination.

Study Strengths

The study population was 36.5% male and had an average age of 76 years. Plasma samples were measured for plasma phosphatidylcholine (PC) fatty-acid content. In addition, a subgroup of 488 patients completed dietary questionnaires.

During the study period, 99 of 899 subjects developed dementia, including 71 cases of AD. After controlling for age, sex, plasma homocysteine levels, apolipoprotein E4 allele, and education level, researchers divided individuals into quartiles according to their PC DHA levels. Those in the upper quartile experienced a significantly lower risk of all-cause dementia and AD compared with participants with levels in the lower 3 quartiles, the authors report.

Furthermore, the authors report, of the study participants who completed the dietary questionnaire, those in the top quartile reported consuming an average of 0.18 g of DHA per day and an average of 3 servings of fish per week.

"Our study is the first prospective analysis to assess the predictive value of plasma PC DHA content in the occurrence of dementia and Alzheimer's disease. Its strengths lie in its prospective design, its long follow-up period, the size of the sample, and the analysis of dietary data along with the direct assessment of the association between dementia and plasma phospholipid fatty-acid content," they write.

Are Supplements Protective?

The investigators also note that future research should focus on determining whether the combination of dietary supplementation with DHA can prevent further mental deterioration in patients with established dementia.

According to an accompanying editorial, by Martha C. Morris, ScD, from Rush University Medical Center, in Chicago, Illinois, this study is "the first evidence that direct measure of DHA in human plasma is related to lower Alzheimer's disease risk."

Studies done during the 1980s and 1990s found that DHA is important for learning ability and memory in early life, she notes. However, it is only recently that omega-3 fatty acids have been investigated for their importance to the aging brain.

While research indicates that consuming more DHA in the diet later in life increases DHA levels in the aging brain, Dr. Morris points out that more research is needed to definitively determine whether omega-3 supplements can prevent dementia.

Arch Neurol. 2006;63:1545-1550, 1527-1528.

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