BOSTON, MASSACHUSETTS. Dementia is becoming increasingly common among elderly people. About 70% of all cases of the disorder are Alzheimer’s disease (AD). Advancing age, high blood plasma concentrations of homocysteine, a family history of dementia, and the presence of the apolipoprotein E epsilon-4 allele (alternative gene form) are all known risk factors for AD.
Now researchers at Tufts University report that a low blood plasma level of DHA (docosahexaenoic acid), found in fish oil supplements, also increases the risk of developing AD. Their study included 899 men and women free of dementia when entering the study (Framingham Heart Study). The median age of the participants was 76 years and they were followed up for an average of 9 years. During the follow-up period, 99 (11%) of the patients developed dementia (including 71 [72%] with AD). All participants had provided blood samples at the start of the study. Analysis of these samples showed that those with high levels of DHA in the phosphatidylcholine fraction of their blood plasma had a 47% lower risk (relative) of developing dementia and a 39% lower risk of developing AD than did the participants with lower levels (after adjustment for age, gender, homocysteine level, education level, and presence of the apolipoprotein E epsilon-4 allele). The researchers estimate that the intake of DHA, which is a main component of fish oil supplements, among participants with high plasma levels was about 180 mg/day. This amount of DHA can be obtained from eating 2-3 servings of fish per week or from supplementation with a high quality fish oil supplement.
Schaefer, Ernst J., et al. Plasma phosphatidylcholine docosahexaenoic acid content and risk of dementia and Alzheimer disease. Archives of Neurology, Vol. 63, November 2006, pp. 1545-50
Morris, Martha Clare. Docosahexaenoic acid and Alzheimer disease. Archives of Neurology, Vol. 63, November 2006, pp. 1527-28 (editorial)