Closing in on the Specific Omega-3 Fatty Acid

Earlier this year we reported the apparent preventive effect of eating fish on the risk of developing Alzheimer’s. Now a study published in the Archives of Neurology has taken things a bit further. Data from the Framingham Heart Study were tapped to show possible relationships between dietary and plasma contents of 8 omega-3 fatty acids and the risk of Alzheimer’s disease. One of these, docosahexaenoic acid (DHA), demonstrated such a relationship.

The study showed quite convincingly that plasma DHA predicted the occurrence of dementia, including Alzheimer’s disease, independent of age, sex, apolipoprotein E genotype, homocysteine, and education level; people who ate larger amounts of fish – an average of 3 servings a week – consumed about 0.18 grams/day of DHA and halved their risk of developing dementia over a 9-year period.

The actual level of DHA in the blood is derived from the conversion of alpha-linolenic acid to DHA in the liver, and from dietary DHA. The other omega-3 fatty acid contained in fish – eicosapentaenoic acid – plays no obvious role in preventing dementia. It’s fair to recommend that you try to eat fish (preferably fatty fish) at least twice a week; the benefits are likely to be considerably greater than the possible risk of excess mercury intake.