Harvard Health Letter

On the brain: The brainy omega-3 fails an Alzheimer's test

Numerous studies have identified a correlation between higher consumption of the omega-3 fats contained in fish and fish oil and a lower risk of dementia and cognitive decline. Dig a little deeper, and one of the two main omega-3s, docosahexaenoic acid (DHA), seems to deserve most of the credit. Donepezil (Aricept) and other cholinesterase inhibitors are the most common treatment for mild to moderate Alzheimer's disease. But, at best, they somewhat slow down the pace at which Alzheimer's gets worse, and the side effects are a problem. With the lack of effective treatment and DHA's promise — and low cost — a study to see if the omega-3 might benefit people in the early stages of Alzheimer's disease would seem worth a try.

The Alzheimer's Disease Cooperative Study (ADCS), a consortium of Alzheimer's disease clinics with funding from the federal government to run clinical trials, conducted a high-quality (randomized, double-blinded, placebo-controlled) trial of DHA. About 400 patients with mild-to-moderate Alzheimer's were assigned to take either 2 grams of DHA derived from algae or a placebo pill every day for 18 months. (Algae-derived DHA is becoming popular because of concerns about overfishing and contamination with pollutants and the growing number of people adhering to vegan diets.) The study participants took a battery of tests to measure attention, language, and other cognitive abilities at the beginning and end of the study.

The results, published in November 2010 in the Journal of the American Medical Association (JAMA), showed no benefit from taking DHA. The scores on the cognitive function tests were, on average, the same for people in the DHA group and those in the placebo group. MRI scans of the brains of a third of the people who completed the study also showed no difference between the two groups.

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