Background: Epidemiologic and animal studies have suggested that dietary fish or fish oil rich in omega-3 fatty acids, for example, docosahexaenoic acid and eicosapentaenoic acid, may prevent Alzheimer disease (AD).

Objective: To determine effects of dietary omega-3 fatty acid supplementation on cognitive functions in patients with mild to moderate AD.

Design: Randomized, double-blind, placebo-controlled clinical trial.

Participants: Two hundred four patients with AD (age range [mean ± SD], 74 ± 9 years) whose conditions were stable while receiving acetylcholine esterase inhibitor treatment and who had a Mini-Mental State Examination (MMSE) score of 15 points or more were randomized to daily intake of 1.7 g of docosahexaenoic acid and 0.6 g of eicosapentaenoic acid (omega-3 fatty acid–treated group) or placebo for 6 months, after which all received omega-3 fatty acid supplementation for 6 months more.

Main Outcome Measures: The primary outcome was cognition measured with the MMSE and the cognitive portion of the Alzheimer Disease Assessment Scale. The secondary outcome was global function as assessed with the Clinical Dementia Rating Scale; safety and tolerability of omega-3 fatty acid supplementation; and blood pressure determinations.

Results: One hundred seventy-four patients fulfilled the trial. At baseline, mean values for the Clinical Dementia Rating Scale, MMSE, and cognitive portion of the Alzheimer Disease Assessment Scale in the 2 randomized groups were similar. At 6 months, the decline in cognitive functions as assessed by the latter 2 scales did not differ between the groups. However, in a subgroup (n = 32) with very mild cognitive dysfunction (MMSE >27 points), a significant (P<.05) reduction in MMSE decline rate was observed in the omega-3 fatty acid–treated group compared with the placebo group. A similar arrest in decline rate was observed between 6 and 12 months in this placebo subgroup when receiving omega-3 fatty acid supplementation. The omega-3 fatty acid treatment was safe and well tolerated.

Conclusions: Administration of omega-3 fatty acid in patients with mild to moderate AD did not delay the rate of cognitive decline according to the MMSE or the cognitive portion of the Alzheimer Disease Assessment Scale. However, positive effects were observed in a small group of patients with very mild AD (MMSE >27 points).

PMID: 17030655

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