The jury is still out regarding the benefit of the omega-3 fatty acid docosahexaenoic acid (DHA) in Alzheimer's disease, according to two double-blind multicenter clinical studies presented at the 2009 International Conference on Alzheimer's Disease, held from July 11 to 16 in Vienna, Austria.

Joseph Quinn, M.D., of Oregon Health & Science University in Portland, and colleagues performed a study which randomized 402 individuals diagnosed with mild to moderate Alzheimer's disease to 2 g/d of DHA or placebo over 18 months. Although DHA levels increased in the brains of patients receiving the supplement, there was no difference in the rate of change on tests of mental function, global dementia, daily living activities, or behavioral symptoms. DHA-treated patients who did not express the APOE ε4 gene, which increases the risk of developing the disease, did demonstrate a slower rate of mental function decline.

Karin Yurko-Mauro, Ph.D., of Martek Biosciences Corporation in Columbia, Md., and colleagues conducted a study which randomized 485 older healthy individuals with mild memory complaints to 900 mg/d of DHA or placebo over six months. At study completion, individuals in the DHA group made modest but significantly fewer errors on a visuospatial episodic memory test compared with the beginning of the study (−1.63 ± 0.76).

According to an Alzheimer's Association statement, the studies together "raise the possibility that treatments for Alzheimer's must be given very early in the disease for them to be truly effective," emphasizing the need for earlier detection and diagnosis.

Authors of both studies included employees of Martek Biosciences Corporation, a primary manufacturer of the algal DHA supplement. The study led by Dr. Quinn was conducted by the Alzheimer's Disease Cooperative Study and supported by the National Institute on Aging; the study led by Dr. Yurko-Mauro was supported by Martek Biosciences Corporation.