Something Fishy about the DHA-Alzheimer's Link

Is fish oil really able to reduce the risk of Alzheimer's dementia?

Despite the results of earlier studies that suggest the possibility of a link between consumption of the omega-3 fatty acid docosahexaenoic acid (DHA) and reduced risk of developing Alzheimer’s disease (AD), a study to be published tomorrow in JAMAand presented by Joseph F. Quinn, MD, Oregon Health and Science University, Portland VA Medical Center, Portland, OR, at a JAMA media briefing at the National Press Club—found that patients with mild to moderate AD who received supplementation with DHA did not experience a reduced rate of cognitive and functional decline, when compared to patients who received placebo.

"Several studies have found that consumption of fish, the primary dietary source of omega-3 fatty acids, is associated with a reduced risk of cognitive decline or dementia,” wrote the authors. “Some studies have found that consumption of DHA, but not other omega-3 fatty acids, is associated with a reduced risk of Alzheimer disease." But these observational studies didn’t control who did and who did not receive DHA.

For the current study, 402 patients with mild to moderate Alzheimer’s disease were observed at 51 US research sites between November 2007 and May 2009. Each was randomly assigned to DHA 2g per day or placebo for 18 months, with cognitive and functional abilities assessed using the Alzheimer’s Disease Assessment Scale (ADAS-cog) and the Clinical Dementia Rating (CDR) sum of boxes. In a subsample of participants, volumetric MRI was used to determine rate of brain atrophy.

After reviewing data on 171 patients in the DHA group and 124 in the placebo group who finished the study, the investigators found no beneficial effect with DHA supplementation on rate of change on ADAS-cog score. Over the 18 months, the rate of average change in ADAS-cog score was 8.27 points for the placebo group, compared to 7.98 for the DHA group. On the CDR sum of boxes, the rate of points change was 2.93 for the placebo group and 2.87 for the DHA group. Analysis of MRIs in the subsample who received them showed no effect of DHA on total brain volume change.

"In summary, these results indicate that DHA supplementation is not useful for the population of individuals with mild to moderate Alzheimer disease," wrote the authors, adding that “because part of the rationale for the trial was epidemiological evidence that DHA use before disease onset modifies the risk of Alzheimer disease, it remains possible that an intervention with DHA might be more effective if initiated earlier in the course of the disease in patients who do not have overt dementia.”

Kristine Yaffe, MD, University of California, San Francisco and Veterans Affairs Medical Center, San Francisco, in an editorial that accompanied the JAMAarticle, wrote "This trial adds to a growing literature that treatment with DHA does not improve symptoms of AD. Although several observational studies reported that diets rich in fish or supplements with omega-3 fatty acids were associated with reduced risk of developing AD, most randomized clinical trials for treatment of AD or mild cognitive impairment or in healthy elderly individuals have not found a beneficial effect."

Are the results of this study enough for you tell your patients to forget about taking fish oil/omega-3/DHA supplements? Are they/could they be helpful in fighting off other diseases and conditions?