DHA doesn't slow decline in mild to moderate Alzheimer's

DHA supplements did not affect rates of cognitive and functional decline compared with placebo in adults who had mild to moderate Alzheimer's disease, according to a new study.

Researchers from the Alzheimer's Disease Cooperative Study, a consortium funded by the National Institute on Aging, conducted a randomized, double-blind, placebo-controlled trial at 51 U.S. clinical research centers to determine whether DHA supplements would slow decline in patients with Alzheimer's disease. The study was conducted between November 2007 and May 2009. Eligible patients had a Mini-Mental State Examination (MMSE) score between 14 and 26, were medically stable, were currently consuming 200 mg of DHA per day or less, and were not taking supplements of DHA or omega-3 fatty acids. The study had two co-primary outcome measures over 18 months: rate of change on both the cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-cog) and the Clinical Dementia Rating (CDR) sum of boxes. Brain atrophy rate was also measured by volumetric MRI in a subpopulation of 102 patients, 53 in the DHA group and 49 in the placebo group. The study results were published in the Nov. 3 Journal of the American Medical Association.

Four hundred two patients were randomly assigned to receive algal DHA, 2 g/d, or identical-appearing placebo. Two hundred ninety-five patients completed the trial while still taking study medication, 171 in the DHA group and 124 in the placebo group. ADAS-cog score was not affected by DHA supplementation (mean increase over 18 months, 7.98 points [95% CI, 2.44 to 3.30 points] in the DHA group vs. 8.27 points [95% CI, 6.72 to 9.82 points] in the placebo group; P=0.41), nor was the CDR sum of boxes score (mean increase over 18 months, 2.87 points [95% CI, 2.44 to 3.30 points] vs. 2.93 points [95% CI, 2.44 to 3.42]; P=0.68). In patients who underwent volumetric MRI, brain atrophy did not differ by study group.

The authors concluded that cognitive and functional decline did not slow in patients with mild to moderate Alzheimer's disease who took DHA supplements. The study had a high dropout rate (28% in the DHA group and 24% in the placebo group), which the authors attributed to participants' belief that the study drug was not helping them, suggesting that future studies try to “temper the expectations of participants or run the risk of a dropout rate that may limit the ability to generalize study results,” they wrote.

Future studies should also test whether DHA supplementation could have more of an effect if offered earlier, for example in patients with mild cognitive impairment, the authors said. Finally, they noted that in an exploratory analysis of their data, a benefit was seen on the ADAS-cog and MMSE in DHA participants who were APOE ε4-negative, but cautioned that these results would need to be confirmed in a randomized, controlled trial.