Consumption of omega-3 polyunsaturated fatty acid supplements has no measurable effect on cognition in older adults, according to U.K. researchers who sought to detect whether daily use of the supplements could prevent cognitive decline.
For their 2-year, blinded study, funded by U.K. health and nutrition agencies, a team of investigators led by Alan Dangour, Ph.D., of the London School of Hygiene & Tropical Medicine, randomly assigned 867 older adults in good cognitive health and who did not take fish-oil supplements to a daily dose of 200 mg eicosapentaenoic acid (EPA) plus 500 mg docosahexaenoic acid (DHA), or an olive-oil placebo.
The mean age of participants was 75 years; 55% were men, according to the study (doi: 10.3945/ajcn.2009.29121).
Though concentrations of EPA and DHA were significantly higher in blood samples from the treatment group, no decline in cognitive function was detected in either group. “After 2 years we can say definitively that there's no benefit,” Dr. Dangour said in an interview.
“We're disappointed, but we conducted the best possible study and certainly the largest to date.”
Standardized tests of memory and cognitive function and serum EPA and DHA levels were administered at baseline and after 24 months.
In the treatment arm, 376 subjects completed the study, compared with 368 in the control arm. Analysis was by intention to treat
The findings appear in stark contrast to those of a 2006 study of 899 similar-age subjects from a large cohort (Arch. Neurol. 2006;63:1545–50). In that study, people in the top quartile of plasma DHA levels saw a 47% reduction in the risk of developing all-cause dementia after 9 years.
But cohort studies are difficult to compare with randomized, controlled trials, Dr. Dangour pointed out, and “there are loads of other studies that say there's a benefit for people who eat more fish.”
The point of this study, specifically, was to detect a measurable benefit from a dietary change rather than the accumulated benefits of a lifelong habit.
Neither Dr. Dangour nor his coauthors declared any competing interests. Fish oil for the study was donated by Ocean Nutrition Canada Ltd.