Study: Fish Oil Supplements Did Not Improve Memory in Older Adults at Alzheimer's Risk Over Two Years

Fish oil supplements rich in omega-3 fatty acids did not provide measurable protection for memory and thinking skills in older adults at elevated risk of Alzheimer's disease. That is the conclusion of a two-year clinical trial by researchers at Keck Medicine of USC, the University of Southern California's medical system, published in the journal eBioMedicine.

Americans spend more than $1 billion a year on omega-3 supplements, hoping to preserve memory and brain health with age. The new results call that expectation into question.

How the trial worked

The study enrolled 365 adults aged 55 to 80 who rarely ate fish and were at higher risk of Alzheimer's. Some 47% carried the APOE4 gene variant, the strongest known genetic risk factor for late-onset Alzheimer's.

Participants were randomly assigned to take either a daily fish oil supplement providing 2,000 mg of docosahexaenoic acid (DHA), an omega-3 fatty acid especially important for the brain, or a placebo. The trial was double-blind, so neither participants nor researchers knew who received the active supplement.

What the researchers found

After six months, DHA levels in cerebrospinal fluid, the liquid surrounding the brain and spinal cord, had risen by an average of 17% in the supplement group, showing the nutrient was reaching the brain. Even so, this group did no better than the placebo group on memory and other cognitive tests. Brain imaging also showed the supplements did not prevent shrinkage of the hippocampus, a region central to forming memories.

Hussein Naji Yassine, director of the USC Center for Personalized Brain Health and lead investigator, said the results do not support fish oil supplements as a preventive measure against Alzheimer's.

The researchers stress that the findings do not mean omega-3s are unnecessary or that eating fish is without benefit. They are now studying how the brain absorbs and uses these nutrients, and suggest omega-3s may work better as part of a broader diet such as the Mediterranean diet. They are also working on medications that could help the brain make better use of them.

The team points to regular exercise, quality sleep and a balanced diet as the main tools for reducing risk, though these factors were not directly tested in the trial. The work was funded by the US National Institutes of Health and the Alzheimer's Drug Discovery Foundation.