Two-Year DHA Trial Finds No Cognitive Benefit in Older Adults at Risk of Dementia

A new controlled trial has cast doubt on the idea that omega-3 supplements slow cognitive decline. Published last week in the Lancet group journal eBiomedicine, the two-year study examined whether DHA, a major omega-3 fatty acid, could improve cognition in adults ages 55 to 80 who had risk factors for dementia.

Researchers enrolled 365 participants whose diets were not rich in DHA. About 47% carried an APOE mutation, a major Alzheimer’s risk factor that scientists suspect may interfere with DHA activity in the brain. The participants were split into two groups, one taking a DHA supplement and the other taking a placebo.

After two years, the supplement group did show higher DHA levels in cerebrospinal fluid, measured through lumbar puncture. But the trial found no difference between the groups in cognitive performance or brain tissue volume. The result aligns with a 2020 review that also rejected claims that omega-3 supplements prevent cognitive decline.

Study co-lead Dr. Hussein Yassine of the University of Southern California told CNN that Mediterranean diets may be linked to better cognition, but that this does not prove supplements help. He said people in Mediterranean countries do not simply take pills, they eat fish, exercise, socialize, and live slower lives. He added, “If you eat fast food, are sedentary and stressed, raising DHA levels in the brain will not materially change your condition.”

The article explains that brain function depends on omega-3s, especially DHA and EPA, while ALA, found in foods such as chia seeds and walnuts, can be converted by the body only inefficiently. It also notes that the field still lacks a clear deficiency threshold, optimal dosing standards, and a reliable way to measure supplement effectiveness because omega-3 absorption varies widely between individuals. Current testing, including the Omega 3 index blood test, has limitations, and the lack of patent incentives makes large, definitive trials less likely. For now, the American Heart Association recommends two servings of fish a day for heart health, and the FDA has approved four omega-3 products to lower cholesterol, but whether that also helps cognition remains uncertain.