A two-year clinical trial led by researchers at Keck Medicine of the University of Southern California found no measurable cognitive benefit from daily high-dose fish oil supplements. Published in eBioMedicine, the study enrolled 365 adults aged 55 to 80 who rarely consumed fish and were considered at elevated risk of Alzheimer's disease. Participants were randomly assigned either 2,000 milligrams of docosahexaenoic acid (DHA) daily or an inactive placebo. The trial was double-blind: neither participants nor researchers knew which treatment individuals received.
DHA, an omega-3 fatty acid, helps maintain brain cell membranes and supports communication between nerve cells. After six months, participants receiving supplements showed an average 17% increase in DHA concentrations in their cerebrospinal fluid, which surrounds the brain and spinal cord. Yet this evidence that the nutrient was reaching the central nervous system did not translate into better performance on memory and thinking tests after two years. Brain imaging also showed no protection against shrinkage of the hippocampus, a region central to memory formation.
The findings do not imply that omega-3s are dispensable or that fish lacks health benefits; they indicate that increasing DHA through supplements alone provided no measurable protection in this population. Lead investigator Hussein Naji Yassine and colleagues are examining how the brain absorbs and uses omega-3s, including whether age, genetic risk, overall health and dietary patterns influence that process. Earlier research suggests these fats may be more beneficial within a broader dietary pattern than in isolation. The researchers recommend regular physical activity, sufficient high-quality sleep and a balanced diet rather than reliance on supplements, although those lifestyle measures were not tested in this trial.
