A two-year clinical trial led by researchers at Keck Medicine of the University of Southern California found no measurable cognitive benefit from daily fish oil supplements in older adults at elevated risk of Alzheimer's disease. Published in eBioMedicine, the study enrolled 365 adults ages 55 to 80 who rarely consumed fish. Nearly half, 47%, carried APOE4, a genetic variant associated with increased Alzheimer's risk. Participants were randomly assigned either 2,000 milligrams of DHA daily or a placebo. Neither participants nor researchers knew who received the active supplement during the trial.
DHA, an omega-3 fatty acid, helps maintain brain cell membranes and supports communication between neurons. After six months, its concentration in cerebrospinal fluid, which surrounds the brain and spinal cord, had increased by an average of 17% among supplement recipients. Nevertheless, after two years, this group showed no advantage over the placebo group on memory and other cognitive tests. Brain imaging likewise found no protection against shrinkage of the hippocampus, a structure central to memory formation. The results indicate that increasing DHA availability alone was insufficient to produce measurable benefits in this population.
The findings do not negate the importance of omega-3 fats or the health benefits of eating fish. Researchers are investigating whether dietary patterns, overall health, genetic risk, and age influence the brain's ability to absorb and use these nutrients. Their earlier research suggests omega-3s may be more beneficial within a broader dietary pattern than as isolated supplements. A Mediterranean-style diet has been associated with lower Alzheimer's risk. Rather than relying on fish oil alone, the team recommends regular physical activity, high-quality sleep, and a balanced diet to support long-term brain health.
