New Study Questions Brain Health Benefits of Omega-3 Fish Oil Supplements

High-dose fish oil supplements increased omega-3 levels in the brain but did not improve memory, thinking abilities, or protect against brain shrinkage associated with Alzheimer's disease, according to a two-year clinical trial published in eBioMedicine.

Researchers from Keck Medicine of USC enrolled 365 adults aged 55 to 80 who rarely ate fish and were considered at increased risk of Alzheimer's disease. Nearly half of the participants carried the APOE4 gene, the strongest known genetic risk factor for late-onset Alzheimer's. Participants were randomly assigned to receive either a daily supplement containing 2,000 mg of docosahexaenoic acid (DHA), an omega-3 fatty acid, or a placebo.

To determine whether the supplement reached the brain, researchers measured DHA levels in cerebrospinal fluid. After six months, DHA levels had increased by an average of 17%, confirming that the omega-3 fatty acid successfully crossed into the brain.

Despite this increase, participants taking DHA showed no significant improvements in memory or cognitive performance compared with those receiving the placebo. Brain scans also revealed no reduction in shrinkage of the hippocampus, a region essential for memory that commonly deteriorates during aging and Alzheimer's disease.

The researchers believe the findings suggest that simply increasing brain DHA levels through supplements may not be enough to preserve cognitive function. They propose that omega-3s may be more beneficial when consumed as part of an overall healthy dietary pattern, such as the Mediterranean diet, rather than as isolated supplements.

While the study found no evidence that fish oil supplements prevent Alzheimer's-related brain changes, the researchers emphasize that regular exercise, quality sleep, a balanced diet, and maintaining overall health remain the most effective evidence-based strategies for supporting long-term brain health.

REFERENCE: Hussein N. Yassine, Sara Ghasem Pour, Marlene Juarez, Isabella C. Arrelanas, Nada Ali, Dante Dikeman, Ashley Sanchez, Jackson Park, Bilal Kerman, Marlon V. Duro, Isaac Asante, Stan Louie, Naoko Kono, Lina M. D\'Orazio, Helena Chui, Wendy J. Mack, Michael G. Harrington, Meredith N. Braskie, Lon S. Schneider. CNS target engagement of high-dose DHA supplementation in older adults at risk for dementia: a randomised, double-blind, placebo-controlled trial. eBioMedicine, 2026; 106316 DOI: 10.1016/j.ebiom.2026.106316