Study: Fish Oil Supplements Don't Boost Brain Health in Older Adults

Americans spend over $1 billion annually on fish oil supplements, driven by claims that omega-3 fatty acids support brain health. However, new research from Keck Medicine of USC, published in eBioMedicine, challenges this expectation.

The two-year, placebo-controlled, double-blinded trial involved 365 adults aged 55 to 80 who rarely ate fish. All participants were considered at elevated risk for Alzheimer's disease, with nearly half (47%) carrying the APOE4 gene, the strongest genetic risk factor for late-onset Alzheimer's.

Participants were randomly assigned to receive either a daily fish oil supplement containing 2,000 mg of DHA (an omega-3 fatty acid) or a placebo. After six months, DHA levels in cerebrospinal fluid increased by an average of 17%, confirming that the nutrient reached the brain.

Despite this, the supplements did not translate into cognitive benefits. Researchers assessed memory and thinking at the start and after two years: those taking DHA performed no better on cognitive tests than the placebo group. Brain imaging also showed no slowing of hippocampal shrinkage, a marker of brain aging and Alzheimer's risk.

Lead investigator Dr. Hussein Naji Yassine noted that omega-3s may be more effective when consumed as part of a Mediterranean-style diet rather than as standalone supplements. The team is now investigating why the brain might not effectively use omega-3s, considering factors like poor health, diet, genetics, and age.

While lifestyle factors were not directly studied, researchers emphasize that maintaining overall health—regular exercise, quality sleep, and a balanced diet—remains the most powerful tool for reducing Alzheimer's risk. "Staying healthy throughout life is the brain's equivalent of getting regular car maintenance," said Yassine.