Millions of Americans take fish oil supplements hoping to protect their memory as they age, spending more than $1 billion a year on omega-3 products. A new two-year clinical trial suggests that spending may not be buying what people expect.
Researchers at Keck Medicine of USC enrolled 365 adults aged 55 to 80 who rarely ate fish — a major dietary source of omega-3s — and were considered at elevated risk of Alzheimer's disease; nearly half carried APOE4, the strongest known genetic risk factor for late-onset Alzheimer's. Participants were randomly assigned to a daily supplement containing 2,000mg of DHA, an omega-3 fatty acid important for brain function, or a placebo, in a double-blind design.
The nutrient reached the brain — but didn't help
After six months, DHA levels in participants' cerebrospinal fluid had risen by an average of 17%, confirming the supplement was reaching the central nervous system. But after two years, those taking fish oil performed no better on memory and cognitive tests than those on placebo, and brain scans showed the supplements did not prevent shrinkage of the hippocampus, the brain region most central to memory and most vulnerable to Alzheimer's-related decline.
"We all wish there was a silver bullet for preventing Alzheimer's, but our findings showed that fish oil supplements do not appear to protect brain health," said Dr Hussein Naji Yassine, the study's lead investigator and director of the USC Center for Personalized Brain Health. The results, published in eBioMedicine, have left researchers investigating why raising DHA levels in the brain doesn't straightforwardly translate into better cognitive outcomes — with one theory being that omega-3s may do more good as part of a broader diet, such as a Mediterranean-style eating pattern, than taken alone as a pill.
"We're focused on better understanding how the brain processes omega-3s," Yassine said, "and whether factors such as poor health, dietary pattern, genetic risk and age may change the brain's ability to effectively absorb and use" them.