Hussein Naji Yassine led a two-year brain study of 365 adults ages 55 to 80 that tested whether 2,000 mg of DHA could protect memory. The supplements raised DHA in cerebrospinal fluid, but the trial found no improvement in cognition or hippocampal shrinkage.
Published in eBioMedicine, the placebo-controlled and double-blinded trial studied adults who rarely ate fish, and 47% carried APOE4. The finding lands in a market where Americans spend more than $1 billion each year on fish oil supplements.
Hussein Naji Yassine and the trial design
The study began by measuring participants’ memory and thinking before they took either DHA or a placebo for two years. Each supplement contained 2,000 mg of docosahexaenoic acid, and all 365 participants were between 55 and 80 years old.
At six months, DHA levels in cerebrospinal fluid had increased by an average of 17%. That showed the supplement reached the brain, but the later assessments did not show better test performance or less hippocampal shrinkage.
eBioMedicine results and limits
Hussein Naji Yassine said, “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” and “While omega-3s play an important role in forming brain cell connections needed for cognition, our results do not support fish oil supplements as a preventive measure against Alzheimer's.”
The result narrows the claim around standalone fish oil pills: they can change a biological marker without changing the outcomes the trial measured. Earlier research had suggested omega-3s may work better as part of a Mediterranean-style eating pattern than as an isolated supplement, and this trial adds a direct test of the supplement approach.
USC Center for Personalized Brain Health
Yassine, who leads the USC Center for Personalized Brain Health, said the study does not support fish oil supplements as prevention against Alzheimer's. The next question is why DHA can reach the brain and still leave memory, cognition, and hippocampal shrinkage unchanged in older adults at increased risk for the disease.
