Fish oil supplements show no brain benefit in Alzheimer’s risk trial
A two-year USC-led trial found high-dose DHA reached the brain but did not improve cognition or slow Alzheimer’s-linked brain changes.
By Tom Brennan · Health & Medicine Correspondent
3 min read
A large clinical trial led by USC researchers found that high-dose omega-3 fish oil supplements did not improve memory or slow brain changes tied to Alzheimer’s disease in older adults at elevated risk. The findings matter because many Americans buy fish oil pills for brain health, while the trial found no measurable protection despite evidence that the supplement’s main omega-3 reached the brain.
Keck Medicine of USC said the randomized, double-blind, placebo-controlled study was published in eBioMedicine. According to USC Health Sciences, Americans spend more than $1 billion a year on fish oil supplements, often based on claims that omega-3 fatty acids support the brain.
The trial enrolled 365 adults ages 55 to 80 who rarely ate fish, which USC identified as a major dietary source of omega-3 fatty acids. Researchers classified the participants as having increased Alzheimer’s risk, and 47% carried APOE4, described by USC as the strongest known genetic risk factor for late-onset Alzheimer’s disease.
Participants received either a daily placebo or a fish oil supplement containing 2,000 milligrams of docosahexaenoic acid, or DHA, an omega-3 fatty acid linked to brain function, according to USC. Researchers then tracked whether DHA entered the central nervous system and whether it affected thinking, memory or brain structure.
DHA reached the brain, but outcomes did not change
USC said the investigators measured DHA in cerebrospinal fluid, the fluid around the brain and spinal cord. After six months, DHA levels rose by an average of 17%, which the researchers took as evidence that the nutrient had reached the brain.
That biological effect did not produce a clinical benefit, according to the study team. After two years, participants taking DHA did no better on memory and cognition tests than those taking placebo, USC said.
Brain scans also did not show protection against shrinkage of the hippocampus, according to USC. The hippocampus is a memory-related brain region that researchers use as a marker of brain aging and Alzheimer’s risk.
Hussein Naji Yassine, director of the USC Center for Personalized Brain Health and the study’s lead investigator, said the results do not support fish oil supplements as a way to prevent Alzheimer’s. He said omega-3s help form brain-cell connections needed for cognition, but the trial did not show that supplement use preserved brain health.
Researchers look beyond pills
USC said the findings have led researchers to ask why omega-3s can enter the brain without producing detectable gains in cognition or brain structure. Yassine and colleagues suspect, based on earlier research, that omega-3s may work differently when consumed through a broader Mediterranean-style diet rather than as a standalone pill.
According to USC, the Mediterranean diet naturally includes omega-3s and has been linked in prior research to lower Alzheimer’s risk. Yassine said his team is studying whether health status, diet, genetic risk and age affect how the brain absorbs and uses omega-3s, and is working on medications that may help the brain use such nutrients to preserve cognition.
The researchers did not directly test lifestyle factors in this trial, USC said. Yassine said regular exercise, good sleep and a balanced diet remain central tools for reducing Alzheimer’s risk and supporting brain function over a lifetime.
This story draws on original reporting from ScienceDaily.