Millions of people swallow fish oil capsules hoping they’re doing something beneficial for their brains, but a new study shows the connection is questionable.
DHA reached the brain—but didn’t protect it
Scientists at the University of Southern California’s Keck School of Medicine examined whether high doses of DHA, an omega-3 fatty acid, could slow cognitive decline in older adults at risk for Alzheimer’s. Their findings revealed the supplements increased DHA levels in the brain but did not improve memory, thinking skills, or brain structure over two years.
“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 Hussein Naji Yassine, the study’s lead author and director of the USC Center for Personalized Brain Health. “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 preventative measure against Alzheimer’s.”
The trial involved 365 adults aged 55 to 80 who rarely ate fish, a natural source of omega-3s. Nearly half carried APOE4, the strongest genetic risk factor for late-onset Alzheimer’s. Participants were randomly assigned to take either a 2,000-milligram DHA supplement or a placebo daily. Neither the participants nor the researchers assessing them knew who was taking which.
After six months, cerebrospinal fluid tests confirmed DHA levels had risen by 17% in those taking the supplement. When memory and cognitive function were tested two years later, no difference emerged between the groups. Brain scans also revealed no protection against hippocampal shrinkage, a key marker of Alzheimer’s risk.
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Why supplements fell short
The results challenge one common explanation for the disappointing results of earlier fish oil studies: perhaps the omega-3s were simply not reaching the brain. In this trial, they clearly did. Yet, there was still no measurable cognitive benefit.
DHA is a critical component of brain cell membranes and plays a role in the connections brain cells use to communicate. The unanswered question is why increasing DHA levels through a high-dose supplement did not produce better results.
The findings do not eliminate other potential benefits of fish oil. However, those taking them solely to protect memory should consider the results when discussing options with a healthcare provider.
One question remains: if DHA is essential for brain function, why didn’t higher levels lead to better outcomes? Researchers will investigate how aging and genetic factors might change the way the brain uses omega-3s—and whether food sources offer advantages over pills.
The rising costs of certain medications highlight broader concerns about healthcare expenses, though this study focuses on a different aspect of prevention.
