# Fish Oil Supplements Show No Brain Benefit in Two-Year USC Study

> A Keck Medicine of USC clinical trial found that fish oil supplements offered no measurable improvements for memory or cognitive function in at-risk adults, despite omega-3s reaching the brain.

By PrimaryBrief newsroom · Published 2026-10-26T09:02:28.582638Z
Canonical: https://primarybrief.com/article/fish-oil-supplements-show-no-brain-benefit-in-two-year-usc-study-54a76fd0

A two-year clinical trial conducted by Keck Medicine of USC found that daily fish oil supplements did not provide measurable benefits for memory, cognitive function, or protection against brain shrinkage associated with Alzheimer's disease in at-risk adults [1][18][19]. These findings persist even though researchers confirmed the omega-3s successfully reached participants' brains [1][16][18].

This research challenges a widely held belief among consumers that fish oil supplements can prevent cognitive decline or enhance brain health. Americans spend over $1 billion annually on these supplements, often with the expectation of such benefits, making the study's conclusions relevant for public health decisions [15][18].

## What the records show

The study, published in *eBioMedicine*, was a placebo-controlled, double-blinded trial involving 365 adults aged 55 to 80 [14][15][18]. Participants were considered at elevated risk for Alzheimer's disease, with nearly half, 47%, carrying the APOE4 gene variant, a significant genetic risk factor for late-onset Alzheimer's [15][16][18]. Researchers enrolled individuals who rarely consumed fish [15][18].

Participants were randomly assigned to receive either 2,000 milligrams of docosahexaenoic acid (DHA), a key omega-3, or a placebo daily [15][18]. A critical aspect of the study design was verifying if the omega-3s reached the brain [14][16]. Researchers measured DHA levels in cerebrospinal fluid, the liquid surrounding the brain and spinal cord, and observed an average 17% increase in DHA concentrations in the supplement group's brains after six months [15][16][19]. Despite this confirmed delivery, after two years, memory and cognitive function test scores were no different between the supplement and placebo groups [15][19]. The study also found no difference in hippocampal shrinkage, an area of the brain vital for memory and affected by Alzheimer's [15][18].

## The timeline

The clinical trial spanned two years [1][18]. Researchers assessed DHA levels in cerebrospinal fluid at the six-month mark to confirm the supplement's entry into the central nervous system [15][19]. Memory and cognitive abilities were tested at the start of the study and again after two years [18].

## What changed and for whom

For consumers and medical professionals, these findings suggest that isolated fish oil supplements may not be an effective strategy for protecting memory and cognitive function, particularly against Alzheimer's-related decline [14][18]. The study's lead investigator, Dr. Hussein Naji Yassine, stated, "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" [18]. This information could prompt individuals to reassess their supplement choices and prioritize broader healthy lifestyle practices [14][18].

## What the subject has said publicly

Dr. Hussein Naji Yassine, who is the director of the USC Center for Personalized Brain Health and the lead investigator of the study, publicly addressed the results [18]. He commented, "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" [18]. Dr. Yassine further emphasized that overall healthy living, encompassing regular exercise, quality sleep, and a balanced diet, remains the most potent tool for reducing Alzheimer's risk [18].

## What we could not confirm

We could not confirm the specific funding sources for this clinical trial. We also could not confirm the precise definitions or parameters for what constitutes a "balanced diet" or "quality sleep" as referenced in Dr. Yassine's advice [18].

## Evidence cited
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