By Lew Kizer — 2026-10-24 — Health & Nutrition
The short answer
A randomized, double-blind trial from the University of Southern California, published in eBioMedicine in October 2026, gave 365 adults aged 55 to 80 at higher Alzheimer's risk either 2,000 mg of DHA daily or placebo for two years. DHA in spinal fluid rose 17% at six months, but memory and thinking scores and hippocampus shrinkage were no better than placebo.
Key facts
- 365 adults aged 55 to 80 who rarely ate fish; about 47% carried APOE4.
- Daily dose: 2,000 mg DHA vs placebo, for two years.
- Spinal-fluid DHA rose 17% at six months, showing it reached the brain.
- No improvement in memory and thinking tests or hippocampus shrinkage.
- Funded by the National Institutes of Health and the Alzheimer's Drug Discovery Foundation.
KINGSPORT, Tenn., Oct. 24, 2026 — Fish oil is one of the most popular supplements in America, often taken for the brain. A carefully designed two-year trial found it did not protect memory in older adults at risk for Alzheimer's.
This article reports research news and is not medical advice. Talk with your clinician before changing your diet, supplements or medicines.
The trial
| Detail | Value |
|---|---|
| Participants | 365 adults aged 55 to 80 |
| Risk | Rarely ate fish; about 47% carried APOE4 |
| Dose | 2,000 mg DHA a day or placebo |
| Length | Two years |
| Brain DHA | Up 17% at six months |
| Memory and thinking | No better than placebo |
“our results do not support fish oil supplements as a preventive measure against Alzheimer's.” — Hussein N. Yassine, MD, Keck Medicine of USC
Pills versus plates
The trial tested high-dose supplements in a specific group, not fish as food. The researchers suspect diet context, genetics and age may affect how the brain uses omega-3s, but that has not been tested. The NIH says some research links eating fish with lower dementia risk and that more study is needed. Our guide to fish versus fish oil walks through the evidence.
“Most meal preps take fifteen minutes. Ours takes eighteen hours.” — Lew Kizer, Founder, SmashMeals
Commentary, not medical advice
The SmashMeals perspective
We get asked a lot about supplements, and our honest answer is that a pill rarely does what a plate does. This trial was well run, the fish oil got where it was supposed to go, and it still did not move memory. The research on eating fish as part of a whole diet is a different and more encouraging story. Real food first.
Frequently asked questions
Does fish oil prevent Alzheimer's?
In a two-year trial of 365 at-risk older adults, 2,000 mg of DHA daily did not improve memory or slow hippocampus shrinkage compared with placebo. The lead researcher said the results do not support fish oil as a preventive measure.
Should I stop taking fish oil?
Talk with your clinician. Fish oil lowers triglycerides and may be prescribed for other reasons. High doses can interact with blood thinners.
Is eating fish still good for the brain?
Some research links eating fish as part of a healthy diet with lower dementia risk, though it is not proven. The American Heart Association suggests one to two seafood servings a week.
Sources and credits
Follow the original sources for context and verification. A reference is not an endorsement of SmashMeals.
- Millions take fish oil for brain health. A two-year study found no benefit (opens in a new tab)
ScienceDaily (Keck Medicine of USC)
Why it matters: Summary of the trial and quotes.
- CNS target engagement of high-dose DHA supplementation in older adults at risk for dementia (DOI 10.1016/j.ebiom.2026.106316) (opens in a new tab)
eBioMedicine
Why it matters: The peer-reviewed trial.
- Omega-3 fatty acids: fact sheet for consumers (opens in a new tab)
NIH Office of Dietary Supplements
Why it matters: Food sources, safety limits and what research shows.