Short answer
Probably not much. A 2026 trial gave 365 older adults 2 grams of DHA a day or a placebo for 24 months and found no difference in memory tests or brain volume. For the heart, the big trials of standard fish oil in people without heart disease also found no drop in major events. One prescription omega-3 is the exception.
What the 2026 study found
The trial ran at the University of Southern California and was published in eBioMedicine in 2026. It enrolled 365 people aged 55 to 80 who did not have dementia, ate little DHA (under 200 mg a day), and had at least one dementia risk factor. About half (47%) carried APOE4, a gene linked to higher Alzheimer's risk. They took 2 grams of DHA a day or a placebo.
DHA did get into the nervous system: levels in spinal fluid rose. But over 24 months there was no difference between the groups in brain volumes or in cognitive performance.
The limits of that study
This was a phase 2a trial at a single university. Its main goal was to see whether DHA reaches the brain, and thinking tests were secondary measures. Dropout was 38%, mostly because of COVID-19, which makes small effects harder to detect. Nobody in it had dementia, and it lasted two years.
So it does not prove omega-3 is useless for every brain at every age. It shows that a high dose, given to the people thought most likely to benefit, did not move memory or brain size in 24 months.
What the big heart trials found
VITAL tested 1 gram a day of fish oil in 25,871 US adults for a median of 5.3 years. Major cardiovascular events were not significantly lower than with placebo. ASCEND found the same in 15,480 people with diabetes over 7.4 years. STRENGTH tested 4 grams a day in 13,078 high-risk patients on statins and was stopped early for a low chance of benefit.
The exception is REDUCE-IT. In 8,179 statin-treated patients with high triglycerides, 4 grams a day of icosapent ethyl, a prescription purified EPA, cut major events from 22.0% to 17.2%. That is a prescription drug in a specific group, not a store supplement.
The heart rhythm signal
A 2021 meta-analysis in Circulation pooled 7 trials and 81,210 patients. Omega-3 supplements were linked to a 25% higher relative risk of atrial fibrillation, an irregular heart rhythm. The risk looked larger in trials using more than 1 gram a day. In REDUCE-IT, 3.1% of the icosapent ethyl group were hospitalized for atrial fibrillation or flutter versus 2.1% on placebo.
In VITAL, at under 1 gram a day, the difference in atrial fibrillation was not statistically significant. If you take fish oil and have a heart rhythm problem, ask your doctor whether to continue.
Related questions
Should you stop taking fish oil?
That is a decision for you and your doctor. The trials above show no clear memory benefit and no drop in major heart events for most people without heart disease, and a small rise in atrial fibrillation risk at higher doses.
Is prescription omega-3 different from fish oil supplements?
Yes. REDUCE-IT tested icosapent ethyl, a highly purified EPA, at 4 grams a day in statin-treated patients with high triglycerides. Its result does not carry over to over-the-counter fish oil.
Did fish oil lower heart attacks in VITAL?
Heart attack, a secondary outcome, was lower (hazard ratio 0.72), but the main outcome of major cardiovascular events was not. Secondary results like this are treated as leads, not proof.
Read next
Sources
- Yassine et al., eBioMedicine: High-dose DHA in older adults at risk for dementia, randomized trial (2026)
- Manson et al., NEJM: VITAL, marine n-3 fatty acids and prevention of cardiovascular disease and cancer (2019)
- Bhatt et al., NEJM: REDUCE-IT, icosapent ethyl for hypertriglyceridemia (2019)
- Nicholls et al., JAMA: STRENGTH randomized clinical trial (2020)
- Gencer et al., Circulation: Marine omega-3 supplementation and atrial fibrillation, meta-analysis (2021)
Published 2026-10-04 · Last checked 2026-10-04
Educational content, not medical advice. Made for the United States.