A high-dose DHA supplement raised DHA levels in the spinal fluid of older adults at risk for dementia. Over two years, though, it did not change memory and thinking tests or brain volume compared with placebo.[1]
Many people take fish oil hoping it will protect their memory as they age. It is a reasonable hope, and one of the most common supplement questions in midlife. Here is what this trial tested, and what it found.
What the trial did
The study enrolled 365 adults aged 55 to 80 (average age 66) who did not have dementia but had at least one risk factor for it. All ate little DHA through food, under 200 mg a day. About 47% carried the APOE ε4 gene variant, which raises Alzheimer’s risk. Half were randomly assigned to 2 grams of DHA a day, an omega-3 fatty acid, and half to a placebo. The trial ran for 24 months.
What it found
The main measure was the ratio of DHA to arachidonic acid (AA, another fatty acid) in cerebrospinal fluid, the fluid that surrounds the brain and spinal cord. At six months, the ratio was 0.17 in the DHA group and -0.02 in the placebo group, a difference of 0.19. The difference was clear and did not depend on APOE ε4 status.
A higher ratio tells us the supplement reached the fluid around the brain. It does not tell us the brain worked better. That question was answered by the two-year measures, and there the authors reported no differences between groups in brain volumes or cognitive performance.
Why the design matters
Randomization and a placebo group let researchers separate a supplement’s effect from everything else that differs between people who take it and people who don’t. Double-blinding keeps participants and researchers from shaping the results through expectation. That is why a null result from a trial like this deserves to be taken seriously, as far as one trial goes.
What this does not tell you
- This is one phase IIa trial, an early-stage design. One study should be confirmed before it changes practice.
- About 38% of participants dropped out, mainly because of COVID-19, which limits how firmly the two-year results can be read.
- Participants were selected for dementia risk and low DHA intake. Findings may not apply to people with different diets or health profiles.
- Follow-up was 24 months. Effects that take longer to appear would not show up here.
- The published summary says there were no differences in brain volumes or cognitive performance, but it does not give the specific tests or measurements, so this article does not either.
- This trial does not show that DHA prevents or treats dementia or memory loss. It also does not show that eating fish is useless.
What to do with it
The authors conclude that the supplement did what it was meant to do biochemically, but that this did not translate into cognition or brain-structure differences over two years. They suggest future research focus on how the brain handles DHA rather than on more supplementation trials.
Fish is one common food source of omega-3s. If you are considering a fish oil supplement, talk with your clinician first, especially if you take blood thinners or have a bleeding risk.
This article is educational and is not medical advice. Talk with your clinician about your own health decisions.
References
[1] Yassine HN, et al. CNS target engagement of high-dose DHA supplementation in older adults at risk for dementia: a randomised, double-blind, placebo-controlled trial. eBioMedicine. 2026;129:106316. DOI: 10.1016/j.ebiom.2026.106316. Finding as used: in 365 randomised adults aged 55 to 80 at risk for dementia, 2 g/day DHA: the 6-month CSF DHA/AA ratio was 0.17 (95% CI 0.15 to 0.18) versus -0.02 (95% CI -0.04 to -0.0004) with placebo; difference 0.19 (95% CI 0.16 to 0.21), p<0.0001, independent of APOE ε4 status. At 24 months there were no treatment differences in brain volumes or cognitive performance. Dropout was 38%, mainly due to COVID-19. ↑︎
Kurt Greiner
Kurt is a digital strategist and IT professional blending emerging technology with practical application, exploring how individuals can leverage modern tools to navigate the second half of life with purpose.
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