Can omega-3 supplements prevent or delay Alzheimer’s disease in people at risk? Let’s see what recent research says.
DHA, a key fatty acid for the brain
Docosahexaenoic acid (DHA) is a long-chain omega-3 fatty acid, present in fish and seafood, certain algae, and flax-fed eggs. The body can also synthesize a little from alpha-linolenic acid (walnuts, flax, rapeseed). Omega-3s promote brain functions, in particular because they promote the fluidity of cell membranes.
An encouraging lead among carriers of the APOE4 gene
Being a carrier of the APOE4 gene is one of the risk factors the most important causes of developing Alzheimer’s disease. This allele is present in 15 to 25% of the general population, but in approximately 40% of Alzheimer’s patients.
Promising results in animals
In 2017, a review published in JAMA Neurology by a team from the University of Southern California (USC) took stock of the role of DHA in Alzheimer’s disease. In animals, mice and rats receiving sufficient DHA for at least 10% of their lifespan did not develop signs of the disease in the brain (amyloid plaques). In mice carrying the APOE4 gene, high doses of DHA administered from a very young age even prevented the appearance of these characteristics.
An association observed in humans
In humans, numerous observational studies show an association between high DHA or fish consumption and a lower risk of Alzheimer’s disease, better cognitive outcomes and better preserved brain volumes. A meta-analysis of 21 observational studies showed that consuming fish once a week is associated with a significantly lower risk of dementia, compared to no consumption.
According to the authors of the 2017 reviewthe benefit of DHA supplementation seemed particularly clear in people at risk, carriers of the APOE4 allele, but who have not yet developed dementia. A study that autopsied the brains of carriers of the APOE4 allele after their death showed that those who consumed seafood once a week presented fewer neuropathological changes linked to Alzheimer’s than others.
“Epidemiological studies show an association between high intakes of omega-3, particularly DHA, and a reduced risk of Alzheimer’s disease.explained Dr. Yassine and his co-authors. But clinical trials have led to mixed and inconclusive results. »
Clinical trials with contrasting results
Results from 14 clinical trials show that health supplementsfish oil have no effectiveness in patients already diagnosed with Alzheimer’s: it is not possible to reverse neuronal degeneration with omega-3. In healthy people, the results are more mixed: some trials report benefits, others not.
Read: How Omega-3s Support Brain Function
New results in 2026
More recently, the same USC team, led by Dr. Yassine, conducted a clinical trial, the results of which appeared in June 2026 in the journal eBioMedicine. The study followed for two years 365 people aged 55 to 80, who consumed little fish and were considered at risk of Alzheimer’s disease. Nearly half (47%) of participants carried the APOE4 allele. They received either a placebo or a daily supplement of 2,000 mg of DHA.
First observation: DHA reaches its target. The researchers measured an average increase of 17% in DHA levels in the cerebrospinal fluid after six months of supplementation, confirming that omega-3 was reaching the brain.
Little effect on memory
But on memory and cognitive functionstested at the start of the study and then two years later, the participants supplemented with DHA did not do better than those in the placebo group. Brain MRIs also showed no difference in shrinkage of the hippocampus, a key region of memory and a classic marker of brain aging and Alzheimer’s risk.
“We all wish there was a silver bullet to prevent Alzheimer’s, but our results show that fish oil supplements do not appear to protect brain health”summarizes Dr Yassine in a university press release. “While omega-3s play an important role in forming the brain connections necessary for cognition, our results do not support recommending fish oil supplements as a preventive measure against Alzheimer’s. »
The Mediterranean diet, stronger protection than the supplement alone
For researchers, omega-3 works best when integrated into a Mediterranean diet, naturally rich in omega-3 and already associated with a reduced risk of Alzheimer’s disease, rather than as an isolated supplement. This seems confirmed by a 2015 meta-analysis, focusing on dietary fish consumption rather than supplementation. It shows that the biggest consumers of fish have a 36% reduced risk of Alzheimer’s disease. compared to the lowest consumerswith protection that increases over long follow-up: up to 47% less risk for follow-up of more than 5 years. Each additional 100g serving of fish per week is associated with an 11% reduction in risk.
Read: After 65, we think better when we have a lot of omega-3
“Staying healthy throughout life remains the most powerful tool we have to reduce the risk of Alzheimer’s, through regular exercise, quality sleep and a balanced diet”concludes Dr. Yassine.
