July 15, 2026
Do you take fish oil supplements in the hopes of boosting your brain health? You may want to save your money for some fresh seafood instead. A rigorous new trial found that fish oil supplements provided no cognitive benefits in older adults at increased risk of developing Alzheimer’s disease.
Earlier studies have shown that eating seafood at least twice a week lowers your risk of developing Alzheimer’s disease. Fatty fish such as salmon, tuna, anchovies, mackerel and trout are rich in “good” fats known as omega-3 fatty acids, which have been shown to fight inflammation and maintain structural integrity in aging brains. Some small studies suggested that taking supplements containing omega-3s like docosahexaenoic acid, or DHA, may help to stave off dementia.
This study, from researchers at the University of Southern California, was larger than most previous fish oil supplement brain studies. It found that high daily doses of fish oil boosted levels of omega-3s in the brain. Those higher levels, however, appeared to provide no boosts to memory or thinking skills or brain integrity in high-risk adults who took them over two years.
“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,” said Dr. Hussein Naji Yassine, the study’s lead author and director of the USC Center for Personalized Brain Health. “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.”
For the study, researchers enlisted 365 men and women, ranging in age from 55 to 80, who rarely ate fish. None had serious memory problems, though all had at least one dementia risk factor, such as obesity, high blood pressure or being physically inactive. Almost half carried the APOE-E4 gene variant, the strongest genetic risk factor for the disease.
The study was placebo-controlled and double-blinded, the gold standard of medical research. Participants were randomly assigned to receive either a daily fish oil supplement containing 2,000 milligrams of DHA or a lookalike placebo pill.
Within six months, the researchers documented increased levels of DHA in fluids surrounding the brains of those taking the supplements. The finding confirmed that the omega-3s had successfully entered the brain.
Higher omega-3 brain levels, however, did not translate to clinical benefit. Researchers tested participants’ memory and thinking abilities at the beginning of the study and again two years later. Study participants who took DHA supplements did not do any better on the tests than those who took a placebo. Brain scans also showed that the supplements did not prevent shrinkage of the hippocampus, a brain region critical for memory that is often used as a marker of brain aging and Alzheimer’s risk. Carrying the APOE-E4 gene variant did not affect the results. The findings were published in the journal eBioMedicine.
The researchers say that rather than taking a standalone supplement, omega-3s may be most effective when consumed as part of an overall nutrient-rich diet. Numerous studies have shown, for example, that a traditional Mediterranean-style diet, rich in fish, fruits, vegetables and whole grains, is associated with a decreased risk of developing Alzheimer’s disease. The Mediterranean diet provides a wide range of nutrients and heart-healthy fats, including omega-3s.
Fish and other seafood are rich in a variety of omega-3s in addition to DHA. Other good sources of omega-3s include walnuts, soybeans, chia seeds and flaxseed. The greatest benefits of a varied, nutrient-rich diet may accrue over time, well beyond the two-year length of this study, and in conjunction with other health-promoting lifestyle habits.
“Staying healthy throughout life remains the most powerful tool we have for reducing Alzheimer’s risk, including regular exercise, quality sleep and a balanced diet,” Dr. Yassine said.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, PhD, of The Fisher Center lab at The Rockefeller University.
Source: Hussein N. Yassine, Sara Ghasem Pour, Marlene Juarez, 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, June 18, 2026
