Scientists Say This Popular Cognitive Supplement May Be Ineffective

Fish oil has been a buzzy supplement for years, but a wave of recent research suggests that it doesn’t help as much as people once thought. While some past data have linked fish oil supplements to a lower risk of developing Alzheimer’s disease, a new study determines the opposite.

The study, published in eBioMedicine, implies that taking fish oil doesn’t do much of anything for cognitive health or Alzheimer’s disease risk.

Researchers recruited 365 adults aged 55 to 80 who rarely ate fish and who were considered at risk for developing Alzheimer’s disease. (About half of the participants carried an APOE4 gene, which is the strongest genetic risk factor for late-onset Alzheimer’s.) The participants were randomly assigned to either take fish oil supplements—specifically, ones that contained 2,000 mg of docosahexaenoic acid (DHA), an omega-3 fatty acid involved in brain function—or a placebo. While the researchers discovered that the supplements did increase levels of DHA in participants’ cerebrospinal fluid (by an average of 17% after six months), they didn’t affect outcomes.

The researchers tested the participants’ memory and cognitive abilities at the start of the study, and after two years of taking either the fish oil or a placebo. The participants who took DHA supplements did no better on the cognitive tests than those who took a placebo.

Meet the experts: Jessica Cording, M.S., R.D., registered dietitian and author of The Little Book of Game-Changers; Dung Trinh, M.D., internist at MemorialCare Medical Group and chief medical officer of Healthy Brain Clinic; Davide Cappon, Ph.D., director of neuropsychology at Tufts Medical Center; Hussein Naji Yassine, M.D., lead study author and director of the USC Center for Personalized Brain Health.

Brain scans also found that the supplements didn’t affect hippocampus shrinkage. (The hippocampus is a brain region that’s important for memory, and hippocampus shrinkage is used as a marker of brain aging and to determine Alzheimer’s risk.)

Overall, the findings suggest that there’s no value in taking fish oil supplements to lower your Alzheimer’s risk. Here’s what experts want you to keep in mind.

What is fish oil?

Fish oil is a dietary supplement that provides omega-3 fatty acids, according to the Mayo Clinic. Omega-3 fatty acids support a range of activities in the body, including cell growth and muscle activity.

Fish oil pills typically contain two types of omega-3 fatty acids: docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). However, you can get both DHA and EPA through your diet by eating fatty fish and shellfish, according to Jessica Cording, M.S., R.D., registered dietitian and author of The Little Book of Game-Changers.

Why doesn’t fish oil help with Alzheimer’s disease?

To be fair, the study focused on people who are predisposed to Alzheimer’s disease, so it’s tough to say for sure that the effect would be the same on the general population. But it adds to a larger body of mixed data on the role of fish oil in brain health.

One small clinical trial published in JAMA Network Open in 2024 found that people who took fish oil supplements didn’t see a significant reduction in cerebral white matter lesion accumulation—a core feature of Alzheimer’s disease—but suggested that the supplements might benefit people who carried an APOE4 gene in other ways.

A study published in April in the journal Cell Reports also found that fish oil supplements weren’t helpful when it came to healing from a traumatic brain injury—and might even interfere with the brain’s ability to heal itself. The researchers also discovered that EPA (again, a form of omega-3s) may support the buildup of the protein tau in the brain, which is a hallmark of Alzheimer’s disease.

What’s particularly interesting about the most recent study is that the researchers found that fish oil supplements do reach the brain (as measured by an increase in DHA levels in participants’ cerebrospinal fluid). They just don’t seem to affect Alzheimer’s risk. “This is an important distinction: Getting more DHA into the brain does not automatically mean that it will prevent memory loss or dementia, at least not when taken as a supplement by itself over this time period,” says Hussein Naji Yassine, M.D., lead study author and director of the USC Center for Personalized Brain Health.

The findings “suggest we still have more to learn about how the brain utilizes these nutrients and whether factors such as diet, genetics, overall health, or timing of intervention influence their effects,” says Davide Cappon, Ph.D., director of neuropsychology at Tufts Medical Center.

Dung Trinh, M.D., an internist at MemorialCare Medical Group and chief medical officer of Healthy Brain Clinic in Irvine, California, says the takeaway shouldn’t be that omega-3s are worthless. “It does not mean DHA has no role in brain biology,” he says.

Cording agrees. “This doesn’t say that fish oil doesn’t work for anybody, for anything,” she says. “It’s much more nuanced than that.”

“The problem may not be delivery,” Dr. Trinh says. The issue may be that Alzheimer’s risk is driven by several interacting pathways, including vascular disease, inflammation, insulin resistance, sleep disruption, inactivity, and depression, among other things. Fish oil alone simply can’t fix all of that.

Dr. Cappon agrees. “Brain aging and Alzheimer’s disease are complex processes,” he says. “A single supplement may not be enough to meaningfully influence that biology.”

What does fish oil do?

While the medical community is admittedly not as all-in with fish oil supplements as it once was, there’s some data to support the use of these supplements.

Older research linked eating a diet rich in omega-3s to a lowered risk of dying from heart disease, which caused people to turn to fish oil supplements for heart health. But the evidence is inconclusive: While some studies suggest that fish oil supplements can help prevent cardiovascular complications in certain groups, other studies don’t.

In terms of Alzheimer’s disease prevention, the data just isn’t there yet. “Fish oil is not a proven way to prevent Alzheimer’s disease,” Cappon says.

Should you take a fish oil supplement?

Omega-3s as a whole remain an important part of a healthy diet, Dr. Yassine says. “Foods rich in omega-3s, such as fatty fish, support overall heart and brain health and should be encouraged as part of a balanced dietary pattern,” he says. “But our findings do not support the idea that people should take high-dose DHA supplements alone to prevent dementia.”

If you’re concerned about your dementia risk, Dr. Yassine recommends focusing on eating a balanced diet that contains omega-3-rich foods, staying physically active, controlling blood pressure and cholesterol, sleeping well, and managing other dementia risk factors. “Future research should also focus on understanding how the brain uses DHA and whether certain groups of people may benefit more from targeted dietary or lifestyle interventions,” he says.

Cording still recommends that her patients use fish oil to fill gaps in their diet. “Fish oil can help someone … if they don’t like fish, or it doesn’t make sense for their lifestyle to prepare and eat fish,” she says. “But we are also still learning about what they are most supportive of, and for which populations.” It’s important to talk to a healthcare provider before putting yourself on any new supplement, including fish oil, Cording says.

Because brain health is complicated, Cappon says it can require a multi-pronged approach to keep your brain in good shape. “Brain health is usually the result of many small factors working together rather than a single intervention,” he says.

Cording also stresses this: “You can’t take a supplement and expect it to reverse a lifetime of other health factors that may have been contributing to a health issue.”