Millions of Americans take fish oil supplements in hopes of protecting their memory and keeping their brains healthy as they age. These products have become big business, with Americans spending more than $1 billion on supplements containing omega-3 fatty acids each year. These essential nutrients help establish and maintain the connections between brain cells that support memory, learning and other cognitive functions.
But a new study suggests that getting more omega-3 into the brain through supplements may not provide the protection many people expect.
Researchers at Keck Medicine of USC found that even when high doses of omega-3 reached the brain, they did not produce measurable improvements in memory, thinking skills, or protection against brain shrinkage.
The results, published in eBioMedicinecome from a two-year clinical trial involving older adults considered to be at increased risk of developing Alzheimer’s disease. Despite taking daily omega-3 supplements, participants showed no significant cognitive benefits compared to those who received a placebo.
“We all wish there was a silver bullet to prevent Alzheimer’s disease, but our results showed that fish oil supplements do not appear to protect brain health,” said Hussein Naji Yassine, MD, director of the Center for Personalized Brain Health at USC and principal investigator of the study. “Although omega-3 plays an important role in forming the connections between brain cells necessary for cognition, our results do not support fish oil supplements as a preventative measure against Alzheimer’s disease.”
Two-year study tests brain benefits of fish oil
To determine whether omega-3 supplements could protect the aging brain, researchers recruited 365 adults aged 55 to 80. All participants rarely ate fish, a major dietary source of omega-3 fatty acids, and were considered at high risk for Alzheimer’s disease.
Nearly half (47%) carried APOE4, a gene variant associated with a significantly higher risk of developing Alzheimer’s disease later in life. Although this variant does not necessarily mean someone will develop the disease, it is the strongest known genetic risk factor for late-onset Alzheimer’s disease.
Participants were randomly assigned to receive either a daily fish oil supplement or a placebo, an inactive treatment used for comparison. The supplements provided 2,000 mg of docosahexaenoic acid (DHA), an omega-3 fatty acid particularly important for the brain.
DHA is a major component of brain cell membranes, helping to maintain the structure and function of neurons. It also promotes communication between nerve cells, making it an important nutrient for normal brain activity.
The study was double-blind, meaning neither the participants nor the researchers knew who was receiving the active supplement during the trial. This approach helps reduce bias and makes it easier to determine whether the observed benefits are actually caused by the treatment.
Omega-3 levels increased, but memory did not improve
Before evaluating whether supplements improved brain health, researchers needed to answer a fundamental question: Do omega-3 fatty acids actually reach the brain?
To find out, they measured DHA concentrations in cerebrospinal fluid, the clear fluid that surrounds and cushions the brain and spinal cord. Examination of this fluid can provide information about substances entering and circulating in the central nervous system.
After six months, DHA levels in the spinal fluid had increased by an average of 17% in participants taking the supplements. This proved that omega-3 fatty acids were reaching their intended destination.
However, getting DHA into the central nervous system was only part of the goal. The more important question was whether these higher levels would translate into better brain health.
Researchers assessed participants’ memory and other cognitive abilities at the start of the trial and then again after two years. Despite the increase in DHA, those who took fish oil did not perform better on cognitive tests than participants receiving the placebo.
Brain imaging revealed equally disappointing results.
The supplements did not prevent the shrinkage of the hippocampus, a region deep in the brain that plays a central role in the formation and organization of memories. The hippocampus is particularly vulnerable to changes associated with aging and Alzheimer’s disease, making its size an important indicator that researchers use to study brain health.
Taken together, the results suggest that simply increasing DHA availability in the brain is not enough to produce measurable cognitive benefits in this group of older adults.
Why Fish Oil Supplements May Work Differently From Food
These unexpected findings raised a new question for researchers: If omega-3 can reach the brain, why don’t higher levels necessarily improve its functioning?
Yassine and his colleagues are currently studying how the brain absorbs, processes and uses these nutrients. Their previous research suggests that omega-3s may be more beneficial when consumed as part of a broader diet rather than taken in isolation as a supplement.
One possibility involves the Mediterranean-style diet, which emphasizes foods such as fish, vegetables, fruits, whole grains, legumes, nuts and olive oil. This eating pattern naturally provides omega-3 fatty acids along with other nutrients and has been linked to a lower risk of Alzheimer’s disease.
Researchers suspect that the combination of nutrients in a balanced diet, as well as an individual’s overall health, may influence how effectively omega-3 supports the brain.
“We are working to better understand how the brain processes omega-3s and whether factors, such as poor health, diet, genetic risk and age, can alter the brain’s ability to absorb and use omega-3s effectively,” Yassine said. “We are working to develop drugs that could help the brain better use these nutrients to preserve cognitive function.”
Understanding these differences could eventually help scientists identify why some people might respond better to omega-3s than others and whether new treatments might improve the brain’s ability to benefit from these essential fats.
It’s important to note that these results do not mean that omega-3 fatty acids are unnecessary or that eating fish offers no health benefits. Instead, they indicate that taking high-dose DHA supplements alone did not provide measurable protection against cognitive decline or hippocampal shrinkage in the study population.
Healthy habits remain key to preventing Alzheimer’s disease
Although the trial focuses specifically on fish oil supplements, the researchers emphasize that protecting brain health requires a much broader approach.
Rather than relying on a single supplement, they recommend maintaining healthy habits throughout life, including regular physical activity, getting enough, quality sleep, and eating a nutritious, balanced diet.
These behaviors support overall health and may help reduce factors associated with cognitive decline. Physical exercise, for example, promotes cardiovascular health and blood circulation, while sleep plays an important role in memory formation and normal brain maintenance.
“Staying healthy throughout life remains the most powerful tool we have to reduce the risk of Alzheimer’s disease, including regular exercise, quality sleep and a balanced diet,” Yassine said. “Living a healthy lifestyle is equivalent to the brain of regular car maintenance and high-quality oil changes. The brain is more likely to lose greater function if health problems in other parts of the body are not addressed, in the same way that car engines stop working if regular maintenance is ignored.”
Although these lifestyle factors were not directly tested in the trial, researchers believe they offer a more promising basis for long-term brain health than relying solely on fish oil supplements.
The findings also highlight an important distinction: A nutrient can be essential for healthy brain function without providing additional protection when consumed in high doses as a supplement. Understanding why this happens could open new avenues of research into Alzheimer’s disease prevention and the nutritional needs of the aging brain.
The research was supported by the National Institutes of Health, grant numbers RF1AG076124, R01AG055770, R01AG067063, R01AG054434, R21AG056518, P30AG066530, and R01AG054434 and by the Alzheimer’s Drug Discovery Foundation, grant number. GC-201711-2014197.
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