People taking fish-oil supplements in an effort to shield their brain from Alzheimer’s disease (AD) might be better off investing that money in their diet, with a two-year study finding that omega-3 pills offer no protection from cognitive decline.
In a new study from the University of Southern California (USC), researchers set out to see whether fish-oil supplements could first reach their target – the brain – and, once there, boost memory and cognitive abilities.
They conducted a two-year, placebo-controlled, double-blinded study of 365 older adults aged 55 to 80, who had a higher risk of developing AD and rarely ate fish – a natural source of omega-3 fatty acids. Nearly half of the study population – 47% – carried one APOE4 gene, which holds the highest genetic risk of late-onset AD.
Those assigned to take an active dose were prescribed 2,000 mg of docosahexaenoic acid (DHA), a key omega-3 for brain health, to be taken regularly throughout this lengthy study.
The good news was that the omega-3 in the supplements did in fact reach the target. Assessing cerebrospinal fluid around the brain, the scientists found that those who had taken the fish oil pills had an average 17% increase in DHA levels after six months, compared with the placebo group. And there’s strong evidence that this polyunsaturated fatty acid (PUFA) is beneficial for brain health.
However, when researchers tested participants’ memory and cognition two years later, the higher doses of omega-3s had no impact on areas closely tied to AD, with no difference in brain cell loss in key areas compared with the placebo group.
“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,” says lead researcher Hussein Naji Yassine, MD, 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.”
Those taking supplements did not perform any better in cognition or memory tests, and brain scans showed that omega-3 pills had no impact on loss of brain tissue in the hippocampus, which is closely tied to memory and is used to measure brain aging and AD risk.
Earlier studies have also revealed that fish-oil supplements aren’t effective in protecting the cardiovascular system and, despite a 2024 study linking the supplements to a reduction in cancer development, other research has found no such benefit. Nor have the supplements been seen to improve symptoms of depression.
So while such supplements – which US adults spend an estimated US$1 billion on each year – aren’t bad for you, the researchers add that it’s important to be realistic about the purported benefits.
“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,” Yassine adds.
“Living a healthy lifestyle is the brain’s equivalent of getting regular car maintenance and high-quality oil changes. The brain is more likely to lose greater function if health issues in other parts of the body go unaddressed, in the same way that car engines stop working if regular maintenance is skipped.”
The team is now looking at why fish-oil supplements cross into the brain but may not have any impact once there. The researchers’ earlier work hinted that PUFAs may be more effective when metabolized through food – like with an omega-3-rich Mediterranean-style diet – rather than as a pill.
“We’re focused on better understanding how the brain processes omega-3s and whether factors, such as poor health, dietary pattern, genetic risk and age, may change the brain’s ability to effectively absorb and use omega-3s,” Yassine says. “We are working to develop medications that may help the brain better utilize these nutrients to preserve cognitive function.”
The study was published in the journal eBioMedicine.
Source: Keck Medicine of USC
Fact-checked by Mike McRae
