Popular omega-3 supplements, widely taken by older adults “to protect the brain,” have unexpectedly been linked to faster declines in memory and thinking abilities. This conclusion was reached by Chinese researchers who analyzed data from the Alzheimer’s Disease Neuroimaging Initiative. The study was published in The Journal of Prevention of Alzheimer's Disease.

Scientists examined data from 819 older adults: 273 regularly took omega-3 supplements, while 546 did not. Participants were followed for five years, with researchers comparing cognitive test results and brain scans over time. The study found that people taking omega-3 supplements experienced faster declines in memory, attention, and other cognitive functions across several standard dementia assessment scales.

What especially surprised researchers was that the accelerated decline was not linked to the classic hallmarks of Alzheimer's Disease, such as amyloid plaque buildup or tau protein accumulation. Instead, brain scans revealed reduced glucose metabolism in the brain — a sign that nerve cells may be communicating less effectively. The authors suggest the issue could be related to dysfunction in synapses, the connections between neurons.

At the same time, the researchers stress that the study does not prove that omega-3 supplements directly cause cognitive decline. The research was observational rather than a clinical trial. This means that people who had already begun noticing memory problems may have been more likely to start taking supplements on their own.

Some experts also point out that previous studies have produced opposite findings. Several earlier papers linked higher omega-3 levels in the blood to a lower risk of dementia and slower brain aging. For example, one large study previously found that higher omega-3 levels were associated with an approximately 35–40% lower risk of early dementia.

In light of the new findings, scientists are urging more caution regarding the idea that omega-3 supplements are “universally beneficial” for brain health. The authors say further clinical trials are needed to determine who may truly benefit from such supplements and for whom they may provide little benefit — or potentially even be undesirable.