A new study is raising questions about the long-standing belief that omega-3 supplements protect brain health, suggesting they may be associated with faster cognitive decline in older adults.

Researchers analyzing data from the Alzheimer’s Disease Neuroimaging Initiative tracked more than 800 elderly participants for up to five years. They found that individuals who reported using omega-3 supplements showed a steeper decline in memory, thinking ability, and overall cognitive performance compared to those who did not take them.

The analysis carefully matched participants by age, sex, genetic risk factors such as APOE ε4 status, and baseline cognitive condition to reduce bias between groups. Despite this, omega-3 users consistently performed worse over time on standard assessments including the Mini-Mental State Examination (MMSE), ADAS-Cog13, and Clinical Dementia Rating scales.

The decline observed was not minor. Instead, the data suggested a measurable and faster deterioration in cognitive function among supplement users during the study period.

Interestingly, the effect did not appear to be driven by typical Alzheimer’s disease hallmarks like amyloid plaque buildup or brain shrinkage. Instead, brain imaging using FDG-PET scans pointed to reduced glucose metabolism in regions of the brain that are usually vulnerable in Alzheimer’s disease.

However, the researchers stress that the findings do not establish causation. Because the study is observational, it cannot prove that omega-3 supplements directly cause cognitive decline. They also highlight limitations such as reliance on self-reported supplement use and a lack of detail on dosage, formulation quality, or oxidation levels.

While omega-3 intake from natural dietary sources like fish is still widely supported in nutritional research, the results add to growing debate over whether supplement form behaves the same way in older adults.