Popular brain supplement may not be as beneficial as thought
Omega-3 supplements are often taken to support the heart, blood vessels and brain, especially in the elderly. But a new study has found an unexpected link: older people who took omega-3 supplements had faster cognitive decline than similar participants who did not use such supplements.
Important: this does not mean that omega-3 "causes dementia". The study was observational and found an association, not a proven cause.
Details
The authors used data from the Alzheimer's Disease Neuroimaging Initiative project. They compared elderly participants who took omega-3 supplements with a control group of people who did not take them. The groups were matched for age, gender, diagnosis and genetic risk factors, including APOE ε4, a gene variant associated with an increased risk of Alzheimer's disease.
The researchers tracked changes in cognitive performance and neuroimaging data for five years. The omega-3 group had faster declines on three major scales: the MMSE, ADAS-Cog13 and CDR-SB. The publication states that omega-3 intake was associated with a faster drop in MMSE and a faster rise in ADAS-Cog13 and CDR-SB scores, indicating cognitive deterioration.
The scientists also tested whether this association was explained by the classic hallmarks of Alzheimer's disease - amyloid accumulation, tau pathology or grey matter atrophy. According to the study, these factors did not explain the association they found.
Instead, the authors found another possible mechanism: reduced glucose metabolism in brain regions vulnerable to Alzheimer's disease. Such a rate, measured using FDG-PET, may reflect deterioration of synapses - the contacts through which neurons transmit signals.
Why it's important
Omega-3 is often thought of as an almost unquestionably beneficial supplement "for the brain." New work shows that such confidence may be premature, especially when it comes to older people and supplementation specifically to protect against cognitive decline.
That said, the data on omega-3 remains conflicting. For example, a meta-analysis of randomised trials published in Scientific Reports in 2025 concluded that omega-3s may produce modest improvements in some cognitive measures, but the authors also noted the heterogeneity of the data and varying degrees of certainty of the evidence for individual cognitive domains.
So the main conclusion is not that omega-3 is "bad for everyone." The more correct conclusion is that supplements should not be taken as a guaranteed prevention of memory impairment, and that taking them - especially in older people and with pre-existing cognitive problems - is best discussed with a doctor.
Background
Omega-3 fatty acids, including EPA and DHA, are indeed important to the body and are found in oily fish, seafood, some plant foods and supplements. But the effects of food sources and the effects of capsules are not the same thing.
The new study is specifically about supplements, not fish in the diet. Therefore, it cannot be used as an argument against a balanced diet or foods rich in omega-3. Rather, it emphasises that supplements should not replace medical assessment of risk, nutrition and general health.
Source
A study by Zheng-Bin Liao et al The association between omega-3 supplementation and cognitive decline in older adults is published in The Journal of Prevention of Alzheimer's Disease in 2026. The authors used ADNI data, cognitive scales and neuroimaging measures to assess the association between omega-3 supplementation and cognitive changes in older adults.