New research suggests that omega-3 supplements, long promoted for brain health, may be associated with accelerated cognitive decline in older adults. A longitudinal study using data from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) found that participants taking omega-3 supplements experienced significantly faster deterioration in memory and thinking abilities compared to matched non-users. The analysis, published in The Journal of Prevention of Alzheimer’s Disease, followed over 800 older adults for up to five years. After matching for age, sex, genetics (including APOE ε4 status), and baseline diagnosis, omega-3 users showed steeper declines on three standard cognitive assessments: a faster drop in Mini-Mental State Examination (MMSE) scores, and faster worsening on the Alzheimer’s Disease Assessment Scale-Cognitive Subscale 13 (ADAS-Cog13) and Clinical Dementia Rating Sum of Boxes (CDR-SB). Importantly, the accelerated decline was not explained by classical Alzheimer’s biomarkers such as amyloid plaques, tau pathology, or gray matter atrophy. Instead, the researchers identified reduced cerebral glucose metabolism (measured by FDG-PET) in Alzheimer’s-vulnerable brain regions as a key mediating factor, suggesting possible negative effects on synaptic function and brain energy processing. The authors stress that this observational study cannot prove direct causation and note limitations including self-reported supplement use and lack of data on product quality or oxidation. While dietary omega-3 from fish remains generally beneficial in many studies, these findings raise important questions about routine supplementation in older adults and highlight the need for further randomized controlled trials. [Liao Z-B, Hu Z-C, Zeng G-H, et al. The association between omega-3 supplementation and cognitive decline in older adults. The Journal of Prevention of Alzheimer’s Disease. 2026. DOI 10.1016/j.tjpad.2026.100569]