Liao et al. (2026) recently reported an association between omega-3 supplementation and accelerated cognitive decline, mediated by FDG-PET hypometabolism. While clinically provocative, this observational finding warrants cautious interpretation. This Letter critiques four methodological limitations: (1) exposure misclassification, as ADNI’s binary supplement variable ignores oxidation state and formulation (pharmacy grade vs. oxidized OTC fish oil); (2) residual confounding, since propensity score matching cannot adjust for subtle preclinical worry or lifestyle factors driving supplement initiation; (3) mechanistic overreach, as FDG hypometabolism reflects composite metabolic/inflammatory processes, not isolated synaptic dysfunction; and (4) context dependency, where effects likely hinge on baseline omega-3 status and individual oxidative load. We propose actionable refinements: biomarker-anchored dose modeling (serum EPA+DHA), negative-control sensitivity analyses, partial volume-corrected FDG mediation, and CSF synaptic marker integration. Rather than a universal “harm” signal, this paradoxical association should be framed as hypothesis generating, urging personalized prevention strategies over blanket clinical warnings.To the Editor: