In 4,863 U.S. adults aged 20–79 from NHANES 2021–2023, erythrocyte EPA and DHA concentrations rose with age while n-6 PUFAs — particularly linoleic acid, DGLA, and ALA — declined. Crucially, among the fasting subsample (n=2,822), those with the highest omega-3 index (≥8% EPA+DHA in red blood cells) showed a PhenoAge acceleration roughly 4.7 years lower than those with minimal omega-3 status, suggesting a meaningful biological age advantage associated with robust long-chain n-3 PUFA levels.
PhenoAge, developed by Morgan Levine, aggregates nine clinical biomarkers — including albumin, creatinine, glucose, CRP, and white cell count — into a composite biological age score that predicts mortality better than chronological age alone. A 4.7-year difference in this metric is substantively large, comparable to effect sizes reported for regular vigorous exercise or non-smoking. The finding adds population-level weight to smaller clinical cohorts, including prior German data, that identified similar PUFA shifts with aging.
However, the cross-sectional design prevents any causal inference — people with higher omega-3 status may differ systematically in diet quality, supplement use, or socioeconomic status. Red blood cell fatty acid composition reflects weeks-to-months of intake, not lifelong exposure. Confounding by fish consumption, omega-3 supplementation, and overall dietary pattern is difficult to fully disentangle. As a preprint not yet peer-reviewed, these results require independent validation before influencing clinical recommendations. Nonetheless, the study is confirmatory and scale is a genuine strength.