The caffeine spectrum: associations of intake, metabolites, and metabolite ratios with biological aging acceleration, frailty and mortality

While caffeine consumption is linked to numerous health outcomes, its role in the aging process remains unclear. We aimed to investigate the cross-sectional associations of caffeine exposures (intake, metabolites, metabolite ratios) with biological age acceleration (BAA) and frailty, as well as their prospective associations with all-cause mortality, while assessing BAA’s mediating role. This study included 6,150 representative U.S. adults (median age: 46.00 years, 49.5% male). Dietary caffeine intake and 14 caffeine metabolites were assessed. BAA was derived from both clinical ( N = 5,890 for KDMAgeAccel and N = 3,229 for PhenoAgeAccel) and epigenetic biomarkers ( N = 619), and frailty was quantified using a 36-item modified Frailty Index (FI). Associations between caffeine-related exposures and aging outcomes (FI and mortality) were evaluated using survey-weighted regression models, and mediation analysis was employed to test the mediating role of BAA. Benjamini-Hochberg false-discovery-rate (FDR) correction was applied to account for multiple testing. Higher dietary caffeine intake, selected caffeine metabolites (mainly xanthines), and higher spot-urine metabolite ratios were significantly and inversely associated with BAA, FI, and all-cause mortality, with the association for the paraxanthine-to-caffeine ratio remaining robustly significant after FDR correction. Significant interactions between dietary caffeine intake and caffeine-related indicators were observed. Exploratory mediation analyses suggested that physiology-based BAA metrics (KDMAgeAccel and PhenoAgeAccel) represent a potential mediation pathway in the associations of selected caffeine-related indicators with both FI and mortality. The spot-urine caffeine metabolite ratios, particularly the paraxanthine-to-caffeine ratio, showed the strongest inverse associations with various aging-related outcomes in both the primary analyses and rigorous sensitivity analyses, and contributed to the most significant mediation pathways. Our findings provide epidemiological evidence that the spot-urine paraxanthine-to-caffeine ratio correlates with healthier aging-related phenotypes cross-sectionally and reduced mortality prospectively. Rather than a validated biological marker, this ratio represents an exploratory association signal requiring future prospective and mechanistic validation.