Adipose Reserves and Survival: Protective in Prefrail but Ineffective in Frail Oldest-Old

Among the oldest-old, the impact of body composition on survival outcomes exhibits pronounced heterogeneity. Although the obesity paradox has been widely discussed, clear evidence is still lacking regarding whether the biological effects of adipose reserves are modulated by functional status. Therefore, this study aims to investigate the association between adipose reserve indicators and long-term all-cause mortality risk in the oldest-old and to elucidate the regulatory role of frailty, thereby providing an evidence-based foundation for precision clinical health management.

This prospective cohort study included 529 community-dwelling oldest-old individuals. Participants were categorized into prefrailty and frailty groups at baseline using the Fried frailty phenotype. Bioelectrical impedance analysis was utilized to measure body composition. Stratified multivariate Cox proportional hazards regression models were employed to evaluate the relationship between adipose indicators and all-cause mortality. Additionally, restricted cubic splines (RCS) and Kaplan-Meier curves were used to analyse survival heterogeneity.

During a median follow-up of 3.84 years, 88 deaths (16.6%) occurred. In the prefrail oldest-old, adipose reserves exhibited significant protective effects on survival: The fully adjusted model showed that PBF (HR = 0.92, 95% CI: 0.87-0.98, p = 0.006), VFA (HR = 0.99, 95% CI: 0.97-0.99, p = 0.013) and WHR (HR = 0.91, 95% CI: 0.86-0.95, p < 0.001) were all inversely associated with mortality risk. In contrast, these protective effects vanished in the frail oldest-old (all p > 0.05), suggesting that the benefits of adipose tissue are contingent upon the individual's basal functional reserve. RCS analysis revealed a linear dose-response relationship between adipose indicators and mortality risk (all p for non-linearity > 0.05), with no significant threshold effect observed. Interaction analyses confirmed that frailty status significantly modulated the prognostic value of adipose metrics (p < 0.05), with protective effects restricted exclusively to prefrail individuals. Kaplan-Meier curves confirmed that individuals in the prefrailty stage with higher adipose reserves achieved the highest survival rates (all Log-rank p < 0.001).

These findings suggest that the protective effect of adipose reserves is frailty-dependent in the oldest-old, and that weight management strategies should consider baseline functional status.