Allostatic load-intrinsic capacity phenotypes and adverse ageing outcomes in middle-aged and older Chinese adults

BACKGROUND: Allostatic load (AL) reflects multisystem physiological dysregulation, whereas intrinsic capacity (IC) reflects functional reserve. We examined whether cross-classification of AL and IC identified distinct risk profiles for adverse ageing outcomes. METHODS: Among 11,190 otherwise eligible participants, 8695 had sufficient AL and IC information for the non-fatal analyses, and all-cause mortality was analysed in a baseline risk set of 8973. AL was calculated from 11 biomarkers, and IC was operationalised as a proxy-based, prorated 0-9 score across five domains. Discrete-time logistic models with participant-level robust standard errors were fitted to 2011-2018 person-period data. RESULTS: Both low-IC phenotypes were associated with higher odds of functional limitation and hospitalisation compared with the low AL + high IC reference phenotype. The high AL + low IC phenotype had the largest point estimates for activities of daily living (ADL)/instrumental activities of daily living (IADL) limitation (OR 1.87, 95% CI 1.63-2.15), ADL limitation (OR 2.83, 2.37-3.40), and hospitalisation (OR 1.74, 1.52-1.99). For mortality, high AL + low IC had the largest estimate (OR 2.30, 1.74-3.04) and high AL + high IC was also associated with higher mortality (OR 1.84, 1.38-2.46). Multiplicative interactions were not statistically significant. Positive additive interaction on the odds-ratio scale was observed only for ADL limitation (RERI 0.414, 95% CI 0.012-0.804). CONCLUSION: Joint AL-IC classification identified distinct, outcome-specific risk profiles. Low IC was the more consistent risk dimension for functional limitation and hospitalisation; mortality was associated with the high-AL phenotypes. Incremental predictive performance and clinical utility were not evaluated.