Reference centiles for intrinsic capacity throughout adulthood and their association with clinical outcomes: a cross-sectional analysis from the INSPIRE-T cohort

Intrinsic capacity (IC), a function-centered construct, is defined as the composite of all physical and mental capacities of an individual. IC and surrounding environmental factors determine an individual's functional ability to do what they want or feel valued. Current literature lacks evidence on how IC varies throughout adulthood. In this study, we demonstrated a method to establish age-specific and sex-specific reference centiles for IC using the Human Translational Research Cohort of the INSPIRE Platform (975 adults, aged 20-102 years, living in the southwest France, Toulouse area). IC was operationalized as the mean score of the five key domains (cognition, locomotion, psychology, sensory and vitality) and the factor score from a bifactor model, respectively. Both IC operationalizations showed higher IC levels in young and middle age and markedly lower levels after age 65 years, with greater inter-individual variation in old age than in youth. Individuals with IC ≤10th percentile tended to have high comorbidity, prefrailty/frailty, difficulties in basic and instrumental activities of daily living and falls than individuals with IC >90th percentile. These findings suggest that IC reference centiles can help monitor the functional capacity of individuals during aging, similar to tracking children's development with growth charts.