Intrinsic capacity and comorbidity burden capture distinct but age-driven dimensions of health in older postmenopausal women

BACKGROUND: Intrinsic capacity (IC) and comorbidity burden are both associated with health outcomes in older postmenopausal women, yet whether they capture independent dimensions of health remains unclear. AIMS: To examine whether comorbidity burden is independently associated with IC in older postmenopausal women, and to evaluate the role of age as a potential confounder of this relationship. METHODS: IC was evaluated across five WHO-defined domains using ICOPE-aligned tools, and the number of preserved IC components (range 0-6) was calculated as an index of functional reserve. Comorbidity burden was quantified with the Charlson Comorbidity Index (CCI). RESULTS: A total of 200 postmenopausal women were included (mean age 68.2 ± 8.5 years, range 46-89). The mean CCI score was 3.5 ± 1.9 and the mean number of preserved IC components was 3.4 ± 1.3. Preserved IC components were inversely correlated with CCI (ρ = -0.33, p < 0.001). In multivariable analysis, CCI was not independently associated with preserved IC (β = -0.036, 95% CI - 0.142 to 0.070, p = 0.505), whereas age was a strong independent predictor (β = -0.078, 95% CI - 0.100 to - 0.055, p < 0.001). The partial correlation between IC and CCI controlling for age was negligible (r = 0.003, p = 0.962). Sensitivity analyses using Poisson regression and a 5-component IC score excluding the vision domain confirmed these findings. CCI was not independently associated with any individual IC domain in domain-specific logistic regression models. DISCUSSION: The observed association between IC and comorbidity burden was largely explained by age, suggesting that these constructs capture overlapping but not identical dimensions of health vulnerability. CONCLUSIONS: IC captures dimensions of functional vulnerability not fully accounted for by comorbidity burden alone.