Measuring intrinsic capacity among Canadian adults: a population-based study using the Canadian Longitudinal Study on Aging (CLSA)

Background Intrinsic capacity (IC) is the composite of an individual's physical and mental capacities, capturing underlying reserve and heterogeneity in the aging process. Despite growing recognition of the importance of IC, inconsistencies in measuring IC persist. The objective of this study was to develop a measure of IC in Canadian adults and to assess its psychometric properties. Methods Data from the Canadian Longitudinal Study on Aging (n = 30,097; 50.9% female; 96.0% White) were used. Candidate measures of IC were identified through key documentation and expert consultation. A total of 18 variables were identified to be suitable. Exploratory factor analysis (EFA) was conducted, followed by a confirmatory factor analysis (CFA) using bifactor item response theory to compute the IC score. Reliability, construct validity and criterion validity were tested. Findings EFA revealed a seven-factor structure including Locomotion, Vitality (body composition), Vitality (inflammation), Vitality (blood pressure), Psychological, Sensory/Balance and Cognition. Using CFA, a bifactor model produced an overall general IC score, which showed acceptable reliability, alongside subdomain scores, which showed low reliability and should be considered exploratory and hypothesis-generating. Construct validity was supported by expected correlations with related measures, including self-reported healthy aging (r = −0.24), frailty (r = −0.36), functional impairment (r = −0.29), and epigenetic age (r = −0.42). Known-groups validity was demonstrated by declining IC scores across age groups. IC scores demonstrated acceptable discrimination for mortality (AUC = 0.71–0.74). Interpretation The overall IC score showed acceptable psychometric properties and can be used to characterize IC, whereas the subdomain scores remain exploratory and hypothesis-generating. By incorporating multiple physiological markers, this study advances the measurement of IC and supports earlier identification of individuals at risk of functional decline, with potential application to population-level monitoring of capacity. Longitudinal work is needed to establish its value for monitoring change over time. Funding This research was conducted using data from the Canadian Longitudinal Study on Aging (CLSA), funded by the Canadian Institutes of Health Research and the Canada Foundation for Innovation. The authors are supported by the Raymond and Margaret Labarge Chair in Research and Knowledge Application for Optimal Aging, the Canada Research Chairs Program, the Canadian Institutes of Health Research, and the Hamilton Health Sciences Foundation.