An assessment of intrinsic capacity from midlife to early old age in the 1958 British birth cohort

Abstract

Intrinsic capacity (IC) summarizes functional health across multiple domains in healthy aging research, yet evidence on whether IC can be measured and tracked before older age remains limited. Using data from the 1958 British birth cohort at ages 50 and 62 (N = 7,804), we examined whether IC could be measured as a coherent, valid and longitudinally comparable construct from midlife to early old age. A second-order model applied to 30 indicators across sensory, cognitive, physical, psychological and vitality domains supported a five-domain IC construct, with scalar invariance across sweeps enabling comparison of scores over time. IC scores showed graded associations with self-rated health and chronic disease burden in the expected directions. Mean IC declined by 6.3 points on a 0-100 scale from age 50 to 62. These findings establish a basis for studying IC trajectories from midlife, before functional decline is usually clinically apparent.