How Older Adults' Physical and Mental Capacities Shift Over Time

Intrinsic capacity (IC) — the WHO-defined composite of all physical and mental capabilities of an individual — has emerged as a cornerstone metric for healthy aging. Unlike disease-based assessments, IC captures five interrelated domains: locomotion, cognition, psychological well-being, vitality, and sensory function. Because IC is dynamic and individually variable, understanding how it evolves across older adulthood is essential for designing timely interventions.

This systematic review followed PRISMA guidelines and searched PubMed, Embase, Ovid, and Web of Science through July 2024. From 173 initial records, 13 longitudinal observational cohort studies met inclusion criteria, collectively covering 45,296 participants (60.1% female, weighted mean age 71.74 years). Studies spanned two to fourteen assessment timepoints, with follow-up ranging from one year to over two decades. Eight studies originated from China, two from Mexico, and one each from France and the United States. Quality was assessed using the Newcastle-Ottawa Scale (NOS) and the GRoLTS checklist for latent trajectory studies.

When IC was expressed as a single composite score, three dominant trajectory patterns emerged across studies: a declining trajectory (sharp, moderate, or mild decline from baseline), a stable trajectory (minimal change over time), and a high trajectory (high baseline IC with a slight upward or maintained trend). When IC was decomposed into its five domains, trajectories were categorized by degree of domain impairment — robust status (no impaired domains), mild impairment (1–2 domains affected), and severe impairment (multiple domains affected with marked functional decline). One multi-trajectory analysis identified distinct sub-groups such as 'low locomotion,' 'low psychological domain,' and 'low in all domains,' further illustrating the heterogeneity of aging pathways.

Key determinants of unfavorable IC trajectories included older age, female sex, lower education, greater number of chronic diseases, unmarried status, perceived financial inadequacy, and poor self-rated health. Elevated inflammatory biomarkers — specifically IL-6, TNFR-1, and GDF-15 — were also independently associated with steeper IC decline, pointing to inflammation as a biological mechanism driving capacity loss. Adverse trajectory patterns were consistently associated with increased risks of mortality, disability, frailty, falls, nursing home admission, and diminished quality of life.

The authors note important gaps: most studies relied on secondary data from existing cohorts, used limited assessment timepoints, and rarely captured IC changes near end of life. Few studies employed experimental designs capable of establishing causality. Future research should incorporate more frequent objective measurements, diverse global populations, and intervention trials targeting modifiable IC determinants to translate trajectory knowledge into clinical practice.