The vitality domain of intrinsic capacity: A scoping review of conceptual frameworks and measurements.

BACKGROUND

Intrinsic capacity (IC) is a composite indicator of physical and mental capacities that are critical for healthy aging. IC comprises five domains, with "vitality" gaining most attention due to its potential impact on functional and physiological reserves with increasing age. The World Health Organization 2022 framework redefined vitality as an underlying physiological determinant of IC. However, the concept and measurement of vitality and its empirical validation are not well defined.

OBJECTIVES

This scoping review aims to: (1) map the conceptual frameworks underpinning vitality within the IC domain and (2) identify existing measures used to assess vitality.

METHODS

A systematic search of MEDLINE, PubMed, Embase, Web of Science, and WHO databases (2003-2023) using Arksey and O'Malley's framework and PRISMA-ScR guidelines. Studies involving adults ≥50 years old that addressed vitality in IC were included. We extracted data on conceptual frameworks, measurement tools, and construct validity.

RESULTS

Eighty-one studies met the inclusion criteria. Initial frameworks of vitality focused on nutritional indicators, while recent concepts include neuromuscular function, metabolism, and immune-stress responses. However, operationalization of these concepts remains inconsistent, with most studies relying on anthropometry, appetite, weight loss, and handgrip strength, while immune and stress response-related biomarkers were rarely assessed. Only 10.5 % of studies evaluated construct validity of vitality, and limited studies validated the potential roles of vitality underpinning the other expressed capacities.

CONCLUSIONS

Currently, vitality within IC varies in definitions and measurement approaches, with a predominant focus on nutrition and muscle strength. Empirical validation of vitality's role as a foundational IC domain remains limited. Expanding the scope of vitality to include metabolic and immune markers, and deeper examination of the interactions between vitality with other IC domains may enhance understanding and improve assessment frameworks for healthy aging.