Longitudinal trajectories of intrinsic capacity and their association with quality of life and disability

Abstract

Objectives: Intrinsic capacity (IC) is a key concept within the World Health Organization's (WHO) healthy aging model. The systematic assessment of IC could provide a better understanding of the functional trajectories of individuals. Our aims were to identify the longitudinal trajectories of IC and estimate their association with quality of life and disability.

Study design: The study data comes from the three waves of the WHO Study on global AGEing and adult health (SAGE) in Mexico (2009, 2014, 2017). In total, 2735 adults aged 50 years or more were included. An IC score was constructed using item response theory. We used growth mixture modeling (GMM) to investigate the longitudinal trajectories of IC. Three-level linear mixed effect models were used to estimate the associations of IC with quality of life and disability.

Main outcome measures: Disability was measured using the WHO Disability Assessment Schedule (WHODAS 2.0) and quality of life using the WHOQOL (WHO Quality of Life) instrument.

Results: Three classes were identified: low baseline IC with a steeply decreasing trajectory, medium baseline IC with a slightly decreasing trajectory, and high baseline IC with a moderately increasing trajectory. The class with the better trajectory (higher baseline IC score and a moderately increasing pattern) exhibited higher quality-of-life scores and lower disability scores.

Conclusions: The findings show that older Mexican adults exhibit different IC trajectories, and that these may be associated with quality of life and disability. Results highlight the need for health policies and strategies to maintain intrinsic capacity and to promote primary prevention.

Keywords: Disability; Growth mixture modeling; Intrinsic capacity; Longitudinal trajectories; Quality of life.