Mapping the diverse trajectories of intrinsic capacity and their key drivers in China's aging population

Intrinsic capacity (IC) is central to healthy aging. Understanding its longitudinal change is crucial for proactive health planning. Yet evidence on distinct IC trajectories and their determinants in China remains limited, constraining targeted interventions.

We analyzed cohort data from participants aged 50 years and older in the World Health Organization's Study on Global AGEing and Adult Health (WHO-SAGE) China cohort. A composite IC score was constructed based on the WHO framework, encompassing locomotion, cognition, psychological, sensory, and vitality domains. We employed Latent Class Growth Analysis (LCGA) and Growth Mixture Modeling (GMM) to identify distinct IC trajectories. Multinomial logistic regression was then used to investigate associations between these trajectories and a comprehensive set of socio-demographic, individual health-related, and environmental factors. The relative importance of identified factors was evaluated using SHapley Additive exPlanations (SHAP) values.

Four IC trajectories were identified: High and Stable IC (HSI), High and Slowly Declining IC (HSDI), Moderate and Rapidly Declining IC (MRDI), and Low and Rapidly Declining IC (LRDI). Older age (OR = 5.79, 95% CI 4.73-7.10), female sex (OR = 2.86, 95% CI 2.18-3.75), comorbidity (OR = 8.15, 95% CI 5.07-13.10), low income (OR = 4.11, 95% CI 2.82-5.99), low paternal education (OR = 2.04, 95% CI 1.41-2.94), and higher physical risk scores (OR = 1.18, 95% CI 1.02-1.37) were associated with a greater likelihood of belonging to the LRDI trajectory and were also associated with other unfavorable profiles. Clean cooking fuel use (OR = 0.17, 95% CI 0.11-0.26) and being married (OR = 0.53, 95% CI 0.34-0.82) were associated with a lower likelihood of belonging to the LRDI trajectory. SHAP identified age as the most influential contributor across all trajectories, while income, cooking fuel, ambient temperature, relative humidity, sex, education, and comorbidity also showed substantial contributions across different trajectory patterns.

The study identified substantial heterogeneity in IC trajectories among Chinese middle-aged and older adults. Socio-demographic, individual health-related, and environmental factors were associated with distinct trajectory patterns. Potentially modifiable contextual factors, particularly household cooking fuel and environmental conditions, may warrant greater attention in future healthy ageing strategies.