Domain-specific trends in healthy life expectancy among Chinese older adults: Compression, expansion, and dynamic equilibrium.

Background: Amid rising global life expectancy, the debate over whether population aging entails a "compression" or an "expansion" of morbidity remains unresolved. Previous evidence, drawn largely from Western nations and often reliant on cross-sectional data or single health indicators, has produced mixed findings. This study addresses this gap by investigating the health trajectory of older adults in China, examining whether it reflects morbidity compression or expansion across multiple health domains. Methods: We analyzed 20 years of longitudinal data (1998-2018) from the Chinese Longitudinal Healthy Longevity Survey (CLHLS), comprising 93,581 observations of birth cohorts from 1895 to 1949. To overcome the limitations of prevalence-based measures, we employed continuous-time multi-state Markov models for interval-censored data. This approach enabled us to estimate cohort-specific transition probabilities (i.e., onset, recovery, and mortality) and compute Healthy Life Expectancy (HLE) across three distinct domains: cognitive function, physical independence (ADL), and major chronic diseases. Results: After controlling for age and sex, we observed divergent health trajectories across successive birth cohorts. In the cognitive domain, a relative compression of morbidity emerged, characterized by a delayed onset of impairment and a reduced proportion of total life expectancy (TLE) spent with cognitive deficits. The functional (ADL) domain, however, exhibited a pattern of dynamic equilibrium, with the proportion of TLE lived with disability remaining highly stable or showing only a marginal, subtle decline across cohorts. Conversely, the chronic disease domain revealed a pronounced morbidity expansion. While the incidence of major chronic diseases declined only marginally across cohorts, the associated mortality risk decreased substantially. Consequently, later-born cohorts are living more absolute years, and a greater proportion of their TLE, with chronic conditions. Conclusions: The health transition among older adults in China is highly domain-specific, characterized by a compression of cognitive morbidity, a dynamic equilibrium in physical functioning, and an expansion of chronic disease morbidity. More recent cohorts are maintaining their cognitive clarity and physical autonomy (proportionately) for longer, yet this is increasingly occurring alongside prolonged periods of chronic illness. These findings challenge the conventional compression-versus-expansion dichotomy and highlight the need for public health systems in rapidly aging societies to shift focus from acute treatment toward proactive chronic disease management and integrated long-term care.