Disability transitions and life expectancy: a national longitudinal study on social isolation and loneliness in China

Functional disability among older adults represents a dynamic process characterized by bidirectional transitions between states rather than a static condition. Social isolation and loneliness have emerged as potentially modifiable determinants of functional outcomes, yet evidence specifically examining their effects on disability state transitions remains limited.

To examine the independent and interactive associations of social isolation and loneliness with disability state transitions and life expectancy among Chinese adults aged ≥45 years.

We analyzed data from 20,954 adults aged ≥45 years in the China Health and Retirement Longitudinal Study (2011-2020). Continuous-time multi-state Markov models examined transitions among four states: no disability, mild disability, severe disability, and death. Life expectancy measures were estimated through numerical integration. Four progressively adjusted models evaluated independent and interactive effects.

Social isolation significantly increased risks of transitioning from no disability to mild disability (hazard ratio [HR]=1.19, 95% confidence interval [CI]: 1.06-1.33) and from severe disability to death (HR = 1.33, 95% CI: 1.14-1.54), while reducing recovery likelihood from mild disability (HR = 0.88, 95% CI: 0.78-1.00). Loneliness independently elevated mild disability onset risk (HR = 1.16, 95% CI: 1.06-1.27) and decreased recovery probability (HR = 0.89, 95% CI: 0.81-0.97). Their interaction increased mild-to-severe disability deterioration risk (HR = 1.56, 95% CI: 1.13-2.15). At age 45, social isolation reduced total life expectancy by 3.18 years and loneliness by 2.13 years, primarily through compression of disability-free years.

Social isolation and loneliness synergistically influence disability trajectories by affecting both worsening and recovery transitions, with disproportionate impacts on vulnerable subpopulations.