Social isolation and intrinsic capacity decline in older adults: Mediating roles of sleep duration and pain

BACKGROUND: The decline of intrinsic capacity is a key determinant of healthy aging. While social isolation is recognized as a risk factor for functional deterioration in older adults, the pathways through which it influences intrinsic capacity, particularly via sleep duration and pain, remain underexplored. OBJECTIVES: To evaluate the association between social isolation and intrinsic capacity in older adults, and to assess whether sleep duration and pain complaints mediate this relationship. METHODS: Data were obtained from the 2011 wave China Health and Retirement Longitudinal Study (CHARLS). Intrinsic capacity was assessed across five domains: locomotion, vitality, cognition, psychology, and sensory. Social isolation was measured using a composite index incorporating marital status, living arrangements, contact with children, and social participation. Logistic regression was used to examine the association between social isolation and intrinsic capacity. Mediation analyses were performed using multiple linear regression to estimate the mediating roles of sleep duration and pain complaints. RESULTS: Among 2451 participants, 1897 (77.4 %) exhibited decline in at least one intrinsic capacity domain. Prevalence of decline by domain was: locomotion (23.3 %), vitality (18.9 %), cognition (46.7 %), psychology (26.9 %), and sensory (44.2 %). 877 participants (35.8 %) were identified as socially isolated. After adjustment for sociodemographic and health-related factors, social isolation was associated with increased odds of intrinsic capacity decline. Furthermore, social isolation was positively correlated with decline in intrinsic capacity, with both sleep duration and pain complaints serving as mediators in this relationship. CONCLUSIONS: In this nationally representative sample of Chinese older adults, social isolation is associated with greater decline of intrinsic capacity, partially mediated through inadequate sleep duration and pain complaints. These findings suggest that interventions aimed at mitigating social isolation, along with integrated management of sleep and pain, may help preserve intrinsic capacity in aging populations.