Digital Inclusion as a Context-Dependent Mediating Pathway Between Social Isolation and Cognitive Functioning in Chinese and European Older Adults

Social isolation is a modifiable risk factor for cognitive decline in older adults, but the mediating role of digital inclusion across settings remains unclear. We integrated a Chinese cross-sectional study (DIHA, 2024), two longitudinal cohorts (CHARLS and SHARE), and two-sample Mendelian randomization (MR) using European-ancestry genome-wide data. Four-way decomposition assessed mediation through internet access or use and exposure-mediator interaction. Among 18,071 adults aged ≥55 years, social isolation was associated with poorer cognition across cohorts. Longitudinal mediation was clearest in SHARE, particularly for lack of group participation, but was not significant in CHARLS; DIHA mediation findings were cross-sectional and exploratory. MR linked genetically predicted loneliness and fewer leisure social activities to poorer cognition, providing complementary evidence. Digital inclusion may contribute to the relationship between social isolation and cognitive ageing, with its role warranting further investigation across settings.