Wang Zhang, Jingjing Zhang, Na Gao
BACKGROUND: Cognitive decline represents a grave public health concern associated with aging, and its prevalence has been demonstrated to be associated with elevated rates of disability, dementia risk, and mortality. In recent years, social isolation has emerged as a significant social determinant that may exacerbate cognitive deterioration in older adults. METHODS: Drawing on harmonized data from five major longitudinal aging studies across 24 countries (N = 101,581), we constructed standardized indices to assess social isolation and cognitive ability. Linear mixed models and multinational meta-analyses were employed to examine their association. To address potential endogeneity and reverse causality, we further applied the System Generalized Method of Moments (System GMM), leveraging lagged cognitive outcomes as instruments to more robustly identify dynamic relationships. Finally, multilevel modeling and interaction analyses were used to investigate moderating effects at both the country level (e.g., GDP, income inequality, welfare systems) and the individual level (e.g., gender, socioeconomic status, age). RESULTS: Social isolation was significantly associated with reduced cognitive ability (pooled effect = -0.07, 95% CI = -0.08, -0.05), with consistently negative effects across memory, orientation, and executive ability. System GMM analyses supported these findings and mitigated endogeneity concerns (pooled effect = -0.44, 95% CI = -0.58, -0.30). Cross-nationally, stronger welfare systems and higher levels of economic development buffered the adverse effects, while impacts were more pronounced in vulnerable groups, including the oldest-old, women, and those with lower socioeconomic status. CONCLUSIONS: Our findings underscore the need for cross-national interventions that strengthen social support, increase opportunities for social participation, improve welfare provisions, and foster social integration to mitigate the cognitive health risks posed by social isolation, thereby promoting healthy aging globally.