Social Support’s Dual Mechanisms in the Loneliness–Frailty Link Among Older Adults with Diabetes in Beijing: A Cross-Sectional Study of Mediation and Moderation

<b>Background:</b> The mechanisms linking loneliness to frailty in older adults with diabetes remain unclear. Guided by the Loneliness-Health Outcomes Model, this study is the first to simultaneously validate the dual mechanisms (mediation and moderation) of social support in the loneliness-frailty relationship among older Chinese adults with diabetes. Methods: A cross-sectional study enrolled 442 community-dwelling adults aged ≥60 years with type 2 diabetes in Beijing. Standardized scales assessed loneliness (UCLA Loneliness Scale), frailty (Tilburg Frailty Indicator), and social support (SSRS). Analyses included Pearson's correlations, hierarchical regression, and PROCESS macro to evaluate mediating/moderating effects, after adjusting for demographics and comorbidities. <b>Results:</b> The frailty prevalence was 55.2%. Loneliness was positively correlated with frailty (r = 0.327, <i>p</i> < 0.01), while social support showed inverse associations with both loneliness (r = -0.496) and frailty (r = -0.315) (<i>p</i> < 0.01). Social support partially mediated loneliness's effect on frailty (indirect effect: 30.86%; 95% CI: 0.028-0.087) and moderated this relationship (interaction β = -0.003, <i>p</i> = 0.011). High-risk clusters (e.g., aged ≥80 years, widowed, and isolated individuals) exhibited combined "high loneliness-low support-high frailty" profiles. <b>Conclusions:</b> Social support reduces the frailty risk through dual mechanisms. These findings advocate for tiered clinical interventions: (1) targeted home-visit systems and resource allocation for high-risk subgroups (e.g., solo-living elders aged ≥80 years); and (2) the integration of social support screening into routine diabetes care to identify individuals below the protective threshold (SSRS < 45.47). These findings advance psychosocially informed strategies for diabetes management in aging populations.