Abstract
BACKGROUND: Social frailty, a state of vulnerability to social risk factors, has been linked to adverse physical, psychological, and cognitive outcomes. However, evidence on its role in the progression of multimorbidity across these domains is limited. This study examined social frailty in relation to transitions from a healthy state to physical, psychological, and cognitive conditions and to multimorbidity. METHODS: In this multi-cohort study across 24 countries in the USA, Europe, and Asia, middle-aged and older individuals with no preexisting physical, psychological, or cognitive conditions were included. Social frailty, assessed through baseline questionnaires, was defined across four domains: general resources, social behaviors, social resources, and basic social needs. Physical, psychological, and cognitive conditions were ascertained at baseline and reassessed four times during a mean follow-up of 7 years. Multi-state models and the group-based multi-trajectory model were used to examine the role of social frailty in the development of physical, psychological, and cognitive conditions and their progression to multimorbidity. RESULTS: Among the 7119 participants (mean age, 59.6 years [SD 8.5]; 3575 [50.2%] women), 778 (10.9%) were socially frail at baseline. During 49,648 person-years at risk, 2981 (41.9%) individuals progressed from a healthy state to one physical, psychological, or cognitive condition, and 1592 (22.4%) progressed to multimorbidity. Compared with socially robust participants, those with social frailty had a higher risk of progressing to any of these conditions (hazard ratio, 1.30; 95% CI, 1.17-1.44) and to multimorbidity (2.10, 1.67-2.65). Four outcome trajectories were identified, including "stably no physical, psychological or cognitive conditions" (48.0%), "increased physical conditions" (16.4%), "increased physical and psychological conditions" (8.7%), and "increased physical and cognitive conditions" (26.9%). Social frailty was associated with more than a twofold increase in risk for the latter three trajectories (odds ratios 2.34, 1.76-3.09, 2.27, 1.63-3.15 and 2.69, 2.11-3.44, respectively). The strongest associations were observed for frailty in the domains of general resources and basic social needs. CONCLUSIONS: Social frailty is associated with faster transitions from a healthy state to physical, psychological, and cognitive conditions and further progression to multimorbidity. Early identification and interventions to address social frailty may help improve health in middle-aged and older adults.