Trajectory and association of social vulnerability and physical frailty of the robust older adults in China and UK: evidence from cohort study

Background To explore dynamic trajectories and associations of social vulnerability and physical frailty with aging in China and the UK. Methods Data were from CHARLS and ELSA. Participants were age ≥60 years with non-frail at baseline. Cumulative deficit approach was for social vulnerability and physical frailty. Group-based trajectory modeling identified their trajectories. Cox proportional hazard and logistic regression models estimated associations between them, with sensitivity analyses. Restricted cubic splines visualized the dose-response relationship. Results UK sample older adults exhibited lower social vulnerability and physical frailty than their Chinese counterparts. Per 0.1-point increase in social vulnerability index, physical frailty risk increased by 29% in China (HR=1.29[1.20-1.37]) and 35% in the UK (HR=1.35, [1.25-1.47]). Odds of older adults being categorized into the low-robustness fast-growth group increased to 1.42 times in China (OR=1.42[1.30-1.55]) and 1.49 times in the UK (OR=1.49[1.37-1.63]). Compared with the low-vulnerability group, the high-vulnerability increasing group had 84% higher physical frailty risk in China (HR=1.84[1.60-2.12]) and 85% higher in the UK (HR=1.85[1.54-2.23]). The odds of individuals in the high-vulnerability increasing group being classified into the low-robustness fast-growth group increased 2.06 times in China (OR=2.06[1.73-2.46]) and 2.09 times higher in the UK (OR=2.09[1.73-2.51]). China had a non-linear social vulnerability-physical frailty association with a sharp increase at a threshold of 0.47, while the UK had a linear one. Conclusions Individuals with increasing social vulnerability over time had a higher physical frailty risk, particularly in lower-welfare countries. Improving self-efficacy and life control may benefit older adults regarding social vulnerability and physical frailty.