Can Social Mobility Impact Frailty Trajectories of Chinese Adults in Later Life? A Nationwide Longitudinal Study

Background and Objectives Evidence remains unclear on the impact of life-course socioeconomic position (SEP) mobility on frailty trajectories in later life. We aim to examine the longitudinal effects of social mobility on frailty trajectories among Chinese middle-aged and older populations. Research Design and Methods A total of 13 239 participants aged 45 and older from the 2011-2018 China Health and Retirement Longitudinal Study were analyzed. Based on changes in SEP from childhood to adulthood, 5 patterns of social mobility were established. A 32-item deficit cumulative frailty index (FI) was developed to evaluate frailty trajectories at each follow-up. Linear mixed-effects models were used to examine the longitudinal association of the 5 social mobility patterns with the frailty trajectory. Results The trajectory of late-life FI increased across all 5 social mobility groups during the follow-up. The FI trajectory had the largest disparity between stable high SEP and stable low SEP, with a faster increase in FI of 0.489 (95% confidence interval [CI]: 0.327-0.650, p < .001) in the stable low versus stable high SEP group. The FI trajectories of individuals in the upward and downward mobility groups fall between those in the stable high SEP and low SEP groups. Specifically, compared to the stable high SEP group, the increase in FI was 0.229 (95% CI: 0.098-0.360, p = .001) faster in the downward mobility group, and 0.145 (95% CI: 0.017-0.273, p = .03) faster in the upward mobility group. The impact of social mobility on frailty trajectories was more pronounced among middle-aged adults and women. Discussion and Implications These findings emphasize that policies to identify vulnerable populations and reduce frailty inequalities should focus on the socioeconomic environment across the life course, with particular attention paid to those with consistently low SEP and downward mobility.