Co-deteriorating trajectories of cognitive function and social frailty among Chinese older adults: a group-based dual trajectory analysis

Although previous studies have begun to explore social frailty, cognitive function, and their respective trajectories among older adults, empirical evidence regarding the bidirectional associations between these trajectories remains limited. Clarifying this dynamic relationship is essential for informing effective prevention and intervention strategies. Data were obtained from four waves (2016, 2018, 2020, and 2023) of the China Longitudinal Aging Social Survey (CLASS), with the 2016 wave serving as the study baseline. Group-based trajectory modeling (GBTM) and group-based dual trajectory modeling (GBDTM) were employed to identify trajectories of social frailty and cognitive function. Subsequently, multinomial logistic regression was used to examine the bidirectional associations between these trajectories. Stratified analyses and interaction tests were further conducted to assess heterogeneity and joint effects based on socioeconomic factors. This study identified three trajectories of social frailty: low stable, moderate increasing, and high increasing and four distinct cognitive trajectories: high stable, moderate declining, low declining, and increasing. Unfavorable trajectories of social frailty and cognitive function tended to co-occur and were bidirectionally associated. Specifically, less favorable social frailty trajectories were associated with higher risks of unfavorable cognitive trajectories, and unfavorable cognitive trajectories were likewise associated with higher risks of worsening social frailty trajectories. Stratified analyses revealed that older age and being married were associated with a higher likelihood of unfavorable bidirectional transitions between social frailty and cognitive function trajectories. Men were more vulnerable to this co-deterioration process, whereas higher education exerted a protective moderating effect by reducing the risk of adverse transitions. This study identified distinct longitudinal patterns of social frailty and cognitive function among Chinese older adults. Unfavorable trajectories in the two domains tended to co-occur and were bidirectionally associated, although causality cannot be established. These findings support the potential value of jointly monitoring social frailty and cognitive function and highlight the need for further research with longer follow-up and stronger causal designs.