ABSTRACT
This study aimed to clarify the longitudinal relationship between social interaction and cognitive function in later life. Longitudinal data were analysed from a cohort of 340 older adults across three waves (2014–2020). We employed Bayesian Cross-Lagged Panel Models (CLPM) and Random-Intercept Cross-Lagged Panel Models (RI-CLPM) to examine the reciprocal association between the Index of Social Interaction (ISI) and cognitive impairment risk. Higher social interaction at baseline (T1, 2014) predicted a lower risk of later cognitive impairment. After partitioning out trait-like differences, a robust within-person protective effect remained: a positive deviation in an individual’s social interaction at baseline (relative to their own average) significantly predicted a reduced risk of later cognitive impairment. Autoregressive effects of cognitive risk were primarily driven by between-person stability. No significant cross-lagged effects were observed for changes between later timepoints, potentially reflecting the impact of advanced ageing or the COVID-19 pandemic during the final wave. Proactively increasing social engagement in the young-old stage provides a significant protective effect against cognitive decline. These findings support social prescribing as a viable non-pharmacological strategy and emphasize that interventions targeting dynamic behavioural changes may be more effective than those focusing solely on baseline social status.