Longitudinal associations of chronic pain severity trajectories and number of pain site trajectories with risk of limitations in ability in daily activities: Evidence from two 10-year prospective cohort studies.

BACKGROUND AND OBJECTIVES: Chronic pain is a significant risk factor for limitations in activities of daily living (ADL). However, previous studies have mostly assessed pain severity at a single time point, overlooking its temporal variability. This study aims to explore the longitudinal associations between trajectories of chronic generalized pain severity, the number of pain sites, and trajectories of chronic site-specific pain severity with the risk of developing ADL limitations. METHODS: This study utilized longitudinal data from individuals aged 50 and above in two cohorts: the English Longitudinal Study of Ageing (ELSA) and the Korean Longitudinal Study of Aging (KLoSA). By analyzing dynamic changes in pain severity states, trajectories of chronic generalized pain severity, the number of pain sites, and chronic site-specific pain severity were identified. Cox proportional hazards models were applied to assess the associations between various pain severity trajectories and the incidence of ADL limitations. Mediation analysis was conducted to investigate the mediating effect of depression. RESULTS: The Cox proportional hazards models showed that, among trajectories of chronic generalized pain severity and pain severity at the back, feet, and knees, the persistent high-level pain and worsening pain trajectory groups exhibited the highest increased risk of ADL limitations. Additionally, all trajectories of the number of pain sites were positively associated with ADL limitation risk, with the increasing number of pain sites trajectory showing the strongest association (HR = 2.738, 95% CI: 2.147-3.492). Depression mediated the associations between various pain severity trajectories and ADL limitations. CONCLUSION: The research findings underscore the significant role of long-term, persistently high levels and progressively worsening severity of chronic systemic and localized pain in the limitations of ADL functions in older adults. Incorporating longitudinal monitoring of chronic pain severity trajectories into ADL function limitation management programs is crucial for enhancing preventive and therapeutic interventions.