How joint trajectories of frailty and cognitive decline impact hospitalization and mortality: evidence from the Korean longitudinal study of aging 2006–2020

Abstract

Frailty and cognitive decline are major public health concerns that often progress together in older adults. However, previous studies have generally examined these two conditions separately and have tended to overlook the dynamic nature of frailty. This study analyzed how joint trajectories of frailty and cognitive decline influence the risks of hospitalization and mortality. This secondary data analysis used data from the Korean Longitudinal Study of Aging from 2006 to 2020. The study included 1,902 participants aged 65 years or older. The Frailty Index was constructed across physical and psychological domains using 33 items, including self-rated health, depressive symptoms, weight loss, limitations in activities of daily living and instrumental activities of daily living, chronic diseases, vision and hearing impairments, body mass index, and handgrip strength. Cognitive decline was measured using the Korean Mini-Mental State Examination. Group-based trajectory modeling was used to identify distinct heterogeneous subgroups with shared joint developmental pathways of frailty and cognitive decline. The risks of hospitalization and mortality were analyzed using Cox proportional hazards regression. Four trajectories were identified: stable frailty and gradual cognitive decline (SFGCD; n  = 1,003), stable frailty and progressive cognitive decline (SFPCD; n  = 423), dynamic frailty and gradual cognitive decline (DFGCD; n  = 236), and dynamic frailty and progressive cognitive decline (DFPCD; n  = 240). Compared with the SFGCD group, the DFGCD and DFPCD groups had 1.65-fold and 1.78-fold higher risks of hospitalization, respectively (95% confidence interval [CI]: 1.32–2.07 and 95% CI: 1.41–2.24, respectively). The DFPCD group had the highest hazard ratio for mortality (6.62, 95% CI: 5.06–8.97, p  < 0.001). The risk of mortality in the DFGCD group was 5.60-fold higher than that in the SFGCD group (95% CI: 4.39–7.14, p  < 0.001). The DFGCD and DFPCD groups had the shortest median survival time, at 8.0 years. The SFGCD group had the longest median survival time, at 13.0 years (95% CI: 12.74–13.26), while the SFPCD group had a similar median survival time of 12.0 years (95% CI: 11.54–12.46). This study highlights the importance of identifying target population characteristics, optimal timing, and high-risk groups to support the early detection of hospitalization and mortality risks based on frailty and cognitive decline trajectories.