Abstract
BACKGROUND: Baseline frailty index (FI) values have been shown to predict mortality among older adults, but little is known about the effects of changes in FI on mortality. METHODS: In a coordinated approach, we analyzed data from 4 population-based cohorts: the Health and Retirement Study (HRS), the Survey of Health, Ageing and Retirement in Europe (SHARE), the English Longitudinal Survey of Ageing (ELSA), and the Longitudinal Aging Study Amsterdam (LASA), comprising a total of 24 961 respondents (65+), 95 897 observations, up to 9 repeated FI assessments, and up to 23 years of mortality follow-up. The effect of time-varying FI on mortality was modeled with joint regression models for longitudinal and time-to-event data. RESULTS: Differences (of 0.01) in current FI levels (hazard ratio [HR] = 1.04, 95% credible interval [CI] = 1.03-1.05) and baseline FI levels (HR = 1.03, 95% CI = 1.03-1.05) were consistently associated with mortality across studies. Importantly, individuals with steeper FI growth also had a higher mortality risk: An increase in annual FI growth by 0.01 was associated with an increased mortality risk of HR = 1.56 (95% CI = 1.49-1.63) in HRS, HR = 1.24 (95% CI = 1.13-1.35) in SHARE, HR = 1.40 (95% CI = 1.25-1.52) in ELSA, and HR = 1.71 (95% CI = 1.46-2.01) in LASA. CONCLUSIONS: FI changes predicted mortality independently of baseline FI differences. Repeated assessment of frailty and individual's frailty trajectory could provide a means to anticipate further health deterioration and mortality and could thus support clinical decision making.