Drivers of Frailty from Adulthood into Old Age: Results from a 27-year Longitudinal Population-Based Study in Sweden

Background. Frailty is a strong predictor of adverse aging outcomes. However, the longitudinal drivers of frailty are not well understood. This study aimed at investigating the longitudinal trajectories of a frailty index (FI) from adulthood to late life and identifying the predictors of the level and rate of change in FI. Methods. An age-based latent growth curve analysis was performed in the Swedish Adoption/Twin Study of Aging (N=1,842; aged 29-102 years) using data from up to 15 measurement waves across 27 years. A 42-item FI was used to measure frailty at each wave. Results. A bilinear, two-slope model with a turning point at age 65 best described the age-related change in FI, showing that the rate of increase in frailty was more than twice as fast after age 65. Underweight, obesity, female sex, overweight, being separated from one9s co-twin during childhood, smoking, poor social support and low physical activity were associated with a higher level of FI at age 65, with underweight having the largest effect size. When tested as time-varying predictors, underweight and higher social support were associated with a steeper increase in FI before age 65, whereas overweight and obesity were associated with less steep increase in FI after age 65. Conclusions. Predictors for the level and rate of change in frailty are largely actionable and could provide targets for intervention. Underweight increased the risk of higher FI trajectory until age 65, whereas being overweight or obese were associated with slower progression of frailty towards the oldest ages.