Background: The prevalence of frailty is increasing as the population ages. Lifestyle interventions have shown potential in frailty prevention. Intervention studies have been generally limited by short interventions and follow-ups or by focusing on single-domain approaches. We aimed to investigate whether a 2-year multidomain lifestyle intervention prevents phenotypic pre-frailty or frailty and whether baseline factors predict phenotypic pre-frailty or frailty.

Methods: A total of 1259 participants (aged 60-77 years) in the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) were randomized to a multidomain intervention group or to a regular health advice group for 2 years. Frailty was defined by modified Fried phenotype. Pre-frail and frail participants were grouped for analyses. The prevalence of pre-frailty/frailty at baseline and at 2, 7, and 11 years, the change in prevalence from baseline, and the difference in these changes between intervention and control groups were estimated using a mixed-effects logistic regression model.

Results: The intervention reduced the risk of pre-frailty/frailty up to 7 years. The prevalence decreased in the intervention group from baseline (47%) to 2 years (42%), while it increased in the control group (45% to 49%), resulting in a -9.6-percentage point difference in the change (p = 0.007). After the active intervention period, the prevalence began to increase in both groups, but the difference in the change remained in favor of the intervention group at 7 years (-6.2 percentage points, p = 0.049). The beneficial effect was no longer evident at 11 years. Older age, lower protein intake, and a higher number of chronic diseases were strongly associated with pre-frailty/frailty.

Conclusions: A 2-year multimodal lifestyle intervention effectively prevented phenotypic pre-frailty/frailty, with sustained benefits observed up to 7 years. Continuous support for a healthy lifestyle may be necessary to prevent late-life pre-frailty or frailty.