Assessment of Frailty Index at 66 Years of Age and Association With Age-Related Diseases, Disability, and Death Over 10 Years in Korea.

Importance: A frailty index has been proposed as a measure of aging among older individuals. However, few studies have examined whether a frailty index measured at the same chronologic age at younger ages could forecast the development of new age-related conditions. Objective: To examine the association of the frailty index at 66 years of age with incident age-related diseases, disability, and death over 10 years. Design, Setting, and Participants: This retrospective nationwide cohort study used the Korean National Health Insurance database to identify 968 885 Korean individuals who attended the National Screening Program for Transitional Ages at 66 years of age between January 1, 2007, and December 31, 2017. Data were analyzed from October 1, 2020, to January 2022. Exposures: Frailty was defined using a 39-item frailty index ranging from 0 to 1.00 as robust (<0.15), prefrail (0.15-0.24), mildly frail (0.25-0.34), and moderately to severely frail (≥0.35). Main Outcomes and Measures: The primary outcome was all-cause death. Secondary outcomes were 8 age-related chronic diseases (congestive heart failure, coronary artery disease, stroke, type 2 diabetes, cancer, dementia, fall, and fracture) and disability qualifying for long-term care services. Cox proportional hazards regression and cause-specific and subdistribution hazards regression were used to examine hazard ratios (HRs) and 95% CIs for the outcomes until the earliest of date of death, the occurrence of relevant age-related conditions, 10 years from the screening examination, or December 31, 2019. Results: Among the 968 885 participants included in the analysis (517 052 women [53.4%]), the majority were classified as robust (65.2%) or prefrail (28.2%); only a small fraction were classified as mildly frail (5.7%) or moderately to severely frail (1.0%). The mean frailty index was 0.13 (SD, 0.07), and 64 415 (6.6%) were frail. Compared with the robust group, those in the moderately to severely frail group were more likely to be women (47.8% vs 61.7%), receiving medical aid insurance for low income (2.1% vs 18.9%), and less active (median, 657 [IQR, 219-1133] vs 319 [IQR, 0-693] metabolic equivalent task [min/wk]). After adjusting for sociodemographic and lifestyle characteristics, moderate to severe frailty was associated with increased rates of death (HR, 4.43 [95% CI, 4.24-4.64]) and new diagnosis of all chronic diseases, including congestive heart failure (adjusted cause-specific HR, 2.90 [95% CI, 2.67-3.15]), coronary artery disease (adjusted cause-specific HR, 1.98 [95% CI, 1.85-2.12]), stroke (adjusted cause-specific HR, 2.22 [95% CI, 2.10-2.34]), diabetes (adjusted cause-specific HR, 2.34 [95% CI, 2.21-2.47]), cancer (adjusted cause-specific HR, 1.10 [95% CI, 1.03-1.18]), dementia (adjusted cause-specific HR, 3.59 [95% CI, 3.42-3.77]), fall (adjusted cause-specific HR, 2.76 [95% CI, 2.29-3.32]), fracture (adjusted cause-specific HR, 1.54 [95% CI, 1.48-1.62]), and disability (adjusted cause-specific HR, 10.85 [95% CI, 10.00-11.70]). Frailty was associated with increased 10-year incidence of all the outcomes, except for cancer (moderate to severe frailty adjusted subdistribution HR, 0.99 [95% CI, 0.92-1.06]). Frailty at 66 years of age was associated with greater acquisition of age-related conditions (mean [SD] conditions per year for the robust group, 0.14 [0.32]; for the moderately to severely frail group, 0.45 [0.87]) in the next 10 years. Conclusions and Relevance: The findings of this cohort study suggest that a frailty index measured at 66 years of age was associated with accelerated acquisition of age-related conditions, disability, and death over the next 10 years. Measuring frailty at this age may offer opportunities to prevent age-related health decline.