Trajectory of frailty among the older people in a community setting: A cohort study from the Shizuoka Kokuho Database

BACKGROUND: Long-term population-level evidence on frailty trajectories, particularly among the oldest-old, remains limited. AIMS: To evaluate 6-year frailty trajectories in community-dwelling adults aged ≥ 50 years. METHODS: We conducted a cohort study using a regional Japanese administrative claims database from 2012 to 2020. Frailty was measured using the electronic Frailty Index. Inverse probability of censoring weighting accounted for insurance-plan disenrollment, and weighted multinomial logistic regression estimated adjusted 6-year transition probabilities. RESULTS: The cohort included 1,040,663 adults aged ≥ 50 years (mean age, 73.2 years; 58.6% women). Six-year final status worsened with baseline frailty severity: death increased from 12.7% among fit individuals to 23.8%, 34.7%, and 49.1% among those with mild, moderate, and severe frailty. Among those with severe frailty, recovery to fit status occurred in 2.6%, and recovery to fit or mild frailty in 9.0%; 91.0% died or were in moderate-to-severe frailty. Age- and sex-specific patterns differed. Among fit adults aged 65-74 years, women had lower mortality than men (4.3% vs. 8.7%) and higher probabilities of being alive with mild or moderate frailty (26.6% vs. 21.8%; 6.1% vs. 4.9%). Among fit adults aged ≥ 85 years, death was the dominant final state, although women had lower mortality (53.9% vs. 59.0%) and higher fit status (21.7% vs. 18.8%). DISCUSSION: Severe frailty was rarely followed by recovery to fit or mild status. Sex differences in frailty trajectories varied across age groups. CONCLUSIONS: These findings highlight severe frailty as a late high-risk state and may inform age- and sex-specific frailty risk stratification and care planning.