Frailty incidence proportion is more influenced by age than by time period: A retrospective study from 2012 to 2022

AIM: This study aimed to clarify the factors influencing the frailty incidence proportion, focusing on age and time period effects. METHODS: A frailty survey using the basic checklist was carried out in two age groups-65 years (baseline; 1288 participants) to 75 years, and 70 (baseline; 686 participants) to 80 years-at 5-year intervals over a 10-year period (2012-2022) among older adults not certified for long-term care in City A, Tochigi Prefecture. Frailty incidence proportion was defined as the occurrence of frailty after 5 years among robust or pre-frail persons at baseline. Frailty incidence proportions were calculated at 5-year intervals, and associated factors were examined. The 2017-2022 period included the coronavirus disease 2019 (COVID-19) pandemic period. RESULTS: The frailty incidence proportion was 5.4% in the 65-70 years group during 2012-2017 (associated with outdoor activity [P = 0.002] and depression [P < 0.001]), and 8.6% in the same participants followed up as the 70-75 years group during 2017-2022 (associated with outdoor activity [P = 0.001], cognitive function [P = 0.016] and oral function [P = 0.002]). Among another age group, the incidence was 10.9% in the 70-75 years group during 2012-2017 (associated with outdoor activity [P = 0.024], depression [P = 0.003], and physical function [P = 0.026]), and 19.9% in the same individuals followed up as the 75-80 years group during 2017-2022 (associated with oral function [P = 0.008] and physical function [P = 0.001]). CONCLUSION: The frailty incidence proportion is more influenced by age (≥75 years) than by time period (before or including the COVID-19 pandemic). Effective frailty prevention requires tailored approaches for each age group. Geriatr Gerontol Int 2025; 25: 918-924.