Association of Aging Trajectories in the Japan Science and Technology Agency Index of Competence With Instrumental Activities of Daily Living Among Community‐Dwelling Older Japanese Adults: The Otassha Study

要旨

AIM: The Japan Science and Technology Agency Index of Competence (JST-IC) was developed to measure competence at much higher levels than the Tokyo Metropolitan Institute of Gerontology Index of Competence (TMIG-IC), which evaluates higher-level functional capacity necessary for independent living. This study explored the JST-IC aging trajectories and their associations with instrumental activities of daily living (IADL) impairment in community-dwelling older Japanese individuals. METHODS: Participants were 665 adults who responded to the 2014 baseline survey and at least one follow-up survey (2015-2019) of the Otassha study. The JST-IC and TMIG-IC aging trajectories were identified using group-based trajectory modeling. The association with nine-year IADL impairment onset was investigated using Cox proportional hazards models. RESULTS: Three JST-IC trajectory groups were identified: high (29.5%), medium (53.1%), and low (17.3%), with scores decreasing by one to two points with increasing age over the follow-up period. High-stable (50.6%), late-onset decrease (41.1%), and early-onset decrease (8.3%) TMIG-IC trajectory groups were identified with a one- to three-point decrease in late- and early-onset groups. The low JST-IC trajectory group had an adjusted hazard ratio of 2.90 (95% confidence interval, 1.60-5.24) for IADL impairment (reference: high group). Low technology usage, information practices, and social engagement trajectories were significantly associated with IADL impairment. CONCLUSIONS: The JST-IC scores gradually declined in all groups, even among those who maintained their TMIG-IC scores. The low JST-IC trajectory group-particularly low technology usage, information practices, and social engagement-was associated with the onset of IADL impairment.

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