Socioeconomic Differences in Trajectories of Functional Capacity Among Older Japanese: A 25-Year Longitudinal Study

Abstract

ObjectivesThere is limited research on long-term changes in functional capacity among older Japanese, who differ significantly from their counterparts in Western, developed nations. This study aimed to identify distinct trajectories of functional capacity over a 25-year period and to explore socioeconomic differences in trajectory-group membership probabilities, using a national sample of older Japanese. DesignLongitudinal panel study with 8 observation points from 1987 to 2012. Setting and ParticipantsThe data came from the National Survey of the Japanese Elderly, which consisted of 6193 samples of community-dwelling Japanese aged 60 years and older at baseline. MethodsFunctional capacity measure included basic and instrumental activities of daily living. Group-based mixture models were used for data analysis. ResultsAmong participants aged 60 to 74 years at baseline, 4 trajectories were identified: minimal disability (80.3%), late-onset disability (11.6%), early-onset disability (6.2%), and moderate disability (1.9%). Those aged ≥75 years at baseline experienced higher levels of disability but somewhat parallel trajectories, including minimal disability (73.3%), early-onset disability (11.2%), moderate disability (11.3%), and severe and worsening disability (4.2%). Lower socioeconomic status, including education and household income, was associated with a higher risk of experiencing trajectories of poorer functional capacity among those aged 60 to 74 years, but no such association existed among those aged ≥75 years. Conclusions and ImplicationsWe found that approximately 70% to 80% of older Japanese maintained healthy functional capacity over time. Although we could not follow those who dropped out during the observation period, this study provided useful evidence that socioeconomic disparities in functional health converge with age. Our findings inform the design of health policies and interventions aiming to maintain functional health among older adults with diverse socioeconomic backgrounds. In particular, public policies aiming to reduce socioeconomic disparities should be emphasized to promote healthy aging.