Education level and incident functional disability in elderly Japanese: The Ohsaki Cohort 2006 study

As the factors that link education level with incident functional disability in elderly Japanese have never been investigated, the present study investigated this issue in an elderly Japanese population. A 9-year prospective cohort study (2006-2015) was conducted among 8,680 Japanese individuals (≥65 years), Ohsaki city, Japan. In a baseline survey, we collected data on education level and potential mediators. Data on incident functional disability were retrieved from the Long-term Care Insurance database. The Cox proportional hazards model was used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) for incident functional disability by education level (below upper-secondary education (reference), and upper secondary education and above). Mediating effects were estimated using accelerated failure time model and a logistic regression model. During 9-year follow-up period, 2,742 cases (31.6%) of incident functional disability were observed, and education level showed an inverse association with functional disability (P for trend <0.01). Participation in community activities had the largest mediating effect (34.7%) on the relationship between education level and incident functional disability. This effect remained among those aged 65-74 years (19.9%) but became negligible among those aged ≥75 years. Other potential mediators (such as smoking and drinking status) were also tested, but these showed only small mediating effects. The inverse association between education level and the incident risk of functional disability appears to be largely mediated by participation in community activities among elderly Japanese, especially those aged 65-74 years.