Comparing the incidence rates of dementia: Association of social participation among older adults in Japan

Social participation is associated with reduced dementia risk and has recently increased in Japan, which may be related to changes in dementia incidence rates. This study compared dementia incidence rates between two cohorts of older Japanese adults across five municipalities and examined whether differences were associated with social participation or social participation-related variables. We analyzed data from the Japan Gerontological Evaluation Study, comprising two three-year follow-up cohorts (2013-2016: n = 25,281; 2016-2019: n = 26,284) of community-dwelling adults aged ≥ 65 years not certified for long-term care. Survival analysis was performed to calculate hazard ratios for dementia, using cohort and social participation as explanatory variables. Analyses were stratified by age (65-74 and ≥ 75 years) and adjusted for demographics, social participation, and social participation-related variables. Dementia incidence declined from 149.7 to 131.3 per 10,000 person-years between cohorts. The sex- and age-adjusted hazard ratios for the 2016-2019 cohort (reference: 2013-2016) were 0.83 (95 % CI: 0.67, 1.03) for ages 65-74 and 0.83 (95 % CI: 0.75, 0.91) for ≥ 75 years. After adjusting for social participation and social participation-related variables, the cohort difference became non-significant in the ≥ 75 years group (hazard ratio: 0.99; 95 % CI: 0.89, 1.09). This decline in dementia incidence rates among those aged ≥ 75 years may be associated with social participation and related variables. These findings suggest a potential association between social participation and lower dementia incidence rates; however, further research is needed to confirm these results.