Objectives In this study, we aim to clarify the optimal threshold for the frequency of volunteer group participation among older people aged 65 years and above, which is expected to prevent the risk of developing depression.Methods We utilized longitudinal data from 2013 to 2016, collated by the Japan Gerontological Evaluation Study for people aged ≥65 years living in 24 municipalities and not certified as requiring long-term care. In addition, those who were not depressed in 2013 (≥5 points on the Geriatric Depression Scale-15) were followed up for 3 years and classified according to the frequency of participation in the volunteer group in 2013 (≥once per year, ≥once per month, ≥once per week). The odds ratio (OR) of being newly depressed in 2016 was determined using the propensity score matching method and t-test.Results The frequency of volunteer group participation for 9,722 (25.0%), 6,026 (15.5%), and 2,735 (7.0%) older individuals was≥once per year, once per month, and once per week, respectively. A comparison of the balanced attributes of the volunteer group participation with those of the non-participation group using propensity scores revealed that the risk of developing depressive symptoms was significantly lower in the former compared with the latter for the frequency of ≥once per month and OR of 0.82 (95% confidence interval: 0.72, 0.93). The ORs were 0.92 (0.83, 1.02) and 0.82 (0.68, 1.00) for the ≥once per year and once per week groups, respectively.Conclusion Older people's participation in a volunteer group ≥once per month was effective in reducing the risk of developing depressive symptoms after 3 years. This suggests that increasing the opportunities and community places where older people can be involved as volunteers even once a month may be employed as an effective measure to prevent depression.
Keywords: community development; long-term care prevention; prevention of depressive symptoms; social participation.