Although the important role of social support in mental health is acknowledged, no prospective study has yet examined the relation of social support to suicide. Here, we investigated the association between social support and suicide in a cohort of Japanese men and women. A total of 26,672 men and 29,865 women aged 40-69 years enrolled in the Japan Public Health Center-based prospective study in 1993-1994 completed a self-administered questionnaire which included four items of social support, and were followed for death through December 2005. Hazard ratios (HRs) and 95% confidence intervals (95% CI) of suicidal death by social support index were estimated using a Cox proportional hazards regression model. A total of 180 suicidal deaths were recorded during an average of 12 years' follow-up. Men and women with the highest level of social support had a significantly decreased risk of suicide, with HRs (95% CI) for the highest versus lowest social support group of 0.56 (0.33-0.94) and 0.38 (0.16-0.89) in men and women, respectively. Esteem support and having four or more friends were associated with a lower risk of suicide in women [0.32 (0.13-0.77)] and in both sexes [men: 0.56 (0.36-0.88); women: 0.65 (0.32-1.30)], respectively, whereas confident support was not. These findings suggest that social support may be important for suicide prevention. Avoiding social isolation may decrease the incidence of suicide in men and women, and esteem support can provide additional benefit for women.
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