Prefecture-level economic conditions and risk of suicide in Japan: A repeated cross-sectional analysis 1975-2010

Background: Geographical inequalities in suicide have risen dramatically across 47 prefectures in Japan since 1995. We sought to examine temporal changes in the associations between prefecture-level economic conditions and completed suicide during the recent 35 years, controlling for individual composition in each prefecture. Methods: Based on quinquennial vital statistics and census data from 1975 to 2010, we analysed the entire population aged 25-64 years. The total number of suicides was 87 553 men and 34 559 women. As indicators of prefecture-level economic conditions, we used average yearly income, average savings and income inequality (measured by Gini coefficients for yearly income). For each sex, we estimated odds ratios and 95% credible intervals for suicide using multilevel logistic regression models, with cells at level 1, years at level 2 and prefectures at level 3. Results: Even after adjusting for individual age, occupation and time trends, low average savings at prefecture level were associated with a higher risk of suicide among men (odds ratio in low vs. high savings: 1.13, 95% credible interval: 1.05-1.21), whereas no clear patterns were observed with other economic indicators. When we further examined the associations in year-specific models by conducting a two-level analysis, both average yearly income and average savings were inversely associated with suicide risk in recent years. No clear association was found between income inequality and suicide risk for either sex. Conclusion: The present findings suggest that low area socioeconomic status may be driving the growing geographical inequalities in suicide in Japan, primarily among men.