Factors Regarding Suicide Decline in Japan: A Longitudinal Study on Psychiatric Diagnosis of Serious Suicide Attempters

Abstract

Background:The number of suicides in Japan decreased during the period from 2012 through 2019. Because data on factors associated with this decline are limited, we conducted a retrospective longitudinal study of psychiatric diagnoses of serious suicide attempters before 2012 and after 2019.Methods: Serious suicide attempters admitted to the critical care medicine (CCM) department of Nippon Medical School Hospital between 2006 and 2017 were included and classified as those before and after the suicide decline in 2012. Chi-square test and residual analysis were used to analyze changes in the proportion of suicide attempters among all patients admitted to CCM and to examine differences in the proportion of psychiatric diagnoses. Results:The proportion of suicide attempters among CCM hospitalized patients decreased overall (χ 2 (1) =18.29, p<.01). The proportion of psychiatric diagnoses changed significantly (χ 2 (8)=62.21, p<0.001); specifically, it decreased for schizophrenia (residual: −2.28), depressive disorders (residual: −5.39), persistent mood disorders (residual: −3.58), and reaction to stress disorders (residual: −2.73). Depressive disorders decreased and had a large contribution ratio in both sexes. Conclusions:The decrease in the proportion of attempted suicides among patients admitted to CCM was consistent with the decline in suicides in Japan. Analysis by psychiatric diagnosis confirmed a significant decrease in the proportion of suicide attempts associated with depressive disorders, schizophrenia, and reaction to stress disorders, which were the most common disorders associated with attempted suicide. Depressive disorders made the greatest contribution to the reduction in suicide attempts.