Long-term annual trends in suicide rates and characteristics of suicide cases in prisons in Japan

This study aims to investigate suicide mortality rates and their time trends in prisons against the national level and related facilities, and to identify characteristics of suicide cases in Japan. The study design of this study was a nationwide cross-sectional study. It targeted prisoners and individuals incarcerated in all facilities, such as prisons, under the control of Ministry of Justice in Japan. The suicide rate (per 100,000) was calculated, and its annual trend described. The number and percentage of individuals by each measure were described in suicide cases. The suicide rate from 1952 to 2022 showed considerable annual variation (minimum 5.5 to maximum 46.8). No clear parallel trend was visually observed with the year trends in suicide rates for the Japanese population, male, or female. There were 184 suicides from 2010 to 2020. The sex was 89% male and 10% female. The age distribution showed the largest groups were those in their 30 s (26%) and 40 s (34%). The suicide rate in Japan was not found to be as high as in other developed countries. The trends in annual suicide rates differed significantly, and an unclear correlation was observed with the suicide rate in all of Japan. Suicides among middle-aged men were high. The information on suicide and for prevention was so limited, and further research is needed.