Objectives: The purpose of this study was to examine the epidemiological features of self-injury in Japan, and to investigate the factors associated with a history of self-injury, using nationwide random sample data on Japan in 2010.
Methods: Questionnaires were distributed to 2,693 subjects, aged 16-49 years, randomly selected from the all over Japan using 2-stage stratified random sampling; the answers regarding self-injury were analyzed. Potential risk factors were compared between those who answered that they had a history of self-injury (self-injury group) and those who answered that they did not (non-self-injury group).
Results: Responses were obtained from 1,540 participants (response rate, 57.2%). Lifetime prevalence of having 1 or more self-injury events was 7.1% overall (3.9% for men; 9.5% for women) and approximately half of them reported a repetitive history of self-injury. Lifetime prevalence of self-injury was highest in those aged 16-29 years (9.9%, 16-29 years; 5.6%, 30-39 years; 5.7%, 40-49 years). Lifetime prevalence among women (16-29 years, 30-39 years, and 40-49 years) decreased with age (15.7%, 7.5%, and 5.8%, respectively), however, that among men increased with age (3.0%, 3.4%, and 5.5%, respectively). Compared with the non-self-injury group, those in the self-injury group were significantly more likely to have a history of cigarette smoking (self-injury group, 47.5%; non-self-injury group, 28.2%; adjusted odds ratio [95% confidence interval]: 2.18 [1.32-3.58]), childhood abuse (23.6% and 3.7%, respectively, 4.24 [2.18-8.25]), induced abortion (30.3% and 12.7%, respectively, 1.93[1.13-3.30]); moreover, they were significantly less likely to answer that they had a happy life when they were junior high school students (41.1% and 78.6%, respectively, 0.45 [0.25-0.79]). In addition, those in the self-injury group were more likely to report a history of parental divorce, that they did not have good communication with their parents, and that they did not have respect and appreciation for their parents; however, these factors were not significant after adjustment.
Conclusion: These results are consistent with those of previous research reports in which the lifetime prevalence of self-injury was high among women aged 16-29 years, and in which self-injury was more likely to occur among individuals who had a history of cigarette smoking and childhood abuse. Such individuals should be provided care to prevent self-injury. In addition, from a social point of view, research examining family environments including these factors is required.