Original ArticleSuicide risk among individuals with sleep disturbances in Japan: a case–control psychological autopsy study
Introduction
Suicide is a major global health concern. The World Health Organization estimates that approximately one million people die by suicide every year. Japan’s annual suicide rate is the highest of the seven major industrialized nations [1] and dramatically increased in 1998; since then, more than 30,000 individuals have died annually by suicide through 2011 [2]. Factors that increase risk of suicide and suicidal behaviors include mental disorders [3], [4], physical disease [5], [6], [7], unemployment [8], [9], [10], [11], adverse working conditions [10], divorce [11], [12], childhood maltreatment [13], [14], [15], and family history of suicidal behavior [15].
Sleep disturbances may also represent a critical risk factor for suicide, and the early detection and treatment may greatly contribute to suicide prevention. A previous meta-analysis reported significant associations between sleep disturbances and suicidal thoughts and behaviors [16]. A Norwegian population-based study reported that age- and sex-adjusted hazard ratios for suicide among individuals with sleep disturbances ranged from 1.9 to 4.3, depending on the frequency [17]. Sleep disturbances that increased suicide risk included insomnia [18], [19], [20], [21], [22], [23], nightmares [22], [24], [25], [26], [27], [28], difficulty initiating sleep [29], and difficulty maintaining sleep [30]. Short sleep duration was also significantly associated with suicide risk [28], [31], [32], [33]. The association was not explained by mental disorders; rather, it was independent of mental disorders [16], [17], [29], [31], [34]. Although previous studies have consistently shown an association between sleep disturbances and suicide, the usefulness of sleep disturbance assessment as a marker of suicide, compared to mental disorders, has not been clearly evaluated, and no quantitative measures, such as population attributable risk proportion (PARP) and estimated post-screening probability of suicide, have been provided.
In addition, the relationships between sleep disturbances, mental disorders, and suicide may differ by culture and country. Limited data are available regarding the relationship between sleep disturbances and suicide in Japan. Only a prospective cohort study of 13,259 middle-aged adults indicated that difficulty maintaining sleep increased risk of suicide [30]. As for suicidal tendencies, there were significant associations between feelings of insufficient sleep and suicide ideation among middle-aged female [35] and male workers [36]. Insomnia and overall sleep disorders were also significantly associated with increased risk of suicide ideation among psychosomatic clinic outpatients [37]. These findings suggest that sleep disturbances are also a risk factor for suicide in Japan. However, sleep time in Japan is the second shortest in the world after Korea [38], and the prevalence of mental disorders tends to be lower in Asian countries, including Japan, compared to Western countries [39]. These country-dependent differences may influence the impact that sleep disturbances or mental disorders have on suicide prevention.
In the present study, we analyzed data from the first Japanese case–control psychological autopsy study [40] to assess the association between sleep disturbances and suicide in Japan, after adjusting for mental disorders including depression. To verify a comparable impact of sleep disturbances in suicide prevention, we also calculated a PARP of suicide associated with sleep disturbances, as well as mental disorders, and also simulated posterior probabilities of suicide among screening positives for populations with different risks of suicide when sleep disturbance assessment was used in a screening of suicide.
Section snippets
Study participants
The study included 52 individuals over 20 years of age who died by suicide in various areas of Japan. Bereaved family members who visited prefectural Mental Health Welfare Centers for individual support or survivor meetings were asked to participate at the time of visit. Suicide case respondents represented various areas of Japan. The surveys, described below, took place from January 2007 to July 2009. The mean period from incidence of suicide to administration of the survey was 17.4 months (SD,
Demographics and suicide-related characteristics
Table 1 presents demographics for the suicide and control groups. The proportion of junior high school graduates (11 years of education or less) was higher for the suicide cases than the controls. The suicide group also included more individuals who had not been married and had a lower employment rate than the control group.
Association between sleep disturbances and suicide
Sleep disturbances, experienced by 75.5% of suicide cases and 11.0% of controls, were significantly associated with suicide (OR = 21.6, 95% CI = 7.6–61.5, p < 0.001) (Table 2). Of
Discussion
The analysis of data from the Japanese case–control psychological autopsy study confirmed that there is a significant association between sleep disturbances and suicide in the Japanese population. Suicide risk in people with sleep disturbances was estimated to be 21.6 times higher compared to those without sleep disturbances, and remained high even after adjustment for depressive or any mental disorders (9.7 times higher when adjusted for depressive disorders; 12.7 times higher for any mental
Limitations
There were several limitations to the present study. First, the sample size was relatively small, and differences among subgroups such as gender and age could not be explored. Second, the non-randomized sampling of suicide cases was possibly biased. Cases were selected using relatives who sought help from prefectural Mental Health and Welfare Centers or participated in survivor support programs. Suicide completers who had lived alone were thus not included. In addition, the response rate for
Conflict of interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2013.11.789.
Acknowledgements
We thank the bereaved families, controls, and their families for their participation in our study. We also thank the investigators from local government agencies and Central Research Services, Inc. for their assistance in collecting valuable data. Funding of this study was provided by Scientific Research H19,H20,H21-KOKORO-Japan 007, a Grants-in-aid from the Ministry of Health, Labour and Welfare in Japan.
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