Clinical reviewThe insomnia and suicide link: toward an enhanced understanding of this relationship
Introduction
Insomnia is a major public health concern. Rates of insomnia in the general population are between 10 and 15% [1], [2], [3], with approximately 30% of the population suffering from insomnia symptoms at any given moment [1]. Insomnia negatively impacts mental health, quality of life, occupational and psychosocial functioning, and is associated with considerable economic costs [4], [5], [6]. In addition, recent research has highlighted a greater risk for suicide in people with insomnia compared to those without insomnia [e.g., ∗[7], ∗[8]]. Despite the association of insomnia with psychiatric illnesses [9] that predict suicide risk [10], several empirical studies [e.g., ∗[7], [11], [12]] and a meta-analysis [8] suggest that the relationship between insomnia and suicide risk is unique. Review papers also suggest that insomnia, as well as other sleep disturbances (e.g., nightmares), is associated with suicide-related thoughts and behaviors [13], [14], [15].
Suicide is well recognized as a leading cause of death worldwide. In the United States alone, a recent report indicated a rate of 12.1 suicides per 100,000 people [16]. This rate is particularly alarming because suicides reflect only a small percentage of all non-fatal suicide-related thoughts and behaviors [17], [18]. There is an urgent need to further the understanding of suicide risk factors, particularly those that can be targeted and modified through intervention and are independent of psychiatric illness. The majority of suicide risk research is conducted in psychiatric samples, which is not surprising given that over 90% of people who commit suicide have psychiatric illness [10], [19]; however, other suicide risk factors (including insomnia) are present in the general population. Identifying insomnia as an independent, modifiable risk factor for suicide thus has critical implications for suicide prevention and intervention efforts.
Considerable evidence supports a relationship between insomnia and suicide [8]; yet there remains a strong need to further our understanding of this relationship beyond its mere existence. The extant research may be limited by inconsistent definitions and measurements of insomnia across studies. Though this issue was raised over a decade ago [20], it remains a problem. Similar issues hinder research on suicide-related thoughts and behaviors [21]. Moreover, there is a deficit of empirical research focused on identifying mediating mechanisms of the insomnia-suicide relationship [22]. Researchers have suggested potential mediators in the context of other study findings [e.g., ∗[7], [12]], yet a thorough understanding of these variables in relation to both insomnia and suicide has not been made explicit. Without an enhanced understanding of the insomnia-suicide relationship, identifying people who are at risk of suicide by virtue of having insomnia is difficult.
To date, no review paper has focused on evaluating the link between suicide risk and insomnia as a specific sleep disturbance. The distinctiveness of sleep disturbance types and associated treatments justifies a need to independently evaluate each in relation to suicide risk. Given the critical implications of an insomnia-suicide link and the high prevalence of insomnia in the general population, the current paper is a call to arms for researchers to develop the next phase of this study. Accordingly, this paper presents an up-to-date review of the existing literature, and proposes two fundamental objectives for future research that address the limitations to date: 1) improve the inconsistent classifications of insomnia and suicide-related thoughts and behaviors across studies; and 2) identify specific mechanisms of the insomnia-suicide relationship by testing the hypotheses put forth in this review. Once these objectives are attained, the efficacy of insomnia interventions for reducing suicide risk can be more adequately evaluated. Cognitive behavioral therapy for insomnia (CBT-I) is of particular interest, given that various proposed mechanisms of the insomnia-suicide relationship are targeted by components of CBT-I. Before consideration of future research, we first turn our attention to the state of the current literature.
Section snippets
Search criteria
The insomnia and suicide literature to-date consists of studies with various designs (longitudinal, cross-sectional), classifications of insomnia (nighttime symptoms only, nighttime symptoms plus daytime dysfunction, poor sleep quality, insomnia diagnosis), insomnia assessment techniques (retrospective recall, daily sleep monitoring) and suicide outcome measures (ideation, attempts, suicide). Thorough searches of PsycINFO and PubMed were conducted using the terms insomnia, sleep, sleep
Inconsistency and challenges within insomnia literature
Inconsistent classifications and measurements of insomnia and suicide variables is one important issue that currently hinders understanding in the insomnia-suicide literature [20]. The term insomnia is used to denote both a symptom and a disorder [74]. In fact, several insomnia categories are well recognized across studies: sleep-specific symptoms regardless of duration or consequence; sleep-specific symptoms accompanied by daytime consequences; dissatisfaction with sleep quality or quantity;
Potential mediators of the insomnia and suicide relationship
This paper is not the first call for research into mediators of the insomnia-suicide relationship [22]. If there is, in fact, a unique relationship between insomnia and suicide risk, then understanding the mechanisms or processes that underlie this relationship is important for developing effective interventions. Rather than hypothesizing a direct causal relationship between a diagnosis (or symptoms) of insomnia and suicide risk, it can be hypothesized that insomnia precedes another mechanism,
Conclusions and future research directions
Given the current rates of suicide-related behaviors, there is a dire need to identify and understand additional factors that increase the risk of these behaviors. With this understanding, treatments will be improved and suicide rates will subsequently decline. This paper provided an updated review of the literature linking insomnia to suicide, and considered the next phase of study to improve our understanding of this link with the ultimate goal of evaluating insomnia treatments as a means to
Acknowledgments
We gratefully acknowledge Emma MacDonald for her invaluable feedback on this manuscript. There are no conflicts of interest to report.
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