Background
The past decade of armed conflict in Afghanistan and Iraq has been associated with increased rates of suicidal behaviour, including suicidal ideation, plans, and attempts, in US military personnel. [
1‐
6] Findings from other nations have been less dramatic—perhaps related to smaller military populations hence greater difficulty detecting significant trends for rare events like suicide—but Canada, at least, may now be seeing similar patterns. [
7] Several studies have pointed to a greater risk of suicidality in modern veterans—a finding not detected in veterans of earlier conflicts. [
7‐
9]
The role of combat-related psychiatric disorders in rising military suicide rates has not been clear-cut. [
10] Although conditions which can emanate from trauma exposure, such as combat-related Posttraumatic Stress Disorder (PTSD), [
11] Major Depressive Disorder (MDD) [
12‐
15] and various anxiety disorders, [
16‐
18] each independently predict suicidal behaviour, several studies have shown little or no significant relationship between deployment and completed suicide. [
2] Therefore, it is important to examine other potential drivers of suicidal behaviour.
Insomnia is a prevalent problem among military cohorts both during and following deployment [
19,
20], and has been linked to suicidal ideation (SI), attempts, and completed suicide in both military and civilian populations [
2,
21‐
30]. Data obtained from the Deployment Life Study [
31] demonstrated that nearly half of their sample (48.6%) exceeded the clinically significant threshold for sleep problems [
32]. There are also a number of compelling reasons why insomnia may contribute to suicidal behaviour [
33]. For example, Bernert and Joiner report that poor sleep quality, via frightening dream content and insomnia, can disrupt within-sleep mood regulation processes. This in turn can impart a negative and potentially long-lasting effect on psychopathology, and may influence the association between sleep and suicidality [23]. Insomnia has also been shown to desensitise the serotonergic (1A) receptor system in rats [
34], and a number of studies have linked serotonergic deregulation with past suicidal attempts, future suicide prediction, and completed suicide [
23]. Thus, insomnia may play a prominent role in the formation of suicidal behaviour, and presents as a potential target for interventions aimed at preventing suicide.
A challenge in understanding the association between insomnia and suicidal behaviour is that sleep problems are core symptoms of common psychiatric disorders including MDD, PTSD, and Generalized Anxiety Disorder (GAD) [
35,
36]. Thus, it remains unclear whether the effect of insomnia on suicidal behaviours is better accounted for by the presence of psychiatric conditions that may include insomnia as a marker of symptom severity. Consequentially, it is important to examine the independent influence insomnia confers onto risk of suicidal behaviours by controlling for the psychiatric conditions.
Studies controlling for the presence of psychiatric conditions while examining the association between insomnia and risk of suicidal behaviours have yielded mixed results. One potential explanation for discrepant findings is that the relationship between insomnia and suicidality is moderated by mental health problems. Accordingly, the effect of insomnia on suicidality may differ among those with, compared to those without, a mental disorder.
While past studies have statistically controlled for the effect of psychopathology, no studies, especially in military samples, have examined the interactive link between insomnia and mental health status in predicting suicidal ideation. Better understanding such effect modification may help explain the discrepant findings and aid in identifying individuals for which sleep-oriented interventions might attenuate risk of suicidal behaviours. For example, Bernert and colleagues [
22] and Liu [
37] noted that although experiencing nightmares was significantly related to elevated suicidal symptoms, the relationship between insomnia and suicidality failed to reach significance. In a treatment-seeking sample of predominantly veterans, Richardson and colleagues [
38] failed to find significant associations between either insomnia or nightmares and SI when controlling for probable diagnoses of PTSD, MDD, GAD, or alcohol use disorder (AUD). Instead, MDD emerged as the only significant predictor of SI. Similarly, Bryan and colleagues
43 found that insomnia severity was not directly associated with concurrent or prospective suicidal ideation in three military samples when adjusting for depression.
Conversely, others have found an association between symptoms of insomnia and suicidal behaviour that remained significant after controlling for common psychiatric conditions [
39‐
41]. Specific to military populations, Ribeiro and colleagues [
25] found that insomnia symptoms predicted SI even after controlling for depression, hopelessness, PTSD, anxiety, and alcohol abuse. Pigeon and colleagues [
42] also demonstrated that veterans’ time to completed suicide was associated with sleep disturbances after adjusting for mental health, age, and substance-use symptoms.
Given a recent increase in reported rates of suicide among military members, [
1‐
6,
43] coupled with the few studies on insomnia and suicide in military members as opposed to other populations currently available, the authors of the current study hypothesize that insomnia does contribute to SI amongst military personnel, and that an interactive effect between insomnia and mental health conditions such as PTSD may exist.. The current paper used data from a 2013 population-based mental health survey of serving Canadian military personnel to explore: 1) The contribution of insomnia towards SI while controlling for common mental disorders; and 2) The possibility of interactions between insomnia and mental disorders with respect to SI.
Discussion
Consistent with previous research in military samples, results indicated that insomnia is commonly reported among service members. [
19,
20] As expected, from the univariate models the psychiatric disorders (PTSD, MDD, GAD, PD and AUD), as well as insomnia, each predicted SI on their own. However, these models do not account for the overlapping variance that is shared between disorders. Further, insomnia cumulatively increased the odds of SI, such that insomnia severity was associated with an increased likelihood of reporting of SI.
A number of novel findings emerged regarding number of mental health diagnoses. First, a cumulative effect was demonstrated such that the odds of experiencing SI increased with additional mental health diagnoses, indicating the potential for a dose-response relationship between mental illness and risk of SI. Mental health diagnosis also conferred a moderating effect such that insomnia incrementally increased the odds of SI, but only among those with no or one mental health diagnosis present. Conversely, no significant cumulative effect emerged between insomnia and SI for respondents with two or more mental health diagnoses. The findings suggest there may be a ceiling effect on the relative impact of insomnia on suicidal ideation above and beyond the effect of comorbid mental health disorders. Therefore, when comorbidity is present, the influence of insomnia on SI is minimized due to already-existing mental health symptoms affecting the formation and maintenance of suicidal behaviour. Alternatively, it may be that when the frequency and/or severity of mental health symptoms is relatively low, incremental increases in sleep disturbances may be perceived as increasingly pervasive and burdensome to well-being.
The current study found that approximately 41% of the sample reported experiencing insomnia some, most, or all of the time. This approximates the rate of sleep problems reported in the Deployment Life Study (48.6%) [
32], but is noticeably higher than the reported rates of insomnia (16–21%, as measured by frequency) in several general population samples, according to an epidemiologic review by Ohayon [
49] and marginally higher than the rates averaged across adult general populations (30–36%) by Morin and Jarrin [
50]. These findings suggest that military personnel may be at increased risk of insomnia compared to their civilian counterparts, and may benefit from additional screening and intervention targeting insomnia. Additionally, the current study found that approximately 10% of the sample met screening criteria for one mental health disorder and an additional 6% met screening criteria for two or more. While estimates of mental health disorder prevalence among military personnel range widely, this finding is similar to that of Hoge and colleagues, which found that 11.3% of military personnel deployed to Afghanistan as part of Operation Enduring Freedom screened positively for a mental health disorder [
51]. These rates are lower than that of the American general population (26.2% for any past-year DSM-IV disorder,) as reported by Kessler and colleagues [
52]. This discrepancy may be, at least in part, attributable to the “healthy soldier” effect. Finally, the current study found that 4.3% of participants reported past-year SI. A nationally-representative study of the Canadian general population found a past-year SI rate of approximately 3.3% [
53], while data from the US military’s Post-Deployment Health Assessment survey found that 1.3% of participants reported “some” to “a lot” of SI [
51]. Similarly to mental health disorders, SI may be susceptible to underreporting in actively serving military populations for a number of reasons (“healthy soldier” effect, fears about job security, stigma, etc.). The incongruity between the rate reported in the current study and Hoge and colleagues is interesting; further research pertaining to SI and its management among national armies may help elucidate important differences affecting these rates.
The current study gives rise to important clinical implications. Foremost, sleep-oriented interventions may attenuate risk of suicidal behaviours, particularly amongst military personnel experiencing insomnia independently of mental health comorbidities. For those with mental health conditions, studies documenting the persistence of insomnia despite treatment for conditions such as MDD [
54] and PTSD [
55] suggest sleep problems that co-occur with psychiatric conditions may not resolve themselves as a result of treatments targeting specific mental health diagnoses. Thus, treatments adapted to complement other interventions are advisable. For example, the following may help to reduce risk of SI: inclusion of psychoeducation related to sleep disturbances and PTSD, psychotherapy to target nightmares, such as nightmare rescripting or imagery rehearsal therapy [
56,
57], cognitive-behavioural therapy for insomnia [
58], use of pharmacotherapy such as prazosin for trauma related nightmares [
59‐
61] or risperidone [
62], or low-dose sedating antidepressants or hypnotics [
63‐
65]. These treatments may provide additional gains and increased quality of life among individuals struggling with sleep problems and mental disorders.
Although the current study has several strengths, including the use of a nationally- representative Canadian military sample that includes individuals deployed to the recent conflict in Afghanistan, its limitations are worth noting. Although “trouble going to sleep or staying asleep” was part of questionnaire inferred to assess current health problems, no time frame was specified. Thus, we cannot guarantee that mental health conditions and insomnia occurred at the same time participants experienced SI. We also used single items to measure suicidality and insomnia. While not ideal, a similar single-item measures have been used elsewhere to study insomnia and suicide [
38]; however, the use of more elaborate measures of insomnia and SI in future studies may further clarify the relationship between insomnia, mental health conditions, and SI identified in the current study. Additionally, the item used to measure insomnia was worded to include both problems falling or staying asleep as a single item. It is possible that differences exist between those who endorse difficulty falling asleep vs. those who experience problems staying asleep, and that individuals who report difficulty both falling and staying asleep differ from those who experience difficulty either falling
or staying asleep.
It is also worthwhile noting that SI is distinct from other suicidal behavior, such as engaging in self-harm, and suicide planning or attempts. Importantly, while the rate of SI in the current study was higher than that of a similar US military population, this does not necessarily mean Canadian soldiers are at a greater risk of suicidal behaviors than their American counterparts. Further studies assessing a range of suicidal behaviors are recommended in order to better understand the implications of this finding. We were also unable to examine the effect of specific mental health conditions (i.e., PTSD, MDD, GAD, PD and AUD) due to a limited number of respondents reporting each disorder. Further, the large number of mental disorders we assessed made it impractical to test individually for single-disorder interactions. The cross-sectional design also limited our ability to evaluate causal relationships between insomnia, psychiatric conditions, and SI. Further, the current findings are limited to actively serving military members, and cannot be generalized to other psychiatric or veteran populations. Lastly, the self-report nature of the data means we must consider the possibility of underreporting symptoms of mental health conditions and SI, given the nature of the study population.
Further research regarding the effectiveness of sleep-related treatments to reduce SI in military members is certainly warranted. Longitudinal research may provide insight into potential causal pathways between variables examined in the current study, both in the development of these conditions and their treatment. Given the low base rates of suicide completions and attempts, future studies should also consider collecting data from a sample in which these rates are higher in order to evaluate whether the same factors that contribute to increased risk for SI also contributes to increased risk for suicide completions and attempts, such as the Army Study to Assess Risk and Resilience in Service members (Army STARRS) studies [
5,
66]. Although the current study examined the risk of mental-health diagnosis categorically, further research will benefit from investigating whether certain diagnoses confer greater risk or burden than others. Finally, research targeting military clinical samples with specific psychiatric disorders is needed to test whether the independent risk of SI associated with insomnia is consistent when controlling for the influence of each mental health disorder separately.
Acknowledgments
Not applicable.