Psychological stress and sleep influence each other in a complex and bidirectional manner.1 It is well-recognized that behavioral health disorders impair sleep, sleep quality, and associated features such as cognition.2 A complaint of poor sleep, particularly insomnia, is an essential criterion for many psychiatric illnesses. In short, these conditions are thought to cause insomnia. What is less well established is how poor sleep can cause, or at least contribute to, the development of behavioral health disorders. Acute and chronic life stressors commonly diminish sleep quality and impair sleep onset. In turn, a lack of restorative sleep (insufficient quality or quantity) can reduce physical and emotional resiliency, leading to a maladaptive stress response, putatively increasing the chance of developing anxiety or depression.
In this issue of the Journal of Clinical Sleep Medicine, Palagini and colleagues provide an important addition to the literature, demonstrating that resilience is negatively correlated with insomnia.3 In their study, the authors refer to the stress diathesis model and the stress-risk-vulnerability dimension. According to the diathesis-stress model of insomnia, patients with insomnia experience high stress-related sleep reactivity and greater emotional dysregulation. The stress-risk-vulnerability dimension describes an individual's dynamic capacity to process and adapt to stressors while maintaining normal psychological and physical functioning. In short, this process describes an individual's resilience. Those with less resilience have a diminished capacity to successfully adapt to stressful events and have an increased vulnerability for developing insomnia (and by extension, mental health disorders). In the study by Palagini et al., because individuals with insomnia had heightened stress-related sleep reactivity, more emotional dys-regulation, and hyperarousal, they also had reduced measures of resilience.
The concept that sleep disturbances may not be merely a product of an individual's ability to tolerate stress and anxiety, but may actually cause or contribute to maladaptive coping and dysfunctional processing, has been previously hypothesized. Data supporting the argument for sleep as a determinant of psychological resiliency include studies assessing the impact of sleep quality immediately preceding trauma,4 as well as studies demonstrating the role of sleep as a function of suicide risk in vulnerable patients.5,6 A study exploring the relationship between perceived sleep quality and resilience found those reporting poor sleep quality (Pittsburgh Sleep Quality Index scores > 5) obtained lower resilience scores compared with those reporting good sleep quality (P = .025).7 In this study, those with poorer sleep quality (odds ratio = 3.3) and those sleeping < 7 h/night (odds ratio = 3.3), were at greater risk of low resilience. In a study determining the relationships between sleep, indices of resilience, and behavior among children, investigators found sleep disturbances reduced resilience and consequently increased problematic behavior, potentially predisposing individuals to psychopathology.8 Similarly, Wong and colleagues observed that sleep rhythmicity during early childhood predicted behavioral control in adolescence and resilience as young adults.9
Much of the work exploring preexisting sleep disorders and susceptibility to future psychiatric conditions has been done in posttraumatic stress disorder (PTSD). An evolving body of literature supports the view that sleep disorders may be implicated in the underlying pathophysiology of PTSD and not simply a consequence or manifestation of the disease.10,11 In our practice, we have seen many Military service members returning from combat with sleep complaints and sleep disorders, particularly insufficient sleep syndrome, obstructive sleep apnea, and insomnia. We have observed those with sleep complaints or diagnosed sleep disorders have substantially higher rates of PTSD compared to those without sleep issues.12,13 This is especially true of those who did not sustain physical combat injuries. After excluding individuals with traumatic injuries, premorbid sleep complaints were significantly higher among those who developed PTSD compared with controls. We hypothesized that patients with existing disrupted sleep may have diminished resiliency making them more vulnerable to developing behavioral health issues and increasing their risk of subsequent PTSD.
In the study by Palagini et al., it should be noted that the authors are largely working within the construct that resilience capacity is more of a static trait. Similar to work by Tkachenko and Dinges, there may be distinct cognitive profiles modulating the stress response, leading to a differential vulnerability to effects of sleep loss.14 The impact that sleep debt has on resiliency, the stress response and an individual's ability to appropriately process stress, therefore, may be at least partially genetically predisposed. To state that resilience capacity is unchangeable, though, may be an oversimplification. More likely, there is a dynamic and interdependent relationship where resiliency has a biologic tendency but is modulated by environmental factors to include sleep. Regardless, their work gives further evidence that sleep quality and resiliency are linked. Given that resilience is a critical process for processing events and adaptively overcoming stress, it seems clear that poor sleep would predis-pose to conditions arising from maladaptive stress processing. The authors accurately acknowledge that the data are limited to subjective reports, and the cross-sectional design provides little information regarding the natural history of the insomnia.
Because this was only one snapshot in time, it is unclear how resiliency was affected by the presence or severity of insomnia, or whether treatment of insomnia would improve resiliency. Despite these limitations, the impact of lowered resilience is supportive of the hypothesis that preexisting insomnia might increase the risk of disorders such as PTSD. We concur that the evaluation and treatment of emotional dysregulation should be a routine component of sleep medicine practice, but clearly more work is indicated in order to definitively prove causation. Regardless, this manuscript sets the stage for a longitudinal study to determine whether diminished resiliency is a trait that lowers the threshold to develop insomnia, whether insomnia is a condition that can itself diminish resiliency, or whether there is a true bidirectional relationship that perpetuates the vicious cycle of worsening symptoms.
The authors report no conflicts of interest. The views in this commentary reflect those of the authors, and do not constitute official policy of the United States Army or Department of Defense.
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