Sleep disturbance affects 50% to 80% of all patients with mental disorders and it is currently a symptom of 19 axis I disorders
]. At the same time, it is considered to be a disorder in itself if the sleep disturbance impairs daily functioning
]. With this diagnostic multitude, there is a possibility that clinicians regard the sleep disturbance as an epiphenomenon that will be dissolved once the primary mental disorder is treated and not as a valid stand-alone clinical entity
]. This distinction can have consequences for choice of treatment for these patients
] and sleep disturbance is poorly recognized when patients have a mental disorder
The relationship between sleep and mental disorders is complex and not fully understood. Sleep disturbance may precede depression
], and 40% to 70% of patients who are successfully treated for depression experience sleep disturbance as a residual symptom
]. On the other hand, the remission rate following anti-depressive treatment can be doubled if adjunct treatment for sleep disturbance is provided
], and depression can be treated using cognitive behavior therapy for insomnia alone
]. These findings challenge the assumption that the sleep disturbance is secondary to a primary disorder. It may be better conceptualized as a comorbid condition, at least in depression. In a state-of-the-science statement the National Institutes of Health (NIH) recommended that when insomnia occurs concurrent with other disorders it should be considered comorbid rather than secondary
]. In the online draft for the DSM-5, this recommendation is taken into consideration and a paradigm shift is proposed as to how sleep disturbance should be conceptualized in patients with mental disorders
]. It is suggested that insomnia should always be coded if the criteria are fulfilled, regardless of meeting criteria for other disorders.
Most research so far on the association between sleep disturbance and mental disorders have been conducted in selected patient groups, mostly depressed patients, that may not fully resemble the heterogeneous group of patients found in public health care systems. The clinical usefulness of the NIH recommendation to regard insomnia as a comorbid disorder, rather than an epiphenomenon to a primary mental disorder, would be further supported if it was demonstrated that sleep disturbance is associated with distress and disability independently of the patients’ primary diagnosis also in settings representative of mental health care. Studies investigating such associations may be particularly relevant now with the advent of the DSM-5 proposal. However, no studies have been conducted to test if sleep disturbance is associated with current clinical state and benefit from treatment for patients representative of clinical settings. The aim of the current study was thus to test the hypothesis that sleep disturbance, independently of the patients’ primary mental disorder, is associated with variations in quality of life, disorder and symptom severity, level of functioning, and benefit from treatment in a large, heterogenous, clinical sample.