With regard to major depressive disorder, almost all patients present with sleep disturbances and altered circadian rhythms including hormonal secretion, cardiac function, and body temperature. Sleep disruption is a major symptom in depression, with over 90% of patients showing sleep complaints that affect daytime functioning (Thase, 1999). Insomnia often appears before the onset of mood disorder symptoms and may persist into clinical remission: sleep disturbances are known to be a frequent residual symptom of depression, and the presence of insomnia marks an increased risk of relapse or recurrence. Sleep difficulties often are the key factor that causes depressed patients to seek medical help, and relief of sleep disturbances is important to encourage compliance with antidepressant medication. Associated with chronic depression, sleep disturbance can have as great an impact on health-related quality of life as the mental illness itself (Katz & McHorney, 2002).
It is well known that changes in clinical state are accompanied by shifts in timing of the sleep-wake cycle. The switch out of depression is often associated with a spontaneous sleep deprivation. Conversely, a prescribed sleep deprivation can rapidly show antidepressive activity. Even more strikingly, a phase advance of sleep timing can induce longer-lasting antidepressant effects, suggesting an intimate functional relationship between sleep, its timing, and the depressive state.
In healthy individuals and in patients with affective disorders, there is a close link between circadian rhyt
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European College of Neuropsychopharmacology