A sad day's night: The dynamic role of sleep in the context of major depression

Sleep disturbances are known to be a potential risk factor for the development and recurrence of depression. Still, sleep has remained under-acknowledged in depression treatment, probably because it is not well understood what the exact role of sleep is in depression in daily life. For this dissertation we captured the flow of daily life in which sleep- and depression-related factors develop and change to investigate the role of sleep within the participant’s natural environment. Our two studies regarding the sleep hormone melatonin showed large differences between and within individuals in the natural ebb and flow of melatonin. Abnormal patterns in melatonin secretion were not characteristic for being depressed. Interestingly, higher melatonin levels were associated with antidepressant intake in some individuals, and melatonin, mood, and fatigue seemed to be unassociated in severely depressed patients but not in other participants. The studies regarding behavior showed that changes in sleep were associated with next-day changes in mood and physical activity. Changes in sleep were associated with next-week changes in core depressive symptoms, and vice versa. Changes in sleep in response to changes in mood were only detectable the next week and not the next day, maybe because sleep responds slower to change than mood. Different groups could be identified as regards the remission of core depressive symptoms and sleep symptoms over three years, with one group showing lesser decrease of sleep compared to core symptoms. This suggests that a subgroup of patients needs more specifically targeted sleep treatment to enhance the chance of complete remission