Insomnia is a common and occasionally the initial symptom of depression. It is not related to the number of depressive episodes or to the duration of the depression, but is more common in older subjects. There is usually little difficulty in initiating sleep, but there are frequent awakenings during the night and early morning awakening, often after an unpleasant dream, especially in endogenous depression. Sleep is often unrefreshing and frequent naps may be taken during the day, especially in younger subjects.
There is a tendency towards an advanced sleep phase syndrome in depression (Fig. 7.3) which may contribute to early morning awakening . In contrast, depression in the seasonal affective disorder causes excessive daytime sleepiness and a delayed sleep phase syndrome. Changes in circadian rhythms such as cortisol secretion are common in depression. Melatonin secretion is reduced in depression, possibly because of reduced 5HT and noradrenaline stimulation of the pineal gland. The amplitude of the diurnal temperature rhythm is lessened and core body temperature at night is higher than in normal subjects. The reduction in REM sleep latency correlates with both of these abnormalities.
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