Circadian rhythm sleep disorders

In modern societies, there has been an increasing awareness of persistent circadian rhythm sleep disorders. In our 24-h society, under conditions which may disrupt normal day-night activities such as shift work, jet lag, affective disorders, or intense bright light late at night, a desynchronization of circadian rhythms can occur resulting in circadian rhythm sleep disorders. Circadian rhythms are major features of adaptation to our environment. In mammals, circadian rhythms are generated and regulated by a circadian timing system. Disorders of circadian timing primarily affect entrainment function to the normal day-night cycle. The major feature of these disorders is a misalignment between the patient\u27s sleep pattern and the sleep pattern that is desired or regarded as the societal norm. These disorders are classified as circadian rhythm sleep disorders in ICSD-2 (the International Classification of Sleep Disorders: second edition; 2005), consisting of: 1) Delayed sleep phase type characterized by a persistent inability to fall asleep and arise at conventional clock times; the phase of the sleep-wake cycle is delayed. 2) Advanced sleep phase type: affected individuals complain of sleepiness in the late afternoon or early sleep onset, and early morning awaking. 3) Irregular sleep-wake type consisting of temporally disorganized sleep period: there is no major sleep period, instead patients presents variable episodes in sleeping and waking behaviors. 4) Free-running type which consists of a chronic steady pattern comprising one- to two-hour daily delays in sleep onset and wake times in an individual living in society. 5) Jet lag type. 6) Shift work type: the shift workers complain of difficulty initiating and maintaining sleep and poor sleep quality. For these patients with circadian rhythm sleep disorders, chronobiological treatments such as resetting daily-life schedule, enforcement of zeitgebers, bright light therapy, melatonin, or vitamin B_ treatment are effective