Melatonin in Circadian Rhythm Sleep Disorders

Normal circadian rhythms are synchronized to a regular 24 hr environmental light/dark (L/D) cycle. Both suprachiasmatic nucleus (SCN) and melatonin are essential for this adaptation. Desynchronization of circadian rhythms as occurs in chronobiological disorders result in severe disturbances of sleep. The Circadian rhythm sleep Disorders (CRSDs) include delayed sleep phase syndrome (DSPS), Non 24 hr sleep/wake rhythm disorder, jet lag and shift-work. Depression also shows circadian rhythm disturbances. Disturbances in the phase position of plasma melatonin levels have been documented in all these disorders. Whether this melatonin disruption is a cause or a consequence of the disorders is not known. Further research of a larger number of patients with CRSDs can help to determine the association. At present there appears to be a role of endogenous melatonin in the pathophysiology of these circadian rhythm sleep disorders. Exogenous melatonin is useful in treating the disturbed sleep-wake rhythms seen in DSPS, Non 24 hr sleep/wake rhythm, Shift-work sleep disorder, jet lag and in depression. The magnitude and direction of the shift of the sleep-wake rhythm depend upon the time of melatonin onset. In most of these conditions an abnormal phase position of melatonin rhythm has been documented