Role of Melatonin in the Regulation of Human Circadian Rhythms and Sleep

Abstract

The circadian rhythm of pineal melatonin is the best marker of internal time under low ambient light levels. The endogenous melatonin rhythm exhibits a close association with the endogenous circadian component of the sleep propensity rhythm. This has led to the idea that melatonin is an internal sleep "facilitator" in humans, and therefore useful in the treatment of insomnia and the readjustment of circadian rhythms. There is evidence that administration of melatonin is able: (i) to induce sleep when the homeostatic drive to sleep is insufficient; (ii) to inhibit the drive for wakefulness emanating from the circadian pacemaker; and (iii) induce phase shifts in the circadian clock such that the circadian phase of increased sleep propensity occurs at a new, desired time. Therefore, exogenous melatonin can act as soporific agent, a chronohypnotic, and/or a chronobiotic. We describe the role of melatonin in the regulation of sleep, and the use of exogenous melatonin to treat sleep or circadian rhythm disorders.

Advancing a Biopsychosocial and Contextual Model of Sleep in Adolescence: A Review and Introduction to the Special Issue

“…In contrast, the circadian component of the twoprocess model is not driven by prior sleep-wake duration but is rather an intrinsic, ''internal clock'' system responsible for regulating the daily, 24-h rhythmic cycle. The secretion of melatonin, a hormone produced by the pineal gland in humans, is reliably linked to the circadian system (Cajochen et al 2003;Klerman et al 2002). These homeostatic sleep-wake and circadian systems ideally work in sync to optimally regulate sleep, but this balance is often disrupted by biological, psychosocial, and contextual changes encountered in adolescence.…”

What Keeps Us Awake?—the Role of Clocks and Hourglasses, Light, and Melatonin

“…Since then numerous laboratory studies under stringent conditions clearly demonstrated that administration of melatonin acutely affects sleep and wakeful ness in humans. Exogenous melatonin elicits all the physiological effects which occur in the evening during endogenous melatonin secretion (for a review, see Cajochen et al, 2003). Indeed, exogenous melatonin is most effective when endogenous levels are low during the biological day.…”

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