Melatonin and sleep: Exploring its role in regulating the circadian rhythm and sleep-wake cycle.

Abstract

Sleep is a vital physiological process essential for maintaining overall health, supporting cellular repair, immune regulation, and cognitive functions. Sleep disruptions are associated with adverse health outcomes, including cardiovascular diseases, metabolic disorders, and impaired mental health. Sleep regulation is orchestrated by the circadian rhythm and homeostatic sleep drive, with melatonin-a neurohormone secreted by the pineal gland-playing a pivotal role in modulating these processes. Melatonin synthesis follows a biochemical pathway, converting serotonin to melatonin through key enzymes, AANAT and HIOMT, under circadian control. The suprachiasmatic nucleus (SCN) governs its secretion via light-responsive pathways, with light exposure inhibiting and darkness stimulating melatonin production. Acting through MT1 and MT2 receptors in the SCN and other brain regions, melatonin facilitates sleep onset, circadian rhythm alignment, and sleep maintenance while exerting antioxidant, anti-inflammatory, and chronobiotic effects. Exogenous melatonin has emerged as a therapeutic agent for managing sleep disorders, such as circadian rhythm sleep-wake disorders, jet lag, and insomnia. Its chronobiotic properties enable circadian phase-shifting, aligning sleep-wake cycles with environmental cues. Despite its growing use, questions remain regarding optimal dosing and long-term safety. This review delves into the physiology of melatonin, its synthesis, regulation, and mechanisms of action in sleep regulation. It also examines its therapeutic potential, highlighting gaps in research and paving the way for future studies on melatonin's broader implications in health and disease.