Effects of melatonin on the circadian functions of sleep-wake cycle, metabolism, hormonal regulation and immune activity: A recent review

Rhythms following a period of approximately 24 hours are called circadian (from Latin circa diem, approximately one day) rhythms. These rhythms are observed in the activities of various vital body functions. Melatonin is considered as an important molecule participating in the formation of circadian rhythms of virtually all organisms. As a molecular regulator of the circadian clock, melatonin has various regulatory functions in both physiological and pathological conditions. Sleep-wake cycle depends on CSF melatonin levels, and melatonin also has a protective effect on the disrupted sleep-wake cycle in various pathological conditions. Melatonin ensures the proper function of vital metabolic pathways; therefore, it improves metabolism-related systems and protects them from damage. A bidirectional relationship between hormonal activity and melatonin ensures it having a healing effect on various reproductive disorders. Finally, melatonin can target inflammation pathways and various elements of immune system by changing their behavior and structure. In summary, melatonin has important effects on vital body functions mediated by its receptors, signaling pathways and clock genes, and has the capacity to protect and improve these functions under pathological conditions.