Sleep, melatonin, and cardiovascular disease

Melatonin is a key circadian mediator that governs the synchronisation of peripheral biological rhythms with the central clock (ie, the suprachiasmatic nucleus) and regulates the sleep–wake cycle. The synthesis of this hormone by the pineal gland follows a nyctohemeral pattern that aligns with the day–light cycle: production is low during the day and high at night. The rhythmic secretion of melatonin from the pineal gland is controlled by a multisynaptic pathway, through the retinal–hypothalamic–suprachiasmatic nucleus tract to the superior cervical ganglia.