Melatonin is an important substance to maintain normal circadian rhythm, especially to maintain sleep cycle. When darkness stimulates the retina, a series of nerve transmission and biochemical reactions will occur in the brain, which will promote the synthesis of melatonin in pineal gland. On the contrary, during the day, light stimulates the retina and inhibits the secretion of melatonin.
Melatonin is also an active substance that regulates the biological clock. Exogenous melatonin will affect the normal secretion of melatonin in the body. People with circadian rhythm disorder (such as jet lag, blindness, night shift workers) can adjust their biological clocks by hormonal regulation of insomnia.