What it is

Melatonin is made from tryptophan through serotonin, mainly in the pineal gland at night, and also in the gut, the retina and the mitochondria of many cells. Light on the eyes switches its production off within minutes. Its night-time peak tells the body how long the night is, which sets sleep, hormones and the seasons. It is cleared by the liver in under an hour, so timing matters more than amount.