Melatonin is a hormone secreted by the pineal gland in the brain. Better known as the ‘sleep hormone’ or ‘hormone of darkness’, it plays a central role in regulating the body’s biological clock by promoting drowsiness. Melatonin has the particular feature of being triggered by darkness and inhibited by light. Available in dietary supplement form, melatonin is good for relieving jetlag. Scientists are also interested in its potential for preventing sleep problems, its antioxidant power against oxidative stress and its effects on the immune system.