Melatonin is a hormone secreted by the pineal gland. As a supplement, it is useful for regulating sleep and the body’s daily rhythmic cycle, making it ideal for jet lag. Melatonin is also an important antioxidant that acts as an effective scavenger of free radicals. Various factors may cause melatonin levels to become low, such as inadequate dietary intake of its precursor tryptophan, low levels of serotonin, normal aging, insufficient exposure to natural light, and certain medications. Melatonin may support a healthy immune and stress response.