Melatonin is secreted by the pineal gland. It is a circadian rhythm hormone-thereby affecting the patterns of sleep. Research has shown that the cells of the body rejuvenate and repair during the deeper stages of sleep. It is during the deeper stages of sleep that the body produces natural killer cells or CD4 cells. Melatonin increases the deep stage of sleep and stage IV sleep, thereby increasing and enhancing immunity. Improved sleep patterns serve to energize the body and improve mood. Melatonin has tremendous cancer prevention effects due to its enhancement of the immune system. Melatonin deficiency results in poor sleep, jet lag, irritability, hypersensitivity and premature aging.