(The Best Years in Life) Melatonin is nature's sleeping pill. It is secreted by the light sensitive pineal gland which regulates our biological clock and synchronizes our hormonal-immune network in what is known as the circadian rhythm. Our level of melatonin naturally rises with darkness and falls with light. According to Dr. Uzzi Reiss, in his book Natural Hormone Balance, a healthy pineal gland produces 2.5 milligrams of melatonin every twenty-four hours. Melatonin plays a central role in the aging processes of the body. When pineal production of melatonin begins to diminish at around age 40, the decline sets off changes in the operation of the body's cells. The physiology of the cell shifts from repair and rejuvenation to aging and degeneration. Read More.