Melatonin is the all-natural nightcap. It's secreted by the pineal gland, a pea-size structure at the center of the brain, as our eyes register the fall of darkness. At night, melatonin is produced to help our bodies regulate our sleep-wake cycles. The amount of melatonin produced by our body seems to lessen as we get older. Scientists believe this may be why young people have less problem sleeping than older people.