Melatonin is a hormone produced and secreted by the pineal gland, a pine cone–shaped gland measuring less than a centimetre in length, located deep within the brain. The primary function of melatonin is the maintenance of a healthy circadian rhythm; in other words, your sleep/wake cycle. Light stops the release of melatonin, which poses a health concern for those who travel frequently and suffer from jet lag, or to shift-workers that lack this precious hormone to get their critical deep sleep to stay healthy. Melatonin production also decreases with age, which can also contribute to chronic adult insomnia.