Melatonin Zn Se is a supplement that has ingredients that mimic the action of melatonin allowing a person to feel alert and refreshed. In the body, the circadian rhythm, also referred to as the sleep wake cycle, is regulated by a substance known as melatonin that is produced by the pineal gland at night. However, as age catches up, the amount of melatonin released by the pineal gland reduces thereby resulting in older people having less sleep or low quality of sleep.