Melatonin is a natural hormone made by the pineal gland from tryptophan and is critically involved in daily circadian body rhythms. Seasonal cycles in many species are controlled by the annually recurring changes in day length which in turn are perceived via melatonin secretion. The activity of the enzyme serotonin-n-acetyl-transferase is increased 30 – 60 fold during the dark with normal production of melatonin being almost exclusively at night. It has also been suggested that melatonin is a potent antioxidant, immune stimulant and inhibitor of cancer. Animal studies have shown in increased incidence of carcinogen-induced tumors in mice that had their pineal glands removed which was reversed by the addition of melatonin. In humans, melatonin functions in regulating normal sleep/wake cycles and has been used as a natural sleep aid and in treating symptoms related to jet lag. Melatonin decreased with age and its role in the aging process is being investigated.

Supplementation with melatonin as a sleep aid is becoming more common but optimal effective doses have not been defined. Melatonin is highly lipophilic and salivary levels are a direct reflection of serum concentrations.