The therapeutic potential of melatonin: a review of the science.

Melatonin is a ubiquitous natural neurotransmitter-like compound produced primarily by the pineal gland. This agent is involved in numerous aspects of the biological and physiologic regulation of body functions. The role of endogenous melatonin in circadian rhythm disturbances and sleep disorders is well established. Some studies have shown that melatonin may also be effective in breast cancer, fibrocystic breast diseases, and colon cancer. Melatonin has been shown to modify immunity, the stress response, and certain aspects of the aging process; some studies have demonstrated improvements in sleep disturbances and “sundowning” in patients with Alzheimer's disease. The antioxidant role of melatonin may be of potential use for conditions in which oxidative stress is involved in the pathophysiologic processes. The multiplicity of actions and variety of biological effects of melatonin suggest the potential for a range of clinical and wellness-enhancing uses. This review summarizes the physiology of melatonin and discusses the potential therapeutic uses of melatonin. Melatonin is a widely occurring neurotransmitter-like compound derived primarily from the pineal gland. It is also produced in a number of other areas, for example the gastrointestinal tract.[1–3] Once labeled as a master hormone, it has been found to be involved in numerous aspects of biological and physiologic regulation. Synthesis and Physiologic Role in Humans Melatonin is an indole hormone, widely distributed in both plant and animal sources, such as human milk,[4] bananas, beets, cucumbers, and tomatoes.[5] Chemically, melatonin is N-acetyl-5-methoxytryptamine, a derivative of serotonin, which in turn is derived from tryptophan. Serotonin is first acetylated by N-acetyltransferase (probably the rate-limiting step) and then methylated by hydroxyindole orthomethyltransferase to form melatonin.[6] Melatonin synthesis depends on intact beta-adrenergic receptor function.[7] Norepinephrine activates the N-acetyltransferase and beta-receptor blockers depress melatonin secretion.[8] The enzymes of melatonin synthesis are activated and depressed, respectively, by darkness and light. Release of melatonin follows a circadian (circa: about; dias: a day) rhythm generated by the suprachiasmatic nuclei in response to daylight alterations. Through melatonin release, the pineal gland maintains the internal clock governing the natural rhythms of body function. This apparent clock-setting property of melatonin has led to the suggestion that it is a “chronobiotic” substance that alters and potentially normalizes biological rhythms and adjusts the timing of other critical processes and biomolecules (hormones, neurotransmitters, etc) that, in turn, exert numerous peripheral actions.[9]