Clinical aspects of melatonin.

Melatonin is produced in the human pineal gland, particularly at night, with the circadian rhythm of blood melatonin levels closely paralleling its production within the pineal gland. Light exposure at night, or rapid transmeridian travel severely compromises the circadian production of melatonin. The disturbed melatonin rhythm contributes to jet lag and sleep inefficiency, both of which are improved by melatonin administration. Melatonin is also a highly effective direct free radical scavenger and antioxidant. In this capacity, melatonin reduces experimental cataractogenesis, traumatic injury to the spinal cord and brain, and protects against oxidative damage to neurons and glia in models of stroke, Parkinsonism, and Alzheimer's disease. Additionally, melatonin and its metabolites are highly effective in protecting against ionizing radiation. Finally, melatonin may be a treatment for hypertension. Melatonin's high efficacy, its high safety profile, and its virtual lack of toxicity make it of interest in clinical medicine.