Melatonin is produced in the dark, while we sleep, and wanes upon daybreak: bright light signals the production cycle to shut down. It is secreted by the pineal gland, a small organ set behind and between the eyes. The pineal is called the "third eye," a reference to our evolutionary heritage-a time when the pineal may have extended the sensory capacities. The pineal gland serves as the timekeeper of the brain, helping to govern the sleep-wake cycle and, in animals, seasonal rhythms of migration, mating, and hibernation. In the human population, melatonin levels are highest in children.

Melatonin is made from an amino acid called tryptophan. Tryptophan is an essential amino acid-we can get it only from the foods that we ingest. The tryptophan we consume during the day is converted into serotonin, a brain chemical involved with mood. Serotonin, in turn, is converted into melatonin.

WHAT MELATONIN DOES

Although research on melatonin has been ongoing since its discovery in 1958, it is only recently it has attracted high interest. Why? Research breakthroughs over the past decade have revealed some startling properties of this amazing substance:

• Studies by immunologist Dr. Walter Pierpaoli of the Biancalana-Masera Foundation for the Aged in Ancona, Italy, and various colleagues have shown that melatonin treatments extended the life span of mice by as much as 25 percent. Moreover, mice that had been treated with melatonin not only lived longer, they also appeared younger, healthier, more vigorous, and sexually rejuvenated.
  
• Researchers at Tulane University School of Medicine in New Orleans have done studies suggesting that melatonin can stop or retard the growth of human breast cancer cells. Cancer specialists in Milan have added melatonin treatments to chemotherapy and immunotherapy in their treatment of cancer patients. They have found that such patients experienced tumor regression, in addition to living longer and suffering from fewer side effects than patients who received chemotherapy and immunotherapy alone.
  
• Studies suggest that melatonin may be a kind of "natural" sleeping pill, inducing sleep without suppressing REM (dream) sleep and without producing side effects, such as those caused by sedatives and other artificial sleep aids.
  
• Travelers have found that by using melatonin they can "reset their biological clocks" after flying across one or more time zones. Numerous studies have confirmed melatonin's efficacy in combating jet lag and restoring restful sleep patterns.
  
• Melatonin may help to prevent heart disease by lowering blood cholesterol in people with high cholesterol. (Interestingly, melatonin seems to have no such effect on those with normal cholesterol.)
  
• In a study conducted by the Medical University of Lodz (Poland) in April 2002, women between ages sixty-four and eighty years took melatonin at bedtime for six months, and were found to have a slight but significant increase in IGF-1 and an increased level of DHEA.
  
• New research suggests that melatonin may be effective in combating, treating, or preventing AIDS, Alzheimer's disease, Parkinson's disease, asthma, cataracts, diabetes, and Down's syndrome. Some scientists also believe that it may be the basis of a new estrogen-free birth control pill that combats breast cancer at the same time that it prevents conception.

Studies conducted by pioneering University of Texas melatonin researcher Dr. Russel Reiter show melatonin to be the most potent scavenger of free radicals-unstable molecules that promote cancer and heart disease by damaging DNA, cells, and tissue.