Melatonin is a hormone secreted by a pea size gland, called the pineal gland. The hormone helps regulate our sleep patterns. Our levels of melatonin peak by the time we are 3 years old and remain at high levels until after middle age.

How it delays aging. Melatonin is a powerful antioxidant, says Russel J. Reiter, Ph.D., a cellular biologist at the University of Texas Health Science Center at San Antonio, author of Your Body's Natural Wonder Drug: Melatonin, and editor of the Journal of Pineal Research.

"Melatonin is one of the most powerful antioxidants there is," says Dr. Reiter. As such, it protects against age related diseases such as cardiovascular disease and cancer, which may be linked to free radical damage.

But there's more. Unlike many other antioxidants, melatonin is able to cross what's called the blood brain barrier, which means that it penetrates the brain more easily than some other antioxidants, says Dr. Reiter. So it's better able to fight the free radical damage in the brain.

Recent evidence suggests that melatonin may also slow the progression of Alzheimer's disease. "Much of the dementia associated with aging, including Alzheimer's disease, is due to loss of neurons as a result of free radical damage," says Dr. Reiter. "While very high doses of vitamin E, a well known antioxidant, given for long periods of time can slightly delay Alzheimer's, a recent study on a pair of identical twins found that as little as 6 milligrams of melatonin taken every day for 3 years substantially reduced the progression of Alzheimer's disease."

In some laboratory studies, melatonin has also been found to prevent the growth of cancer cells and to slow the growth of some tumors.

What youll find. Melatonin usually comes in 3 milligram capsules and tablets. While less common, you can find them in 1 milligram and 0.5 milligram (or 500 microgram) doses A well. Avoid so called natural melatonin supplements, which probably don't contain enough to be' effective, says Dr. Reiter. The synthetic variety, which is probably what you will find, is fine.

How much to take: You take less than you'd think. Although the generally recommended dose is 1 milligram, Dr. Reiter takes 0.5 milligram per day. 'And I have the melatonin levels of a young person," he says.

Also, always take melatonin before bed, says Dr. Reiter. And keep your room dark: Darkness stimulates the production of melatonin.

Be aware: Since melatonin makes you drowsy, don't drive or engage in any activity that requires you to be alert after taking it, says Dr. Reiter. Before you start using melatonin, talk with your doctor. Though rare, interactions with prescription medications can occur.