Melatonin may help sleep-and-wake rhythms

Melatonin is secreted by the pineal gland, a tiny hormone-producing organ in the brain. Researchers say that, in animals, the hormone helps determine hibernation patterns. In humans, it is responsible for the circadian rhythm -- the biological cycle that dictates when we sleep and wake. It also plays a role in sexual development.

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Uses: The hormone is used primarily to fight insomnia and jet lag and, particularly among older adults, improve sleep quality. It’s also sometimes used in efforts to prevent Alzheimer’s disease and cancer.

Dose: Only a very small dose of melatonin -- 0.3 to 1 milligram -- is needed to help regulate sleep. Note that many over-the-counter melatonin supplements contain much higher doses of the hormone per pill. To improve sleep, take the hormone an hour or two before bed (when the brain normally boosts production).

Precautions: Taking excessively large doses of the hormone can drastically reduce its effectiveness, so take the smallest amount necessary. Women attempting to get pregnant should avoid the hormone since it may lower the likelihood of conception.

It may also aggravate symptoms of depression. Little is known about the safety of long-term melatonin use, and some researchers caution that taking too much of the hormone could produce unwanted side effects. A recent study, for example, showed that in certain birds, supplemental melatonin causes reproductive organs to shrink.

Research: Human studies on melatonin have produced a mixed bag of evidence, but a review earlier this year of 17 well-designed studies concluded that the hormone is, in fact, effective in regulating and improving sleep. In animal, lab and some human studies, melatonin shows promise for preventing and treating cancer, particularly colon cancer, but it also may worsen the disease in animals with certain cancers, such as leukemia. Preliminary studies suggest melatonin may help conquer nicotine addiction, high blood pressure and chronic headaches, among other conditions.

Dietary supplement makers are not required by the U.S. government to demonstrate that their products are safe or effective. Ask your healthcare provider for advice on selecting a brand.

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-- Elena Conis