Taking supplements of the hormone melatonin has been purported to relieve insomnia, but the evidence for its effectiveness is mixed. Should you try it?

Anyone who's had insomnia knows how frustrating it can be. There are a variety of prescription and over-the-counter sleep aids available, one of which is the hormone melatonin, sold in the form of a dietary supplement.

Although we often don't notice them, many of our bodily functions, including the rise and fall of blood pressure and changes in body temperature, run on a daily cycle called a circadian rhythm. Sleep also follows a circadian rhythm.

Melatonin is a naturally occurring hormone that plays an integral role in regulating sleep patterns. It is produced by a tiny, light-sensitive gland at the center of the brain known as the pineal gland.

During the day, light causes the retina of the eye to send continuous impulses to the pineal gland, shutting down the production of melatonin. As darkness falls and light impulses sent to the brain begin to decrease, the pineal gland begins to secrete melatonin, which induces sleep. These secretions continue throughout the night, until morning light begins to stimulate the retina to start sending impulses to the brain again, decreasing the secretion of melatonin until you wake up.

When this rhythmic cycle of melatonin secretion is thrown off, such as when traveling across multiple time zones, sleeping problems may result. The problem can be caused by defects in either direction. If melatonin production continues into the morning, or, in some cases, all day, drowsiness may result. Usually, however, the problem occurs in the other direction. If insufficient amounts of melatonin are secreted early enough in the evening, it is difficult to fall asleep. And if not enough melatonin is secreted during the night or the secretion ends too soon, you may get an inadequate amount of sleep.