Q. I've heard that melatonin can help people sleep, and that it also has major health benefits, especially in regard to cancer. Can you explain?

A. Melatonin, a hormone released naturally in your brain, may not only help you sleep but may also help prevent diseases, including cancer. Research shows that sleep is essential for optimal health, but sleep that allows you to release adequate levels of melatonin is even more important.

Melatonin is produced from the amino acid L-tryptophan within your pineal gland, which is under the control of your retina, the light-sensitive part of your eye. During darkness, your pineal gland produces peak levels of melatonin — not only helping you fall asleep, but also acting as a powerful antioxidant in your body. If light shines on your eyes during the night, however, your pineal gland produces less melatonin and your sleep patterns can be disrupted, potentially altering your circadian rhythms (the daily temporal cycles of your biological processes). Research shows an association between low melatonin production, heart disease, breast cancer and prostate cancer. To get a good night's rest, make your bedroom as dark as you can — remove all electric lights, including even your alarm clock — and wear an eye mask if possible.

Another way to protect your healthy melatonin production is to avoid shift work. A 2010 article in Occupational Medicine points out that "shift work is associated with an increased risk of major disease (heart disease and cancer) and this may also, at least in part, be attributed to frequent circadian desynchrony" (a state in which circadian rhythms are thrown off.)

According to a 2009 article in the journal Integrative Cancer Therapies, melatonin "suppresses the development and growth of breast cancer by regulation of growth factors, regulation of gene expression ... inhibition of tumor cell invasion and metastasis." In a recent article in the Scandinavian Journal of Work, Environment, and Health, research on shift work suggests that melatonin suppression through exposure to light at night could contribute to breast cancer in women and prostate cancer in men.

For women who have been diagnosed with breast cancer that is responsive to estrogen, melatonin may play a role in preventing a recurrence, according to a Journal of Biological Chemistry article in 2004.

In addition to increasing your body's production of melatonin with lifestyle changes, you can take melatonin as a dietary supplement, available over the counter at drugstores and health food stores. The recommended dose is a 0.5 to 3 milligram tablet taken sublingually (under your tongue) right before sleep.