Melatonin Linked to Prostate Cancer Risk

Men with higher levels of the sleep hormone melatonin may be less likely to develop prostate cancer, a new study suggests.

The research also revealed that men who had higher levels of melatonin in their urine had a 75 percent decreased risk of advanced prostate cancer, compared with men with lower melatonin levels.

"It's notable that we found a stronger association between melatonin levels and more advanced prostate cancer," said study researcher Sarah Markt, a doctoral candidate in the department of epidemiology at the Harvard School of Public Health in Boston.

People's melatonin levels are affected by the amount of sleep they get, and the quality of that sleep. The hormone is produced in the brain by the pineal gland in response to darkness.

Melatonin levels typically rise in the evening, promoting sleep, and peak during the night. Levels then fall in the morning, as sunlight and indoor light use increases, encouraging wakefulness.

But people who have irregular sleep schedules from shift work hours, as well as people who wake up a lot during the night and turn on the lights, disrupt their circadian rhythm — the body's internal clock — and produce less melatonin, the researchers said.

The research was presented today (Jan. 19) at the American Association for Cancer Research Conference on Advances in Prostate Cancer Research in San Diego. It has not yet been published in a peer-reviewed journal. [Top 10 Cancer-Fighting Foods]

Melatonin and cancer

Earlier research has suggested that melatonin plays a role in regulating hormones that influence cancer. Test-tube studies have shown that melatonin may help slow or stop the growth of cancer cells. 

And there's some evidence that women who work night shifts for many years have lower levels of melatonin and a slightly higher risk of breast cancer, according to the American Cancer Society.

To find out how disrupted sleep may influence melatonin production and prostate-cancer risk,the researchers looked at data from nearly 930 men in Iceland between 2002 and 2009.

The researchers asked the men to complete a questionnaire, describing their usual sleep habits, and to provide a urine sample from their first morning bathroom visit, which is considered a good marker of melatonin production.

Among the participants, 111 men were eventually diagnosed with prostate cancer, 24 of whom had an advanced stage of the disease. 

The study found that men who had melatonin levels above the midpoint of 17.1 nanograms per milliliter had a 30 percent lower overall risk of prostate cancer, and a 75 percent lower risk of developing an advanced form of the disease, compared with men whose melatonin levels were below the midpoint.

Sleep and prostate cancer

The findings also showed that one in seven men reported problems falling asleep, one in five men had trouble staying asleep and nearly one in three men took sleeping pills.

Men with sleep problems — those who took sleep medications, or had trouble falling asleep or staying asleep— had lower levels of melatonin than men with no difficulty sleeping.

Because the sleep questionnaire did not ask men whether they used the dietary supplement melatonin as a sleep aid, there was no way to tell if the men's melatonin levels resulted from the naturally occurring form of the hormone or melatonin supplements, Markt said.

This is the first study to show a link between melatonin levels and prostate-cancer risk using urine samples collected before the men were diagnosed with the disease, Markt said. 

Although the study was small and the results need to be replicated, these findings are important because they provide further support for the idea that men's circadian rhythms influence prostate-cancer development, Markt said.

Two of the best ways to preserve melatonin production are to keep a regular sleep schedule and to avoid light at night from sources like a television, computer screen, lamp or other type of indoor lighting, Markt said. 

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