Jan 20, 2014 03:02 PM EST By Russell Westerholm, UniversityHerald Reporter

A new study has made a link between melatonin and a lower risk of prostate cancer, but it is not yet enough to confirm the sleep hormone prevents the disease.

According to HealthDay News, the study tracked 928 Icelandic men and those with higher melatonin levels had a lower prostate cancer risk. The study was presented Sunday at an American Association for Cancer Research meeting focused on prostate cancer in San Diego.

"Men who had higher levels of melatonin had a 75 percent reduced risk for developing advanced prostate cancer compared with men who had lower melatonin," Sarah Markt, a doctoral candidate in the department of epidemiology at Harvard School of Public Health, told HealthDay. "The risk was especially reduced when it came to advanced disease."

Even if the study's results are confirmed, men may not have it so easy to ensure they get a good night's sleep every night to prevent prostate cancer. Markt said melatonin is necessarily produced by sleep. Widely believed to be connected to the body's circadian rhythms, melatonin is secreted by the pineal gland at night, signifying the biochemical notion of darkness.

"In experimental studies - animal studies and prostate cancer cell lines - it's been shown that melatonin has an inhibiting effect on prostate tumor growth," Markt said.

For the study, the researchers gathered data on men from Iceland between 2002 and 2009. The men gave urine samples for melatonin levels, then were linked to cancer and death records. To accompany the data, the researchers also had the participants fill out a questionnaire about sleep patterns.

Not associated with the study, Dr. Stephen Freedland, an associate professor of urology and pathology at Duke University, said there may not be a cause-and-effect relationship between the two, but the results may not take other factors into account.

"One confounding factor is that these are men in Iceland," Freedland told HealthDay. "They spend practically six months of the year with no sunlight and six months with sunlight. What time of year was this done? There's actually data that suggest sunlight may be good for prostate cancer."

Markt also said the findings do not prove melatonin lowers prostate cancer risk, adding: "Prospective studies to investigate the interplay between sleep duration, sleep disturbance and melatonin levels on the risk for prostate cancer are needed."

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