Men with higher levels of melatonin, a hormone involved in the sleep-wake cycle, had a 75 per cent reduced risk for developing advanced prostate cancer compared with men who had lower levels of melatonin, researchers found.
Melatonin is produced exclusively at night in the dark and is an important output of the circadian rhythm.
"Sleep loss and other factors can influence the amount of melatonin secretion or block it altogether, and health problems associated with low melatonin, disrupted sleep, and/or disruption of the circadian rhythm are broad, including a potential risk factor for cancer," said Sarah C Markt, doctoral candidate in the Department of Epidemiology at Harvard School of Public Health in Boston.
"We found that men who had higher levels of melatonin had a 75 per cent reduced risk for developing advanced prostate cancer compared with men who had lower levels of melatonin," Markt said.
"Our results require replication, but support the public health implication of the importance of maintaining a stable light-dark and sleep-wake cycle.
"Because melatonin levels are potentially modifiable, further studies of melatonin and prostate cancer risk and progression are warranted," added Markt.
To investigate the association between urine levels of the main breakdown product of melatonin, 6-sulfatoxymelatonin, and risk of prostate cancer, Markt and colleagues conducted a case-cohort study of 928 Icelandic men from the AGES-Reykjavik cohort between 2002 and 2009.
They collected first morning void urine samples at recruitment, and asked the participants to answer a questionnaire about sleep patterns.
The researchers found that one in seven men reported problems falling asleep, one in five men reported problems staying asleep, and almost one in three reported taking sleeping medications.
The median value of 6-sulfatoxymelatonin in the study participants was 17.14 nanogrammes per millilitre of urine.
Men who reported taking medications for sleep, problems falling asleep, and problems staying asleep had significantly lower 6-sulfatoxymelatonin levels compared with men without sleep problems, according to Markt.
Of the study participants, 111 men were diagnosed with prostate cancer, including 24 with advanced disease.
The researchers found that men whose 6-sulfatoxymelatonin levels were higher than the median value had a 75 per cent decreased risk for advanced prostate cancer.
A 31 per cent decreased risk for prostate cancer overall was observed as well, but this finding was not statistically significant.
The study was presented at a meeting of the American Association for Cancer Research.