Sleeping well may help to protect men from deadly prostate cancer, a study has found.
Scientists linked higher levels of the night-time hormone melatonin with a 75% reduced risk of advanced disease.
Melatonin is produced in the dark at night. It plays a key role in regulating the body's sleep-wake cycle and influences many other functions associated with the body's 24-hour clock, or circadian rhythm.
Low levels of the hormone are typically associated with disrupted sleep.
Scientists studied 928 Icelandic men who were questioned about their sleep patterns and had urine samples tested for levels of a melatonin breakdown product.
Men who reported taking medication for sleep problems, and difficulty falling and staying asleep, had significantly lower amounts of the melatonin marker.
Over a period of seven years, 111 of the men were diagnosed with prostate cancer including 24 with advanced disease.
Men whose melatonin marker levels were higher than the middle of the range were 75% less likely to develop advanced prostate cancer than those with lower values.
Advanced prostate cancer that has started to spread is often aggressive and likely to prove fatal.
The research was presented at the American Association for Cancer Research-Prostate Cancer Foundation Conference on Advances in Prostate Cancer Research in San Diego, US.