Insomnia can double the risk of prostate cancer, a study has claimed.
The risk rises proportionately with the severity of sleep problems, researchers found, increasing from 1.6 to 2.1 times the usual level.
Why poor sleep can affect men's chances of developing the disease is unexplained.
“Sleep problems are very common in modern society and can have adverse health consequences,” said study leader Dr Lara Sigurdardottir, from the University of Iceland in Reykjavik.
“Women with sleep disruption have consistently been reported to be at an increased risk for breast cancer, but less is known about the potential role of sleep problems in prostate cancer.”
The researchers studied more than 2,000 men aged 67 to 96 and quizzed them about their sleeping habits.
Compared with men who had no problems sleeping, those suffering from insomnia were significantly more likely to develop prostate cancer.
The findings are published in the journal Cancer Epidemiology, Biomarkers & Prevention.