Cancer and sleep

Men who have trouble falling asleep and staying asleep are more likely to develop prostate cancer, according to a new study. (Rueben Munoz)

The links between sleep and cancer are now so many, you could build a chain. A new study has found that for men who suffer insomnia and unwelcome wakefulness, the risk of prostate cancer is greater than for those whose sleep is undisrupted.

That research expands on a growing body of evidence that men and women whose sleep is short, broken or of poor quality are at higher risk of developing a wide range of cancers.

Research has long linked overnight shift work -- and the circadian rhythm disruptions that are common with it -- as a risk factor for breast cancer and endometrial cancers in women. Last week, a large study published in the journal Sleep found that men or women who were overweight or regular snorers and who slept nine or more hours per day--a measure of sleep probably disrupted by apnea--were more likely to develop colorectal cancer.

In the latest study, published Tuesday in the journal Cancer Epidemiology, Biomarkers & Prevention, researchers asked 2,425 Icelandic men between the ages of 67 and 96 about their sleep patterns, and how often they experienced difficulty getting or staying asleep. Using a national registry, they tracked the men's medical history for between three and seven years, looking for evidence of a prostate cancer diagnosis or death of any cause.

Compared with men who reported no sleep problems, those who reported having trouble falling asleep were roughly 60% more likely to develop prostate cancer during the study period, the researchers found. And those who reported having trouble staying asleep were more than twice as likely as those with no sleep problems to be diagnosed with prostate cancer. The study's authors found some evidence that those with sleep difficulties were more likely to have advanced prostate disease than those who slept well.

Melatonin, the hormone produced by the pineal gland and reponsible for regulating our sleep-wake cycles, is widely thought to be at the heart of this link between sleep and cancer. In the lab, researchers have found that higher melatonin levels suppress tumor growth; levels close to those found in people with too much exposure to artificial light seem to promote more aggressive tumor growth in cancer cells.