Men who work nights are almost three times as likely to develop prostate cancer as those who do day shifts, new research shows. They are also at much greater risk of a number of other types of cancer, with higher rates of tumours in the bowel, bladder and lungs. The alarming findings, based on a study carried out in Canada, are the first to highlight the full effects of night shifts on men’s health.
Although previous studies have suggested a link with cancer, most have focused on the higher incidence of breast cancer in women working nights, mainly nurses. The latest investigation, by a team of researchers at the University of Quebec, suggests men are affected in the same way and that the effects are seen in a wide range of cancers. Night shifts are thought to harm the body through the suppression of melatonin, a hormone produced by the pineal gland in the brain that helps regulate when we sleep and when we wake. When it’s dark, melatonin output is increased to help induce deep sleep. Production normally peaks during the dark hours of night.
Scientists think exposure to night-time light disrupts the production of melatonin, setting in motion a chain of events inside the body that might encourage tumour development.
In the latest study, published in the American Journal of Epidemiology, researchers studied 3,137 men who had been diagnosed with a range of different types of cancer. As part of the study, they analysed how many of the men had regularly worked nights and compared the results with working patterns in another group of more than 500 cancer-free men.
The researchers found night shifts almost trebled the risk of prostate cancer and doubled a man’s chances of bowel cancer. Night workers were also 76% more likely to suffer lung cancer and 70% more at risk of a tumour in the bladder. For prostate, bowel and bladder cancer, the dangers were greatest among those who had worked nights for at least ten years.
In a report on their findings the researchers said: ‘Several studies have assessed the possible association between night work, particularly among nurses, and breast cancer. But little evidence has been accrued regarding cancer at other sites, or among males.
‘The observation here of elevated risks for several other types of cancer is novel.
‘One thing is certain - if our findings are valid, it would signal an important systemic (affecting the whole body) tumour hazard.’