Nurses’ Night Shifts Linked with Colon Cancer

Sunshine may be good for you and nurses who work regular night shifts have a higher risk of colon cancer, U.S. researchers reported on Tuesday.

The study by researchers at Harvard Medical School and Brigham and Women’s Hospital in Boston supports earlier research that found women who work night shifts have a higher risk of breast cancer. ‘Because night-shift work has become very common in developed countries, future studies should assess the relationship of light exposure to the risk of other cancers and consider the risks in men,’ they wrote in their report, published in the Journal of the National Cancer Institute. The U.S. Bureau of Labor Statistics estimates that about four percent of adults work rotating night shifts. Shift work disrupts normal melatonin production and increases levels of other hormones such as estrogen. Women’s cancers are often linked with estrogen, but Dr. Eva Schernhammer, who led the study, said melatonin may play a more important role. ‘While this finding needs to be replicated in future studies, the data is beginning to show that it may be melatonin, not estrogen, that is influencing cancer risk,’ she said in a statement. ‘If melatonin’s anti-cancer properties are the source of our observed effects, this research opens a whole new arena of potential associations between exposure to light and a variety of cancers.’ The researchers studied 78,586 women taking part in a long-running program called the Nurses’ Health Study. The nurses who worked night shifts at least three times a month for 15 years or more had a 35 percent greater risk of colon or rectal cancer. Melatonin is produced at night and regular exposure to sunlight affects the production cycle, which peaks in the middle of the night. Artificial light suppresses melatonin production. ‘Melatonin has well established anticarcinogenic properties, and a link between exposure at night and cancer risk through the melatonin pathway could offer one plausible explanation for the increased risk we observed,’ the researchers wrote. They noted, however, that they could be missing something and urged further study. (Source: Journal of the National Cancer Institute: Harvard Medical School, Brigham and Women’s Hospital, Boston: Maggie Fox: 4th June 2003, HealthScout)