Study: Working Night Shift Linked to Colorectal Cancer

Working the night shift a few nights a month for a prolonged period may increase the risk of colorectal cancer in women, according to a report in the Journal of the National Cancer Institute.

Harvard University researchers, examining the relationship between night work and cancer among female participants in the Nurses’ Health Study, found that those who worked the night shift at least three times a month for 15 years or more were 35 percent more likely to develop colorectal cancer.

Other research, including a 2001 report from the ongoing Nurses Health Study, has suggested that working rotating night shifts raises the risk of breast cancer.

Researchers theorize that lowered levels of melatonin, which appears to inhibit tumor growth, might be the factor in increasing cancer risk. Melatonin levels usually peak in the middle of the night.

"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 reported.

Other Sources: Journal of the National Cancer Institute