International Agency plans to call nightwork a probable Carcinogen

The International Agency for Research on Cancer plans to categorize overnight shift work as a probable carcinogen, according to the Associated Press. The AP says the agency will make the change in December, and the American Cancer Society is likely to follow suit. Until now, the ACS has considered the association between cancer and night work to be "uncertain, controversial or unproven." Several epidemiologic studies, done mostly on nurses and flight crews, have shown a link between night work and cancer of the breast and prostate, the
AP notes. Another analysis, prepared by the IARC, will be published in a December issue of Lancet Oncology.

In theory, sleep loss and circadian disruptions resulting from night work could contribute to cancer risk. Being exposed to light at night could disrupt production of melatonin, a hormone that can limit tumor growth.