The conclusion is based on research that finds higher rates of bre.ast and prostate cancer among women and men whose work day starts after dark.
Scientists suspect that overnight work is dangerous because it disrupts the circadian rhythm, the body’s biological clock. The hormone melatonin, which can suppress tumor development, is normally produced at night. According to Reuters, next month, the International Agency for Research on Cancer, the cancer arm of the World Health Organization, will add overnight shift work as a probable carcinogen, and the American Cancer Society says it will likely follow. Up to now, the U.S. organization has considered the work-cancer link to be “uncertain, controversial, or unproven.”
Also, it appears that even worse than working an overnight shift is flipping between daytime and overnight work.
Of course, the higher cancer rates don’t prove working overnight can cause cancer. There may be other factors common among graveyard shift workers that raise their risk for cancer, according to the report. Still, scientists suspect that overnight work is dangerous because it disrupts the circadian rhythm, the body’s biological clock. The hormone melatonin – which can suppress tumor development – is normally produced at night. Scientists believe having lower melatonin levels can raise the risk of developing cancer. Light shuts down melatonin production, so people working in artificial light at night may have lower melatonin levels.
Some companies are experimenting with different lighting, seeking a type that doesn't affect melatonin production. Thus far the color that seems to have the least effect on melatonin - red.
Despite the scintillating headlines, the "probable carcinogen" tag simply means that the link between overnight work and cancer is merely plausible. Also bear in mind that the list of "known" carcinogens includes things such as alcoholic beverages and birth control pills.
The IARC's analysis will be published in the December issue of the journal Lancet Oncology.
See also "working the nightshift" at http://www.publicbroadcasting.net/wnpr/news.newsmain?action=article&ARTICLE_ID=1191168
The Lancet at http://www.thelancet.com/journals/lancet