It sounds like a nutty idea. Graveyard shift having anything to do with cancer risk? But at one time, that was how people felt about smoking and cancer, and we know what happened there.
Next month, the International Agency for Research on Cancer (IARC), the World Health Organization's cancer arm, will classify shift work as a "probable" carcinogen. At the same time, the American Cancer Society has indicated that once that classification takes place, it would most likely add shift work to its list of "known and probable carcinogens." Until now, the ACS has labeled shift work an "uncertain, controversial or unproven effect."
How did this reclassification take place?
The idea is isn't new; it was first posited in 1987 by Richard Stevens, a cancer epidemiologist and professor at the University of Connecticut Health Center. He published a paper suggesting a link between light at night and breast cancer. Naturally he was ridiculed.
However, recent studies have shown a correlation between women working at night for many years and an increased risk of breast cancer, and also that men working at night may have a higher rate of prostate cancer.
There have also been studies associating a higher incidence of tumors in animals who have had their light-dark schedules switched.
And that's the theory. One: that shift work disrupts the circadian rhythm, the body 24-hour physiological cycle --- and two: that the hormone melatonin, which suppresses tumor development and is normally produced at night, is suppressed in shift workers because light shuts down its production.
Additional possible contributors: lack of sleep and flipping between shift work and regular hours. No matter what, however, researchers say more studies are required.
One other thing: researchers recommend that shift workers make sure they sleep in a darkened room when they return home. This also ought to be a warning to those of you who fall alseep while watching TV, as sleeping with a lot of light is what researchers are concerned about.