Cigarettes, Toxic Waste, Graveyard Shift

What do the above three things have in common? According to the International Agency for Research on Cancer, they are all probable carcinogens: It is a surprising twist for an idea that scientists first described as "wacky," said Richard Stevens, a cancer epidemiologist and professor at the University of Connecticut Health Center. In 1987, Stevens published a paper suggesting a link between light at night and breast cancer. Back then, he was trying to figure out why breast cancer incidence suddenly shot up starting in the 1930s in industrialized societies, where nighttime work was considered a hallmark of progress. Most scientists were bewildered by his proposal. But in recent years, several studies have found that women working at night for many years are indeed more prone to breast cancer, and that animals who have their light-dark schedules switched grow more cancerous tumors and die quicker. … Scientists suspect that shift 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. Light shuts down melatonin production, so people working in artificial light at night may have lower melatonin levels, which scientists think can raise their chances of developing cancer. Sleep deprivation may also be a factor. People who work at night are not usually able to completely reverse their day and night cycles. "Night shift people tend to be day shift people who are trying to stay awake at night," said Mark Rea, director of the Light Research Center at Rensselaer Polytechnic Institute in New York, who is not connected to IARC or its expert panel. Not getting enough sleep makes your immune system vulnerable to attack, and less able to fight off potentially cancerous cells. While there are still "outside factors" to consider (including testing a broader population base), this re-classification could mark a significant change in the way we look at disease--and maybe even raise awareness regarding social status as a predicate for devastating illness.