Night Shift Linked to Cancer / Night Work Tied to Lower Levels of a Hormone That Can Prevent Tumors From Developing
Like UV rays and diesel exhaust fumes, working the graveyard shift will soon be listed as a “probable” cause of cancer.
It is a surprising step validating a concept once considered wacky. And it is based on research that finds higher rates of breast and prostate cancer among women and men whose workday starts after dark.
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.
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.
However, 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.
If the graveyard-shift theory eventually proves correct, millions of people worldwide could be affected. Experts estimate that nearly 20 percent of the working population in developed countries work night shifts.
Some Richmond police officers are assigned to a permanent midnight shift, Richmond police Lt. Emmett Williams said.
“If the study pans out, they [the officers] would start to show a deal of concern about their health,” Williams said. “If it had legs and down the road, it would have to be something to have a serious look at.”
Among the first to spot the night shift-cancer connection was 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 over many years were indeed more prone to breast cancer. Also, animals that have their light-dark schedules switched develop more cancerous tumors and die earlier.
Some research also suggests that men working at night may have a higher rate of prostate cancer.
Because these studies mostly focused on nurses and airline crews, bigger studies in different populations are needed to confirm or disprove the findings.
There are still plenty of skeptics. And to put the risk in perspective, the “probable carcinogen” tag means that the link between overnight work and cancer is merely plausible.
Among the long list of agents that are listed as “known” carcinogens are alcoholic beverages and birth-control pills. Such lists say nothing about exposure amount or length of time or how likely they are to cause cancer.
The American Cancer Society Web site notes that carcinogens do not always cause cancer. The cancer society does not make its own assessments of possible cancer-causing agents but relies on analyses by the IARC and a U.S. agency.
Still, many doubters of the night-shift link may be won over by the IARC’s analysis to be published in the December issue of the journal Lancet Oncology.
“The indications are positive,” said Vincent Cogliano, who heads up the agency’s carcinogen classifications unit. “There was enough of a pattern in people who do shift work to recognize that there’s an increase in cancer, but we can’t rule out the possibility of other factors.”
A clerk at an all-night drugstore in Richmond called the idea of linking graveyard-shift work to cancer “wacky.” But she said working the shift affected her when she went to day hours.
“I had a really hard time adapting to the new schedule,” she said. “It does really make a difference.”
Traci Brown, manager of the 3rd St. Diner at 218 E. Main St., said, “It’s a theory. You’re all right as long as you get your sleep.”
Cancer risk
Anyone whose light and dark schedule is often disrupted – including frequent long-haul travelers or insomniacs – could theoretically face an increased cancer risk, says cancer epidemiologist Richard Stevens.
What to do
Stevens advises workers to sleep in a darkened room once they get off work. “The balance between light and dark is very important for your body. Just get a dark night’s sleep.”
Staff writer Bill Wasson contributed to this report.
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Originally published by Staff and Wire Reports.
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