Working Graveyard Shift May Up Cancer Risk

Researchers Add Overnight Shift Work To The List of "Probable" Carcinogens

(AP)  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 work day 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.

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 doesn't 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."

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.

Melatonin can be taken as a supplement, but experts don't recommend it long-term, since that could ruin the body's ability to produce it naturally.

Sleep deprivation may be another factor in cancer risk. 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 with the IARC analysis.

Not getting enough sleep makes your immune system vulnerable to attack, and less able to fight off potentially cancerous cells.

Confusing your body's natural rhythm can also lead to a breakdown of other essential tasks. "Timing is very important," Rea said. Certain processes like cell division and DNA repair happen at regular times.

Even worse than working an overnight shift is flipping between daytime and overnight work.

"The problem is re-setting your body's clock," said Aaron Blair, of the United States' National Cancer Institute, who chaired IARC's recent meeting on shift work. "If you worked at night and stayed on it, that would be less disruptive than constantly changing shifts."

Anyone whose light and dark schedule is often disrupted - including frequent long-haul travelers or insomniacs - could theoretically face the same increased cancer risk, Stevens said.

He 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."

Meanwhile, scientists are trying to come up with ways to reduce night workers' cancer risk. And some companies are experimenting with different lighting, seeking a type that doesn't affect melatonin production.

So far, the color that seems to have the least effect on melatonin is one that few people would enjoy working under: red.

[lizardbate]

I am a night worker starting at 4:00 PM til 1:30 AM or til finished, usually 3:00 - 3:30 AM. Boy, Red light???? Might have to result to smoking weed to work under red lights.

[denn034]

So does everything else nowadays.

[alphaa10-2009]

Needed--
1. Study of melatonin supplementation of male and female shift workers for one year. One supplemented group stays on night shift, another swings between day and night shifts, and another works only day shift. For each shift group, there is a comparably-sized group taking a placebo (without melatonin supplement). Study populations randomly-assigned from the same subject pool. Hypothesis-- melatonin supplementation affects cancer incidence in those working night shift. Results observed at study''s end, and at five-year followup.

2. Study of melatonin supplementation on human immune system. Study groups as defined, above. Melatonin supplementation as defined above, ceasing after a study term of one year. Hypothesis-- melatonin supplementation affects natural melatonin secretions sampled at intervals of 30 days, 90 days, 180 days, and one year after end of study.

3. Study funding-- a small percentage of the taxpayer cash thrown at inventories of JDAM "smart bombs" and cluster bomblets. Or, if you like, an equally small percentage of the cash used to buy oceans of jet fuel lacing the skies from the US to Iraq.

[grammawhamma]

I worked the night shift most of my life. I am going with the theory that sleep depravation lowers your immune system and thus can increase the risk of cancer and other diseases.

Here is another example of so call researchers with too much time on their hands. The just might stress out night workers and they did draw attention to themselves.

[chitown639]

Yeah right, I wonder how much these researhers get in government funding.

[barbaraf4]

I guess this is why Bush wants the guest workers to be here - they can take over the graveyard shift.

[barbaraf4]

"If we knew what we were doing, it wouldn''t be called Research." ~A. Einstein

[ssm9451]

Remember when they said BACON caused cancer. Next thing they''ll say is that owning a dog, causes cancer.
What will the ''researchers'' say next?

[eyewideopen]

As someone who''s working the overnight shift right now, I''ve got to say that there''s no way that this can possibly be GOOD for you!

[skinnyminny2]

re adt14...not sure what the article has to do with ''trailer parks'' and don''t understand your reference to them given they were not mentioned. The groups focused on were nurses and airline crews, and I doubt very many of them live in trailer parks (I will say I know what you mean regarding that demographic of our society--in general lower education and lacking in healthy habits).

[gaye5]

ssm9451 you forgot the other things that they say to terrorise us, like the bird flu, next they will say that the cat flu will mutate, or the dog flu, it will be something every year to make sure that the pharmaceutical companies keep their profits up by keeping the people in a constant state of fear, but people are starting to wake up.
Remember those mild childhood diseases, well they are now called killer diseases.. and yes the odd very unhealthy child had problems but millions of children every year got the mumps, measles and chicken pox, and they all lived happily ever after... Funny that when immunization kills many children every year that it is not called killer immunizations eh.. or called, "the damaging immunizations" as the numbers of children now with autism which comes on about the age of 2 years or after their second measles immunizations or those who are later dying of cancers..As a nurse we never saw it like this 40 years ago..
But oh of course, immunizations doesn''t cause any problems eh..that is why they are now proposing to give it to babies within the first year so that if it does do damage the poor mother wont know that it wasn''t born like that..A child''s own immune system doesn''t kick in until it is a year old..and why give a child hep B immunizations when the only people that are MAINLY at risk are ADULT homosexuals, and people who use needles, NOT 99% of children..it couldn''t possibly be because of profits could it..