Est-ce que l'OMS va aussi recommender les patients de ne pas tomber malade
durant la nuit, puisque c'est probablement cancerigene pour les autres?
txt
Working night shift 'probable' cancer cause
November 29, 2007
FROM THE ASSOCIATED PRESS
LONDON — 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.
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