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Working at night: Cancer hazard?

Once "uncertain," overnight shift work will be listed as a probable carcinogen.

By Associated press
Published November 30, 2007


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LONDON - Like UV rays and diesel exhaust fumes, working the graveyard shift will soon be listed as a "probable" cause of cancer.

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 American Cancer Society says it will likely follow. Up to now, the U.S. organization has considered the work-cancer link to be "uncertain, controversial or unproven."

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.

The analysis will be published in the December issue of the journal Lancet Oncology.

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.

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.

To put the risk in perspective, the "probable carcinogen" tag means that the link between overnight work and cancer is merely plausible.

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.

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.

[Last modified November 30, 2007, 01:32:56]


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