Shift work may cause cancer, world agency says

Shift work may cause cancer, world agency says
WASHINGTON (Reuters) - Shift workers and firefighters havea higher risk of cancer than the general population and suchwork should be classified as probably or possibly carcinogenic,the International Agency for Research on Cancer said on Friday.
A team of 24 scientists who sifted through the evidencesaid more studies must confirm the link, but found that shiftwork that disturbs the body's internal clock appears to havecancer-causing effects, too.
This internal clock regulates circadian rhythms, a complexsystem that signals cells to produce various hormones atvarious times.
"Shiftwork that involves circadian disruption is probablycarcinogenic to humans," the French-based IARC, the canceragency of the World Health Organization, said in a statement."Occupational exposure as a firefighter is possiblycarcinogenic to humans," it added.
The statement, published as what the IARC calls amonograph, could affect a significant number of people.
"Nearly 20 percent of the working population in Europe andNorth America is engaged in shiftwork. Shiftwork is mostprevalent in the health-care, industrial, transportation,communications, and hospitality sectors," the IARC said.
But the IARC's Vincent Cogliano said the evidence was notyet clear enough for anyone to take any action.
"I don't know if this is ready for an employer yet becauseI don't think we understand fully what it is about shift workthat might be causing cancer," Cogliano said in a telephoneinterview.
First, he said, more study was needed. "Then we would likethe national health agencies to look at it and see what kind ofaction is appropriate."
GETTING MORE EVIDENCE
Cogliano said this was the first time the IARC had examinedshift work as a possible cause of cancer, and said the agencywould return to the issue in perhaps five years, when moreresearch had been done.
The monograph will be published in the December issue ofThe Lancet Oncology medical journal, but the conclusions arebased on years of published research.
In 2001, a team at the Fred Hutchison Cancer ResearchCenter in Seattle found that women who work night shifts mayhave a 60 percent greater risk of breast cancer.
Several tests in mice show that circadian clock genes aredisrupted in tumor cells.
Other studies provide evidence that firefighters, whobreathe in smoke, chemicals and dust and who also work shifts,have a higher risk of cancer and heart disease.
The shift work findings may all have to do with the body'sresponse to light.
The brain's pineal gland produces the hormone melatoninafter the body is exposed to either sunlight or artificiallight and then darkness, and production is disrupted whenpeople are up at night with the lights on.
Melatonin also acts as an antioxidant protecting DNA fromthe type of damage that leads to cancer and heart disease."Melatonin does a lot about regulating the body's cycle.But I don't think we know how to tinker with the melatoninsystem ... yet," Cogliano said."We are always going to have night workers and shiftworkers. Some jobs must be done around the clock like nurses.We need to know how to reduce the risk."Other experts have pointed out that shift workers may haveother behaviors that raise cancer risk, such as a highertendency to drink alcohol or to smoke, or get less sleep.(Editing by Will Dunham and Eric Beech)