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Study Ties Colon Cancer to Night Work

Posted on: Wednesday, 4 June 2003, 06:00 CDT

By Adam Marcus, HealthScoutNews Reporter

HealthScoutNews -- In the latest link between health problems and the graveyard shift, new research finds women who work nights may increase their risk of developing colorectal cancer.

The study found nurses who took regular night shifts were about a third more likely to be diagnosed with colorectal tumors as those who did so less frequently or not at all.

One explanation for the connection may rest with the hormone melatonin. This molecule has been shown to squelch intestinal cancers in lab animals, but it's not produced when people are exposed to light at night.

The scientists admit the effect is modest -- if it truly exists. The study doesn't prove a connection, and no one has demonstrated melatonin's anticancer properties in humans.

"This is one study and the increase is quite modest," says Francine Laden, an epidemiologist at Harvard Medical School and a co-author of the study. "More work needs to be done to look at the potential risk."

Dr. Eva S. Schernhammer, a Harvard physician and leader of the research group, says if the results hold in future studies the cancer risk might warrant a reconsideration of night work. "It would be an easy fix," she says. A report on the findings appears in the June 4 issue of the Journal of the National Cancer Institute.

Roughly 5 percent of American adults, or about 15.5 million people, work evening or irregular shifts, according to a 1997 report from the U.S. Department of Labor.

Night shifts have long been known to increase the risk of fatigue-related harm, such as car accidents and workplace injuries. But more recent evidence has suggested that scrambling one's schedule can also hike the odds of other ailments, including heart disease and breast cancer in women.

The latest work used data from the Nurses' Health Study, which originally included 122,000 women in the United States. Of those, about 78,500 provided information about their work habits. They were broken into eight groups: from those who worked no night shifts to those who worked at least three night shifts a week for 30 years or more.

Women who worked 15 or more years of night shifts were 35 percent more likely to develop colorectal cancers than those whose jobs required more day work.

Nurses who reported more night shift work were heavier, more likely to be smokers, tended to be older, and had less education, in general, than other women in the study. Each could help explain their increased risk of colorectal cancer.

But even after accounting for these factors, the researchers say, working more nights drove up the risk of developing colorectal cancer. Schernhammer says men who work nights also would be more prone to colorectal cancer.

The link between night work and cancer might be tenuous, but there are steps you can take now to reduce your risk of colorectal cancer.

"There are a number of lifestyle factors that do make a difference," says Melanie Polk, director of nutrition education at the American Institute for Cancer Research. "One is diet, another is physical activity, and another is obesity."

Eating a vegetable-rich diet low in red meat can prevent colon tumors, while exercising often and keeping a healthy weight are also protective, she says. Alcohol consumption also raises the risk of the disease, so cutting back on booze can help avoid it.

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On the Net:

National Institutes of Health

U.S. Centers for Disease Control and Prevention

Harvard Medical School

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