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Jobs, Housework May Reduce Breast Cancer Risk


WASHINGTON — Women who are active on the job or doing housework have a lower risk of breast cancer, researchers say.

The busiest women had 31% less risk than those who did the least, their study found.

But although the women did have to stay active, they didn't have to work hard, said Christine M. Friedenreich, a research scientist at the Alberta Cancer Board in Calgary. "Moderate activity was related to the greatest risk reduction," she said.

Friedenreich and her colleagues looked at data on breast cancer cases in the province of Alberta from 1995 to 1997. In Canada's health care system, all cancer cases have to be reported to government agencies.

Their study looked at 1,233 women with breast cancer and 1,237 women who were healthy and who served as a comparison group. The researchers found the healthy study participants by doing telephone solicitations. Study results were reported in the September issue of the American College of Sports Medicine journal, Medicine and Science in Sports and Exercise.

The researchers asked the women to recall their physical activity over their lifetimes. To freshen the subjects' memories, the researchers also asked them to recall events from those times-- among them, school experiences and major life events such as weddings.

Women who put in more than about 43 hours a week of physical activity throughout their lives had a 31% lower risk of breast cancer than did women who put in about 29 hours or less, the study found. The study found women benefited from activity in housework or on the job, but that work carried a slightly greater benefit.

There was no significant benefit from exercise, but Friedenreich said there were too few exercisers among the women in her study to ascribe much meaning to that.

Women who don't get much activity cleaning house or at work probably would get as much benefit from an equivalent amount of energy-using exercise, Friedenreich said.

"The take-home message is that it's important to be physically active in all aspects of your life," Friedenreich said. A brisk walk of 30 to 40 minutes on most days of the week is "probably the level that people should be trying to achieve," she said.

When intensity of the activity was considered separately, women who were moderately active had a 41% lower risk of breast cancer. The study defined moderate activity as increasing the heart rate slightly and possibly creating some light perspiration.

Earlier research also has found signs that activity reduces the risk of breast cancer, but this is the first to show a benefit can be gained from housework, said Louise Brinton, chief of the environmental epidemiology branch at the U.S. National Cancer Institute.

Exercise might have caused an improvement directly or by reducing the impact of some other risk factor, such as overweight, Friedenreich said.

However, although the study found that women who did more had a lower risk of breast cancer, it does not prove that their activity caused the reduction. The possibility remains that some other, unknown factor was at work in the lives of the more active women.

"It's too early to make a firm conclusion," said Brinton, who was not affiliated with the Canadian project. "We are hopeful that the studies will emerge that this is a protective factor because we have so few modifiable factors for breast cancer."

Exercise may also affect hormones that can raise the risk of breast cancer, Brinton said. Obesity and alcohol use are among modifiable factors. But genetics plays a strong role, and much of the cause of breast cancer simply is not known.

Friedenreich's paper has several weaknesses, said Leslie Bernstein, a researcher at USC. For instance, the project did not properly account for the effect of exercise, she said. Bernstein's research found a dramatic drop in breast cancer risk among women who exercised.

But the idea that activity can reduce the risk of breast cancer sits well with Bernstein. Reducing risk factors can't prevent the disease, but studies have indicated the odds can be cut, she said.

"I'm a firm believer that physical activity is one means of reducing breast cancer risk," Bernstein said.

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