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UI study shows decreased risk of breast cancer in active elderly women

IOWA CITY, Iowa -- Staying active may help ward off breast cancer for postmenopausal women, according to a University of Iowa College of Medicine study that showed the more a postmenopausal woman exercised, the less likely she was to develop breast cancer.

"Several of us have been interested over the years in preventing cancer," said Dr. Robert B. Wallace, professor of preventive medicine. "The real message here is it is never too late to try to prevent a disease such as breast cancer."

The UI findings appeared in the July issue of the Journals of Gerontology Series A -- Biological Sciences and Medical Sciences. Prior to the UI study, there had been only three studies evaluating physical activity during the postmenopausal years, Wallace said. None had considered physical activity in elderly women in the context of physical function -- whether the women had disabilities that prevented them from being physically active.

"Unfortunately, some elderly cannot exercise because of arthritis or other conditions," said Wallace, who noted researchers need to identify other methods for cancer prevention among those with physical disabilities. All older women should, of course, have periodic mammograms, he added.

The UI study involved 1,806 women in Iowa. When the tracking started in late 1981, none of the women had cancer. By the time the follow-ups ended in late 1993, 46 women had developed breast cancer. Some 12 of these women had a disability, defined as an inability to perform heavy work around the house, walk up and down a flight of stairs or walk a half mile without help. Of those who were physically capable of activity, 18 women described as inactive and 14 women described as moderately active had developed breast cancer, while only two highly active women had developed the disease.

Those with breast cancer had a higher average weight, body mass index and systolic blood pressure.

"Obesity and lack of exercise are two sides to the same coin," Wallace said.

With respect to age, height, diastolic blood pressure and menstrual and reproductive history, there was no difference between those who had breast cancer and those who had never had the disease. Both groups also showed similarities in marital status, education, use of cigarettes or alcohol and the number of times they visited their doctors in the last year.

While the study did not address the underlying reason for the finding, one possible explanation might relate to insulin. Activity makes the body more insulin sensitive, meaning the body requires less insulin to do its job, Wallace said. Evidence has suggested that increased insulin levels may contribute to breast cancer. Breast cancer cell cultures showed insulin to be important in their growth and influenced the cell's movement.

The UI researchers admitted their data are limited because of the small number of incident breast cancers and the lack of information on physical activity during adolescence or adulthood, family history of breast cancer, body fat distribution and diet. However, there were several strengths to the study. The researchers relied on a population-based prospective design. They had a high participation rate and made sure they conducted complete follow-ups and in-person interviews. The researchers also used a cancer registry to ascertain breast cancer diagnoses, assessed the presence of physical disabilities, measured both recreational and home maintenance physical activity, and controlled for many of the major known breast cancer risk factors.

In addition to Wallace, the others involved in the study included these researchers in the UI department of preventive medicine and environmental health: principal researcher Dr. James R. Cerhan, formerly a UI assistant professor now practicing at the Mayo Clinic; Brian C-H Chiu, a former UI student; Jon H. Lemke, Ph.D. and UI associate professor; Dr. Charles F. Lynch, UI professor; James C. Torner, Ph.D. and UI professor; and Linda M. Rubenstein, a UI assistant research scientist.