Monday November 3, 2008 (foodconsumer.org) – Vigorous, but not moderate physical activity or exercise may reduce risk of breast cancer in postmenopausal women with normal body weight, according to a study published in the Oct. 2008 issue of Breast Cancer Research.

The study led by Michael F Leitzmann and colleagues at the National Cancer Institute found that postmenopausal women with body mass index lower than 25 kg/m2 engaged in vigorous physical activity were 23 percent less likely to develop breast cancer.   But no such association was found in overweight and obese women.

For the study, the researchers followed 32,000 women enrolled in the Breast Cancer Detection Demonstration Project Follow-up Study to examine if there was an association between risk of breast cancer and physical exercise.

Physical activity was surveyed by self-administered questionnaire and postmenopausal breast cancer cases were identified through self-reports, death certificate and state cancer registries.   During the 11-year follow-up, 1506 new incident cases of postmenopausal breast cancer were identified.

The researchers found after adjusting a variety of risk factors, there was a weak inverse association between total physical activity and postmenopausal breast cancer.

Women who were in the quintile engaged in the most vigorous physical activity were 13 percent less likely to develop breast cancer than those in the quintile in non-vigorous exercise.

But the potential protection was only observed in those who were lean.    No association between breast cancer risk and physical activity was found in women who were obese or overweight and those who were engaged in moderate or light activity.

In the study, "moderate activity (referred to as non-vigorous activity) included light housework, vacuuming, washing clothes, painting, home repairs, lawn mowing, general gardening, raking, light sports or exercise, walking, hiking, light jogging, recreational tennis, bowling, golf and bicycling on a level ground,"    Michael F Leitzmann and colleagues wrote.

"Examples of vigorous activity included heavy housework such as scrubbing floors or washing windows, heavy yard-work, digging in the garden, chopping wood, strenuous sports or exercise, running, fast jogging, competitive tennis, aerobics, bicycling on hills and fast dancing."

Physical activity has been linked to reduced risk of breast cancer in previous studies. But the conclusion from the current study differs from that from some previous studies which showed even light exercise helps reduce risk of developing breast cancer or dying from the disease.

One study led by Dr. Aditya Bardia and colleagues at the University of Iowa and presented at the annual meeting of the American Society of Clinical Oncology found that physical activity was linked to a 10 percent reduced risk of developing breast cancer in postmenopausal women.

Another study of 45,631 women by Howard R A and Leitzmann M F and colleagues from the National Cancer Institute found the greatest risk reduction (43 percent) was found among women who reported walking/hiking as exercise for 10 or more hours per week compared to those who did not do walking/hiking.   But this protective effect was offset by menopausalhormonetherapy.

The study was published in the Oct 23 2008 issue of Cancer causes & control.

In the current study led by Leitzmann and colleagues, hiking and walking were listed as moderate exercise and they were not associated with reduced risk of breast cancer.

Breast cancer is expected to be diagnosed in 185,000 women and to kill 45,000 patients in the United States each year.    One in every weight women in the country will end up diagnosed with this disease in their lifetime.    In addition to physical activity, many modifiable lifestyle and diet parameters can be changed to lower the risk.

Sources:

Michael F Leitzmann, Steven C Moore, Tricia M Peters, James V Lacey, Arthur Schatzkin, Catherine Schairer, Loiuse A Brinton and Demetrius Albanes

Prospective study of physical activity and risk of postmenopausal breast cancer

Breast Cancer Research 2008, 10:R92doi:10.1186/bcr2190 published 31 October 2008

Howard RA, Leitzmann MF, Linet MS, Freedman DM.

Cancer Causes Control. 2008 Oct 21.

Physical activity and breast cancer risk among pre- and postmenopausal women in the U.S. RadiologicTechnologists cohort.