New research from the US suggests that vigorous exercise cuts the risk of breast cancer in post-menopausal women and is particularly effective for women who are not overweight.

The study was the work of researchers at the National Cancer Institute and is published in the 31 October issue of the journal Breast Cancer Research.

For the study the investigators examined data on over 32,000 women enrolled in the Breast Cancer Detection Demonstration Project Follow-up Study. This included responses to a questionnaire about their physical activity (including everyday tasks like housework, work related activity and leisure activity) over 12 months before baseline, after which incidence of post-menopausal breast cancer and deaths were monitored. The investigators then performed statistical tests to estimate the relative risk of post-menopausal breast cancer linked to physical activity.

The results showed that:

  • There were a total of 269,792 person-years of follow-up from 1987 to 1998.
  • During that time, 1,506 new incident cases of postmenopausal breast cancer were reported.
  • There was a weak inverse relationship between total physical activity and postmenopausal breast cancer (after adjusting for other possible breast cancer risk factors).
  • Vigorous activity accounted for practically all of this trend.
  • The inverse link to vigorous activity was limited to lean women (BMI less than 25 kg/m2).
  • In contrast, no link to vigorous activity was found for overweight and obese women (BMI of 25 kg/m2 and over).
  • Non-vigorous activity was not linked to breast cancer at all.
  • These results were independent of hormone receptor subtype.

The researchers concluded that for this sample, only vigorous activity appeared to reduce breast cancer risk. The result was significant for lean but not overweight and obese women and it was independent of cancer type (the hormone receptor status).

“Our findings suggest that physical activity acts through underlying biological mechanisms that are independent of body weight control,” wrote the researchers. Thus it was the exercise itself that was beneficial, regardless of whether it resulted in weight loss, they argued.

The researchers rated the following activities as “vigorous”: heavy housework like scrubbing floors and washing windows (vacuuming was rated as non-vigorous); garden digging (as opposed to general gardening); chopping wood; strenuous sports and exercise, including running, fast jogging and aerobics (as opposed to walking, golf or light jogging); cycling on hills (as opposed to on the flat); and fast dancing.

“Prospective study of physical activity and risk of postmenopausal breast cancer.
Michael F Leitzmann, Steven C Moore, Tricia M Peters, James V Lacey, Arthur Schatzkin, Catherine Schairer, Loiuse A Brinton, and Demetrius Albanes.
Breast Cancer Research, 2008, 10:R92, Published 31 October 2008.

Click here for Abstract.

Sources: Journal Article.

Written by: Catharine Paddock, PhD.