MedWire News: Women with a normal body weight who partake in regular, vigorous exercise have a reduced risk for breast cancer compared with their peers who do not partake in such activity, US researchers report.

The findings show that a sedentary lifestyle can be a risk factor for the disease even in women who are not overweight.

To investigate the influence of exercise on the risk of breast cancer in older women, Michael Leitzmann (National Cancer Institute, Bethesda, Maryland) and team studied data on more than 36,000 women enrolled in a long-term health study that began in 1987.

All of the women completed questionnaires on their activity levels at the start of the study and were monitored until 1998, by which time 1506 had been diagnosed with postmenopausal breast cancer.

The researchers found that women who engaged in regular vigorous activity such as heavy housework (scrubbing floors, washing windows, digging, chopping wood), or strenuous sports or exercise were around 30% less likely to develop breast cancer than their more sedentary counterparts.

However, further analysis revealed that vigorous activity was only protective against breast cancer in lean women and not in those who were overweight or obese.

Contrary to the results of previous studies, non-vigorous activity, such as light housework (vacuuming, washing clothes, painting, general gardening) and light sports or exercise did not appear to protect against postmenopausal breast cancer.

Writing in the journal Breast Cancer Research, Leitzmann and team conclude: “In this cohort of postmenopausal women, breast cancer risk reduction appeared to be limited to vigorous forms of activity.”

They add: “Our findings suggest that physical activity acts through underlying biological mechanisms that are independent of body weight control.”

Full free text