New findings add to the evidence that exercise may help prevent cancer.
A team of researchers from the US National Cancer Institute have found that vigorous exercise may cut breast cancer risk by 13 per cent.
Dr Michael Leitzmann and colleagues followed 32,269 postmenopausal women for eleven years. They found a protective effect of vigorous activity which did not appear to be linked to body weight.
In their study, vigorous activity was defined as strenuous sports or exercise (running, fast jogging, competitive tennis; aerobics, bicycling on hills, fast dancing or heavy housework).
During follow-up 1,506 of the women developed breast cancer. Taking part in vigorous activity was linked to a 13 per cent lower risk, but the reduction was only strongly significant for women with a body mass index of less than 25. It was not specific to a certain hormone receptor subtype.
In the journal Breast Cancer Research, the authors report that no protection was found from vigorous activity for women who were overweight or obese, and non-vigorous activity showed no links to breast cancer risk.
"Our findings suggest that physical activity acts through underlying biological mechanisms that are independent of body weight control," they conclude.
Dr Leitzmann said the possible mechanisms include reduced exposure to growth factors, enhanced immune function, and decreased chronic inflammation. "Notable strengths of our study include its large sample size, prospective design, high follow-up rate, and availability of relevant known or suspected breast cancer risk factors," he added.
"These features enabled us to minimise any effects from other factors apart from exercise."
Leitzmann, M. F. et al. Prospective study of physical activity and risk of postmenopausal breast cancer. Breast Cancer Research.
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