'Vigorous activity' may protect against breast cancer
Breast cancer is less common amongst postmenopausal women who carry out 'vigorous' exercise, US research suggests.
A study which followed 32,269 postmenopausal women for 11 years found that those who did lots of exercise were nearly a third - 30 per cent - less likely to develop breast cancer than those who did not.
Vigorous exercise was found to reduce a woman's risk of breast cancer even if her body weight was within the normal range, indicating that lack of exercise is an independent risk factor for breast cancer.
The findings are published in the journal Breast Cancer Research and add to existing research linking a sedentary lifestyle to a heightened risk of the disease.
Dr Michael Leitzmann, who led the study at the National Cancer Institute of the US National Institutes of Health, commented: "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.
"These features enabled us to minimise any effects from other factors apart from exercise."
According to the study, the kinds of vigorous activity associated with a reduced risk of breast cancer include running, fast jogging, competitive tennis, aerobics, hill cycling and even scrubbing floors and fast dancing.
However, contrary to the findings of several previous studies, less strenuous activity such as gardening, walking, vacuuming, light jogging or recreational tennis did not appear to protect against breast cancer.
In addition, the researchers found that overweight women who did vigorous exercise did not benefit from a reduction in breast cancer risk, with activity only exerting a protective effect in lean women.
Dr Leitzmann said: "Possible mechanisms through which physical activity may protect against breast cancer that are independent of body mass include reduced exposure to growth factors, enhanced immune function and decreased chronic inflammation - variables that are related both to greater physical activity and to lower breast cancer risk."
Henry Scowcroft, science information manager at Cancer Research UK, said: "This study adds to the growing body of evidence that breast cancer is less common amongst postmenopausal women who lead an active lifestyle.
"Although this paper suggests that vigorous activity gives the most benefit, several other studies have shown that less intense activity can also be beneficial in the long run.
"Clearly, we need to do more work to find out exactly how exercise affects breast cancer risk, so that women can make informed decisions about their lifestyle."