The chances of developing breast cancer can be cut by almost a third with regular vigorous exercise, a study has found.
After following the progress of 32,269 women over a period of 11 years, scientists concluded that vigorous activities lowered the risk of breast cancer by around 30% – but not if women were overweight.
These included running, fast jogging, competitive tennis, aerobics, hill cycling and fast dancing.
"Heavy" house and garden work such as scrubbing floors, washing windows, digging, and chopping wood, were also classified as "vigorous activity".
Activities classified as "nonvigorous" did not offer the same benefits, according to the study published in the journal Breast Cancer Research. Around the home, these included vacuuming, washing clothes, painting and general gardening. They also included mild forms of exercise such as walking, light jogging, recreational tennis, and bowling.
Study leader Dr Michael Leitzmann, from the National Cancer Institute at the US National Institutes of Health, 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."