US scientists have found that vigorous exercise may help to reduce a woman's chances of needing breast cancer treatment.
Research conducted by Dr Michael Leitzmann, from the US National Cancer Institute, found that lean women who do plenty of vigorous exercise were around 30 per cent less likely to develop breast cancer than those who were not active.
Vigorous exercise included activities such as heavy housework, running, aerobics and hill cycling.
However, less vigorous activities such as walking, light jogging and recreational tennis were found to have no beneficial effect on breast cancer risk.
The findings, which are published in the journal Breast Cancer Research, are based on a study of more than 30,000 postmenopausal women and suggest that vigorous exercise should be treated as an important way to reduce risk.
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."
According to Cancer Research UK, almost 46,000 people are diagnosed with breast cancer in the UK each year, most of whom are past their menopause.
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