Researchers found that regular moderate exercise such as housework provides greater protection from the disease than more strenuous but less frequent sporting activity.
Around 44,100 cases of breast cancer are diagnosed in the United Kingdom UK every year and more than 12,400 women die from the disease. Physical activity and maintaining a healthy weight have also been found to reduce the risk of some cancers in men.
Previous studies have identified a link between exercise and reduced breast cancer risk in post-menopausal women, but this is one of the first to include a large number of pre-menopausal women.
The researchers analysed data on work, leisure and housework activity levels among 218,169 women aged 20 to 80 from nine European countries including the UK.
They followed the women for an average of 6.4 years, during which time 3,423 developed breast cancers. When all forms of activity were combined, being active appeared to offer a protective effect only to post-menopausal women.
However when the results were examined in more detail it was found that women who did the most housework had significantly reduced risks, while work and recreation based activity had less effect.
On average, the pre-menopausal participants spent 17.7 hours a week doing housework while the post-menopausal women spent 16.1 hours a week on it.
Writing in the January edition of the journal Cancer Epidemiology Biomarkers and Prevention, Dr Petra Lahmann of the Medical Research Council’s Human Nutrition Research unit in Cambridge, said: “Increased non-occupational physical activity and, in particular, increased household activity, were significantly associated with reduced breast cancer risk, independent of other potential risk factors.