Researchers in France found that almost 60,000 women who had exercised for the equivalent of four hours a week were 10 per cent less likely to develop breast cancer than those who were not active.
But the effect was only found in women who exercised regularly over four years.
The study, which was published in the journal Cancer Epidemiology, Biomarkers & Prevention, supports the message that regular exercise has many health benefits.
“Twelve metabolic equivalent task-hours per week corresponds to walking four hours per week or cycling or engaging in other sports two hours per week and it is consistent with the World Cancer Research Fund recommendations of walking at least 30 minutes daily,” said Dr Agnès Fournier, a researcher in the Centre for Research in Epidemiology and Population at the Institut Gustave Roussy.
Breast cancer is the most common cancer affecting women. In 2014, it is estimated that 15,270 women will be diagnosed with breast cancer, according to the Breast Cancer Network Australia.