Scientists studied more than 32-thousand normal-weight post-menopausal women for 11 years.
The women who performed heavy housework or performed strenuous workouts such as running or aerobics were 30-percent less likely to develop breast cancer.
This compared to women whose regular activity included light housework or less strenuous exercise.
Their study shows a link between a sedentary lifestyle and breast cancer.
They also say if a woman is overweight or obese, vigorous exercise won't cut down her chance of breast cancer.