A new study from France found postmenopausal women who walked at least four hours a week over the past four years were 10 percent less likely to develop invasive breast cancer than women who exercised less.
But keeping this level of activity was key. The effect was found only in women who exercised consistely over four years.
Women who exercised earlier in life but were less active over the past four years had no decreased risk.
The study was published in the journal Cancer Epidemiology, Biomarkers & Prevention.