A panel of expert scientists assembled by the World Cancer Research Fund and the American Institute for Cancer Research (WCRF/AICR) reviewed existing studies on the association of physical activity and breast cancer risk, and concluded that physical activity probably has a preventive effect on postmenopausal breast cancer, but they found less evidence for a relationship between physical activity and premenopausal breast cancer. Studies on physical activity and breast cancer have reported a 20 to 40 percent lower risk of breast cancer among women who are most physically active. Physical activity levels, unlike most breast cancer risk factors, can be changed. Over a lifetime each additional hour of physical activity per week has been linked with a six percent decrease in breast cancer risk. Decreased breast cancer risk has been associated with increased physical activity in women of all but extremely high body sizes. Physical activity may help to improve survival after a diagnosis of breast cancer. Other health benefits of physical activity include decreased risk of cardiovascular disease, stroke, diabetes, arthritis and other cancers.