A new study finds that regular physical activity may delay drastic preventative measures, such as a mastectomy, among women at high risk for breast cancer. The study involved 139 premenopausal women who were at high-risk for breast cancer due to either genetic mutations or family history. They were divided into three exercises groups: a “low-dose” group that performed 150 minutes of treadmill exercise per week, a “high-dose” group that exercised 300 minutes a week, and a control group that exercised for less than 75 minutes per week. After five months, the control group showed a 20% increase in estrogen-sensitive breast tissue, while the low- and high-dose groups saw reductions of estrogen-sensitive breast tissue of about 8% and 12%, respectively. The authors suggest that women who have an elevated breast cancer risk should consider performing 30 to 60 minutes of aerobic activity per day, five days per week. University of Pennsylvania School of Medicine, October 2015