A new study indicates that breastfeeding may reduce the risk of breast cancer. Researchers at the University of North Carolina in Chapel Hill examined data from the Carolina Breast Cancer Study and compared the rates of breast cancer in 751 mothers who had breastfed at least once and 743 mothers who had not. The study found that the risk of breast cancer was reduced by 20 percent in women age 20 to 49 years and by 30 percent in women ages 50 to 74 years who had breastfed, compared to those who had not breastfed. Authors conclude that breastfeeding is associated with a reduction in the risk of breast cancer among both younger and older women and speculate that breastfeeding may cause structural changes in the breast that offer the protective factors. The study is in the "International Journal of Epidemiology" (1999;28:396-402).