Women who breastfeed have a decreased risk of developing breast cancer.
The Harvard Nurses' Study, which is one of the largest and most comprehensive studies of female health ever conducted, has found that women who say they consume three or more glasses of milk per day are 30% more likely to develop invasive breast cancer over the course of the study.
Women who are breastfeeding experience significant hormonal changes, including reduced estrogen levels. A woman's body typically produces less estrogen when they're breastfeeding which reduces cell growth and division.
Many women tend to eat more nutritious foods and follow healthier lifestyles (limit smoking and alcohol use) while breastfeeding. A healthier lifestyle overall reduces risks of many diseases including cancers.