The relative risk of breast cancer decreased by 4.3% for every year spent breastfeeding and breast cancer risk decreased by 7.0% with each birth in this study of 150,00 women worldwide. The authors estimate that there could be half as many cases of breast cancer by having more children and breastfeeding longer.
Citation: Breast Cancer and Breastfeeding: Collaborative Reanalysis of Individual Data from 47 Epidemiological Studies in 30 Countries Including 50,302 Women with Breast Cancer and 96,973 Women Without the Disease. The Lancet. Vol. 360, Issue 9328, 2002: 187-195.