The longer a woman breast-feeds her children and the more children she has, the less likely she'll be to develop breast cancer. This finding may help explain why breast cancer is more common today in developed countries than it used to be.
Valerie Beral of Radcliffe Infirmary at Oxford University in England and her colleagues analyzed data from 147,275 women who had participated in 47 studies in 30 countries. Of these women, 50,302 had breast cancer.
A woman's risk of developing breast cancer dropped by 7 percent for each child she had and decreased by 4.3 percent for every year of breast-feeding. The effects were consistent in both developed and developing countries and for women of different ages, ethnic backgrounds, and varying childbearing characteristics, Beral's team reports in the July 20 Lancet.