However, I’ve heard the single biggest thing a woman can do to reduce her risk of breast cancer is to breast feed her children. The longer the better.
All the warnings are what not to do. This is one to do.
Among many other blessing and benefits, breastfeeding rapidly returns the woman's endocrine system from pregnant-normal to non-pregnant normal. The breastfeeding blood-hormone levels tends to space out pregnancies to prevent a too-hasty follow-on pregnancy, and is a wonderful restorative to the woman on every level.
Besides, babies love Mama-milk!