英国癌症研究网这样说

Breastfeeding lowers the risk of developing breast cancer, particularly if you have your children when you are younger. The longer you breastfeed the more the risk is reduced.

显然，工作压力大的年轻女性常常会晚婚晚育，有了孩子常常无法母乳喂养，所以乳腺癌风险就高。