Women's Health: Breastfeeding counteracts cancer risk

Here's another reason why breast is best: Doctors believe breastfeeding may reduce women's cancer risk -- and the effect may be particularly important for women who have their first child after the age of 24.

Research has already demonstrated that early age at first pregnancy and having additional children are consistently associated with a reduced risk of breast tumours that contain receptors for the female hormones estrogen and progesterone. Breastfeeding is also known to reduce the risk of both hormone-receptor-positive and negative tumours.

To find out more about how age, number of children and breastfeeding interact, researchers in the United States and Australia surveyed nearly 1,000 postmenopausal women with breast cancer and 1,500 women without the disease.

As expected, women who had a first pregnancy before the age of 25 had a lower risk of developing hormone-receptor-positive breast cancer than women who had never given birth -- a protective effect that did not hold true for women who gave birth for the first time at age 25 or older.

Among women in the latter group, ever having a pregnancy was associated with more than double the risk of developing hormone-receptor-negative breast cancer, and this risk increased with additional pregnancies.

But breastfeeding protected against both types of breast cancer, regardless of when a woman first gave birth. Also, the protective effect of additional pregnancies on hormone-receptor-positive cancers was only observed among women who breastfed but not among those who never breastfed.

"In women with delayed childbirth who do not benefit substantially from the protective effects of an early pregnancy, breastfeeding may offer broad benefit," according to Dr. Giske Ursin, an associate professor of preventive medicine at the University of Southern California at Los Angeles, and her colleagues.