"Breastfeeding offers protection against breast cancer for all women, even those who have their first full-term pregnancy later in life," says Giske Ursin, MD, PhD, associate professor of preventive medicine at the Keck School of Medicine of the University of Southern California in Los Angeles.
Ursin notes that the findings come at a time when more women are choosing to delay childbirth until their late 20s, their 30s, and beyond.
The findings were presented at the annual meeting of the American Association for Cancer Research.
Breastfeeding Protects Against Both Types of Breast Cancer
Previous research has shown that women who have their first baby after age 25 or who have fewer than four children are at increased risk for breast cancer, Ursin says.
But those studies also showed that having your first baby before that age -- or having more children -- protected against breast cancers that are fueled by hormones. This did not, however, ward off the rarer, harder-to-treat tumors that are not fueled by hormones, Ursin tells WebMD.
The new study shows that women who first gave birth after age 25 were about twice as likely to have either type of breast cancer as women who never gave birth.
That is noteworthy because having a lot of babies was protective only among women who began having children at an early age, results showed.
Furthermore, having a lot of babies only reduced the risk of hormone-positive cancers in women who breastfed, but not in those who never breastfed, she says.
The researchers studied 995 women with breast cancer, about three-quarters of whom had hormone-fueled tumors, and 1,498 healthy women. The women -- all participants in a study of breast cancer in white and black women -- were aged 55 or older.
Breastfeeding Helps Babies, Too
Timothy Rebbeck, PhD, a cancer researcher at the University of Pennsylvania Abramson Cancer Center in Philadelphia, notes that breastfeeding is already recommended for the sake of the baby's health. Studies show breastfed babies are less likely to develop infections, asthma, and a host of other diseases than their bottle-fed counterparts.
The new study suggests moms can improve their own health by breastfeeding as well, he tells WebMD.