Women improve their own health outlook as well as that of their babies when they breast-feed, a major new study conducted by Oxford University in England concludes.

The study, looking back at 47 previous studies involving 150,000 women worldwide, found that the number of children women have and the length of time they breast-feed them are the most important factors influencing their chance of developing breast cancer — even more important than genetic factors.

The study, published last summer in “The Lancet” medical journal, found that if women in the industrialized world breast-fed their children six months longer than the current average two to three months, they could reduce their chance of breast cancer by 5 percent with each child.

In addition, the study found that for each child a woman bears, she reduces her risk of breast cancer by 7 percent, regardless of the number of children or the amount of breast-feeding.

Cancer protection was the same regardless of ethnic origin, drinking habits or age at menopause.

“It’s prolonging breast-feeding and having lots of children that really pushes breast cancer rates down. There are obviously other determinants, but they are much smaller,” says Valerie Beral, head of the epidemiology unit at Oxford.