As estimated 25,000 breast cancers would be prevented in developed countries if women had the same number of children but breastfed each child for six months longer, researchers have concluded.

Scientists have known of a connection between breastfeeding and reduced rates of breast cancer since the 1920s. But it was hard to tell whether it was childbearing or breastfeeding that offered the protection.

Researchers analysed data from 47 other studies from around the world involving almost 50,000 women with invasive breast cancer and about 97,000 women without breast cancer.




They concluded that although having children decreased the risk of breast cancer, breastfeeding itself is also protective. The protection was higher the longer women breastfeed.

In developed countries like Canada, more than half of women either don't try to breastfeed, or stop before three months.

The researchers say given current breastfeeding patterns in Canada, six per cent of women will develop breast cancer. If women breastfed for at least 16 months over their lifetime, the incidence might drop to three per cent.

Dr. Cornelia Baines
Dr. Cornelia Baines

Return to century-old pattern of childbearing 'unrealistic'

"It's probably the single major factor in explaining the differences in breast cancer rates in the developing world," said one of the study's authors, Valerie Beral of Oxford University. The study appears in this week's issue of The Lancet.

Dr. Cornelia Baines is a professor of public health sciences at the University of Toronto. She said the study may be useful for epidemiologists and policy makers.

"But for the individual woman to think that by (breastfeeding) she is going to benefit herself, I think that she is not being very realistic," said Baines.

Scientists don't understand why breastfeeding protects against breast cancer. In the future, if the mechanism is understood, then therapies may be developed to mimic the effect.

Doctors say the best reason to breastfeed continues to be because it's good for the baby. But they don't want the study to add to the guilt women may feel if they can't breastfeed.