Women who breastfeed may have a reduced risk of developing certain types of breast cancer, a new study suggests.

The study related to two types of breast cancer, known as oestrogen-receptor negative and progesterone-receptor negative. These hormone negative breast cancers are often more aggressive and harder to treat than hormone positive cancers. They also often affect younger women.

US scientists looked at data relating to over 4,000 women with breast cancer and almost 3,000 without the disease.

They found that women who had not breastfed had an increased risk of developing these ‘negative' types of breast cancer.

"Women who had children but did not breastfeed had about 1.5 times the risk for these cancers. If women breastfed their children, there was no increased risk for them. This is particularly important as breastfeeding is a modifiable factor that can be promoted and supported through health policy," the team from Columbia University said.

The study also found that oral contraceptives did not increase the risk of these types of cancer.

Details of these findings were presented at a conference of the American Association for Cancer Research (AACR).