After eight years of follow-up, there were 16,671 cases of coronary heart disease which includes heart attacks, and 23,983 stroke cases among the 290,000 women who had no previous history of cardiovascular disease when enrolled in the study.

The researchers found that compared to women who had never breastfed, mothers who breastfed their babies had a nine percent lower risk of heart disease and an eight percent lower risk of stroke.

Among mothers who breastfed each of their babies for two years or more, heart disease risk was 18 percent lower and stroke risk was 17 percent lower than among mothers who never breastfed.

Each additional six months of breastfeeding per baby was associated with a four percent lower risk of heart disease and a three percent lower risk of stroke, the researchers said.

"Although we cannot establish the casual effects, the health benefits to the mother from breastfeeding may be explained by a faster 'reset' of the mother's metabolism after pregnancy," said study co-author Sanne Peters, research fellow at the University of Oxford.

"Pregnancy changes a woman's metabolism dramatically as she stores fat to provide the energy necessary for her baby's growth and for breastfeeding once the baby is born. Breastfeeding could eliminate the stored fat faster and more completely," Peters added.