Study co-author Sanne Peters, Ph.D., of the University of Oxford in the United Kingdom, and colleagues recently published their findings in the Journal of the American Heart Association.
Heart disease is the leading cause of death for men and women in the United States. The Centers for Disease Control and Prevention (CDC) report that around 610,000 people die from heart disease every year, accounting for 1 in every 4 deaths.
Stroke is one of America's leading causes of disability. Each year, more than 795,000 people in the U.S. have a stroke. Of these, around 610,000 are first-time strokes.
However, Dr. Peters and colleagues note that longer-term effects of breast-feeding on a mother's cardiovascular health remain unclear.
Breast-feeding and cardiovascular health
To get a better understanding of this association, the researchers analyzed the data of 289,573 Chinese women who were part of the China Kadoorie Biobank study. All women were free of cardiovascular disease at study baseline, and almost all of them had children.
As part of the study, the women were required to provide information on their reproductive history, including whether or not they breast-fed their children and the duration of breast-feeding.
The researchers also looked at the incidence of heart disease and stroke among the women over 8 years of follow-up.
The team found that, overall, women who had breast-fed their children were at 9 percent lower risk of heart disease and 8 percent lower risk of stroke, compared with women who had never breast-fed.
Looking at the results by breast-feeding duration, the study revealed that women who had breast-fed their children for 2 years or longer were 18 percent less likely to develop heart disease and 17 percent less likely to have a stroke, compared with non-breast-feeding mothers.
For every 6 additional months of breast-feeding, the risks of heart disease and stroke were reduced by 4 percent and 3 percent, respectively.
Metabolism 'reset' may explain findings
The researchers are unable to pinpoint the precise mechanisms behind their findings, but they speculate that the lower risk of heart disease and stroke among breast-feeding mothers may be down to a metabolism "reset" after pregnancy.
"Pregnancy changes a woman's metabolism dramatically as she stores fat to provide the energy necessary for her baby's growth and for breast-feeding once the baby is born. Breast-feeding could eliminate the stored fat faster and more completely," explains Dr. Peters.
Furthermore, the team notes that breast-feeding mothers may be more likely to adopt health behaviors that aid their cardiovascular health, compared with non-breast-feeding mothers.
While the study is observational and cannot prove cause and effect, the researchers believe that their results provide further evidence of the benefits of breast-feeding, particularly for a longer duration.
"The findings should encourage more widespread breast-feeding for the benefit of the mother as well as the child."
Senior author Zhengming Chen, University of Oxford