Pregnancy increases a woman's risk of heart disease, stroke, and diabetes. But breastfeeding cancels out this risk, says Eleanor Bimla Schwarz, MD, assistant professor of medicine at the University of Pittsburgh.
Schwarz and colleagues analyzed data collected from about 140,000 postmenopausal women enrolled in the Women's Health Initiative. All of the women had given birth. Cumulative total duration of breastfeeding was determined for each study participant.
If women breastfed one or more months, Schwarz says, they were less likely to have diabetes, high blood pressure, or high cholesterol. If they breastfed for more than six months during their lifetime, they were less likely to have a heart attack or stroke.
"Any breastfeeding was good, but more was better," Schwarz says.
It seems to be nature's way of lessening the physical costs of having a child.
"Pregnancy without breastfeeding ups the risk of heart disease and stroke, but with breastfeeding a woman has the same risk she had before pregnancy," Schwarz says. "The more pregnancies you have, the more risk of heart disease you have. But if you breastfeed longer in each pregnancy you come out just fine."
Exactly how big is the breastfeeding effect? Schwarz and colleagues calculate that:
- For every 100 women who accumulate at least 12 months of breastfeeding over their lifetime, one case of diabetes would be prevented.
- For every 125 women who accumulate 12 months of breastfeeding, one case of heart disease would be prevented.
"The interesting finding in this study is that even when you take women's body weight into account, there still seems to be an important association between breastfeeding and long-term health effects," says Erica P. Gunderson, PhD, a research scientist at Kaiser Permanente Northern California.
Gunderson, who was not involved in the Schwarz study, points to previous studies showing that breastfeeding cuts a woman's diabetes risk.
Her own studies show that years after weaning their children, women who breastfeed for at least three months have fewer risk factors for diabetes and heart disease, including smaller waist circumference.
Belly Fat and Pregnancy
A smaller waist may be a clue to how breastfeeding reduces a woman's risk of heart disease and stroke.
In a 2008 study, Gunderson and colleagues showed that childbearing increases a woman's belly fat, regardless of how much a woman weighed before pregnancy.
Belly fat is a known risk factor for the metabolic syndrome -- a constellation of risk factors that indicate high risk for diabetes and heart disease.
"Belly fat accumulation is probably the adverse effect of pregnancy that has the most important long-term health consequences for women," Gunderson says. "This belly fat may be preferentially reduced by breastfeeding."
The American Academy of Pediatrics now recommends that women breastfeed for the sake of their children's health. Schwarz says it may be time to recommend breastfeeding for women's own health.
Gunderson says more definitive data are needed before that recommendation can be made.
"But the body of evidence is growing, and seems to consistently point to a very good effect of breastfeeding on women's health," she says.
Schwarz and colleagues report their findings in the May issue of Obstetrics & Gynecology.