Young women who breast-feed may have healthier-looking arteries years later, compared with those who bottle-feed their babies, a new study finds.
It has long been reported that breast-feeding is the healthiest option for babies.
The study, published in the August issue of Obstetrics & Gynecology, hints at another potential health benefit from breast-feeding. But researchers also stressed that the findings do not prove cause-and-effect.
What the study did show: Of over 800 U.S. women who gave birth at least once, those who breast-fed for a longer period of time had less thickening in the carotid artery wall once they'd reached middle age.
The carotid arteries supply blood to the brain, and thickening in the artery wall is considered an early sign of atherosclerosis -- the buildup of artery-clogging "plaques" that can lead to heart attack or stroke.
Thickening in the artery walls can be viewed as "vascular aging," explained lead researcher Erica Gunderson, of Kaiser Permanente Northern California's division of research in Oakland, Calif.
In this study, she said, women with the greatest carotid artery thickening were essentially three to five years older -- in terms of blood vessel health.
But the question remains: Is the difference because of breast-feeding?
Dr. Suzanne Steinbaum, a preventive cardiologist who was not involved in the study, was not convinced.
"This is an interesting study," said Steinbaum, director of the Women's Heart Health program at Lenox Hill Hospital in New York City. "There's clearly a correlation between breast-feeding and [artery-wall thickening], but we can't be sure what it means."
She pointed out that women who breast-fed, particularly for a longer time, were generally thinner, better-educated and more physically active -- both in young adulthood and 20 years later.
Gunderson's team did account for those factors, and still found a statistical connection between breast-feeding and artery-wall thickness. But it's difficult to zero in on breast-feeding as the direct cause, Steinbaum said.
The findings are based on 846 U.S. women who, in the 1980s, enrolled in a long-term study of cardiovascular health. They were between the ages of 18 and 30 at the time.
All of the women underwent ultrasound scans of the carotid artery 20 years after entering the study.
On average, Gunderson's team found, women who had breast-fed their babies for one month, or not at all, had more thickening in the carotid artery wall. Those who had breast-fed for 10 months or longer had the clearest arteries.
Gunderson agreed that the findings show only a correlation, rather than a definite case of cause-and-effect.
She suspects, however, that breast-feeding might be beneficial through effects on body weight and, even more so, on blood pressure: When her team accounted for the study participants' weights and blood pressures in middle-age, that seemed to explain much of the connection between breast-feeding and artery health.
"That's consistent with what we'd expect," Gunderson said. When a woman breast-feeds, the body releases the hormone oxytocin, which other research has linked to lower blood pressure.
"Pregnancy is an incredibly stressful physiologic process," Gunderson said. "It puts greater demands on the cardiovascular and metabolic systems."
Breast-feeding, she said, may help "reset" those systems after pregnancy.
A big question, though, is whether breast-feeding moms actually have lower rates of heart attack and other cardiovascular problems down the road. Gunderson said her team wants to continue to follow this study group to find out.
In the meantime, since breast milk is considered the best nutrition for babies, moms already have reason to do it, Gunderson said. The potential long-term heart benefits might just offer "more motivation," she added.
At the same time, both she and Steinbaum stressed that women shouldn't feel guilty if they do not breast-feed.
Some women simply can't, because of the "demands of the workplace," Gunderson explained. Others find breast-feeding difficult, she added -- in which case they can ask their health care provider for help.
Steinbaum made another point: There are plenty of other ways for women of all ages to boost their heart health, such as eating a healthy diet, exercising regularly and not smoking.
"It's important to be heart-conscious during all parts of your life," Steinbaum said.