(Reuters Health) - Breastfeeding may protect a woman from stroke later in life, and the benefit appears to increase with the length of time she nurses, a U.S. study suggests.

Postmenopausal women who said they breastfed at least one child had a 23 percent lower risk of stroke in middle and old age compared with women who had children but didn’t breastfeed, researchers found. The effect was strongest among black women, whose stroke risk was cut nearly in half with breastfeeding.

Stroke is the fourth leading cause of death among U.S. women aged 65 and older and the third leading cause among Hispanic and black women in that age group, the study’s authors note in the Journal of the American Heart Association.

“The take-home advice to new moms is that they should include breast feeding as part of their birthing plan and they should try to continue for at least six months so they and their baby can share the optimal benefits of breastfeeding,” said study leader Lisette Jacobson of the University of Kansas School of Medicine-Wichita.

“Those who cannot breastfeed should remember that there are many factors that protect against stroke, including getting enough exercise, choosing healthy foods, not smoking and keeping blood pressure, cholesterol and blood sugar under control,” Jacobson added. “So if you can’t breastfeed for some reason, you should look at these other factors.”

The researchers analyzed data from 80,191 participants in the Women’s Health Initiative, a large ongoing study that tracks the health of postmenopausal women who signed on between 1993 and 1998. All the women in the new analysis had delivered one or more children and 58 percent said they had breastfed at some point.

Among those who breastfed, 51 percent did it for one to six months, 22 percent for seven to 12 months and 27 for 13 or more months.

After accounting for risk factors such as medical and family history and age, researchers found that stroke risk got lower the longer women breastfed. Compared to women who never breastfed, stroke risk was 19 percent lower for women who breastfed for one to six months and 26 percent lower for women who breastfed for 13 months or more.

Breastfeeding appeared to have a stronger effect on minority women. Stroke risk was 48 percent lower among black women and 32 percent lower among Hispanic women than among women who never breastfed.

Nobody knows how breastfeeding might lower stroke risk, Jacobson allowed. And ultimately, the study is observational, which means that it can only prove that breast feeding is associated with lower risk of stroke as opposed to being the cause of the lowered risk.

Women who breastfeed tend to live healthier lives in general, and that may explain at least some of the apparent protection against stroke associated with breastfeeding, the study team writes.

Jacobson hopes future research will help explain how breastfeeding might make women healthier.

Sera Young shares that hope. “Over the last 30 to 40 years we’ve looked at how breastfeeding helps babies,” said Young, an assistant professor of anthropology and global health at the Institute for Policy Research at Northwestern University in Evanston, Illinois. “We’re only dipping our toe into learning what the benefits might be for moms.”

Young, who was not involved in the new study, suspects that one way breastfeeding may help women is with weight control.

Studies have shown that breastfeeding women have a lower risk of diabetes, said Dr. Katie Berlacher, director of the women’s heart program at UPMC Magee-Womens Hospital at the University of Pittsburgh Medical Center in Pennsylvania.

“This study overall adds to the increasing amount of data that suggests breastfeeding is good not just for the baby, but also for the mom,” Berlacher said.

SOURCE: bit.ly/2w3q0S0 Journal of the American Heart Association, online August 22, 2018.