This article originally appeared on Time.
A strong body of evidence supports the benefits of breastfeeding both for baby and mom. Breast milk gives babies a starter population of bacteria- and virus-fighting cells from their mothers, and breastfed babies tend to develop stronger immune systems, have less asthma and allergies and have fewer ear infections and respiratory problems than babies who aren’t breastfed. Some data even suggests that breastfeeding can contribute to higher IQs and better body weight among babies as they get older.
For moms, breastfeeding can help them lose pregnancy weight and lower risk of certain cancers, including breast and ovarian. Now, a new study published in the Journal of the American Heart Association adds to those maternal benefits by showing that breastfeeding may help mothers lower their risk of heart attack and stroke even a decade after giving birth.
The study involved nearly 290,000 women in China who provided information on how many children they had, whether they breastfed and for how long. The researchers followed the women for nearly 10 years looking for heart events.
Women who breastfed their babies had a 9% lower risk of having heart disease during the study period compared to women who did not breastfeed. The effect seemed to be cumulative: Women who had more than one child and breastfed each of their babies for two years or more lowered their risk of heart disease by 18% and their risk of stroke by a similar amount, compared to mother who never breastfed. Even after the researchers adjusted for factors that can influence heart events, such as cholesterol levels, blood pressure, smoking, obesity and physical activity, the effect remained strong.
The finding only points to a strong association between breastfeeding and lower heart disease risk; it doesn’t imply that women who don’t breastfeed will necessarily develop heart problems.
More research is needed to clarify the link. But breastfeeding may affect heart risk by changing the metabolism of women after they give birth, says study co-author Sanne Peters, a research fellow in epidemiology at the University of Oxford in England. During pregnancy, the body accumulates and redistributes fat in an effort to ensure the developing baby has enough nutrients and to prepare to nurse the baby with breastmilk. Previous studies suggest that the accumulated fat is more efficiently lost during breastfeeding.
“Women who don’t breastfeed essentially have metabolic reserves that they don’t need,” says Peters. That may contribute to more weight gain and raise risk factors for heart disease, such as atherosclerosis and cholesterol.
It’s not clear yet whether there is an ideal length of time to breastfeed in order to gain the greatest benefit for heart health, but future studies may answer that question, Peters says. In China, the average time that women breastfeed is longer—about a year—than for women in the West, who generally breastfeed for four to six months.
Additional studies could also shed more light on why, exactly, breastfeeding helps moms’ hearts. The current study did not find any differences in body mass index, a measure of body weight, among breastfeeding and bottle-feeding moms. But Peters says that other measures, including blood sugar, blood pressure and cholesterol levels, could provide more information on the connection.