Women with normal blood pressure during pregnancy and who breastfed their babies for at least six months following birth had better markers of cardiovascular health years later compared to women who never breastfed, based on research presented at the American College of Cardiology's 67th Annual Scientific Session. The same benefits were not observed in women who had high blood pressure during pregnancy.
Previous studies have suggested women derive short-term health benefits from breastfeeding. While some studies have looked at outcomes much later in life, this new study is the first to assess how breastfeeding affects markers of heart health in younger and middle-aged women, about a decade after having children. The study bolsters evidence of the benefits of breastfeeding among women with normal blood pressure during pregnancy and is the first to specifically examine whether these benefits are also seen in women with high blood pressure during pregnancy.
"The study adds to the evidence that lactation is important not just for the baby but for the mother," said Malamo Countouris, MD, a cardiology fellow at the University of Pittsburgh and the study's lead author. "Breastfeeding seems to be cardioprotective in these women, as evidenced by improved cholesterol and markers of subclinical cardiovascular disease."
Study participants included 678 women who were recruited at more than 52 clinics across Michigan between 1998 and 2004. The women were pregnant at the time they enrolled in the study. They then participated in a follow-up health assessment seven to 15 years later (just over 11 years on average).
During the follow-up assessment, participants reported on how long they had breastfed after each pregnancy and researchers measured the women's blood pressure, cholesterol, triglycerides, and the diameter and thickness of the carotid artery. These factors are commonly used to assess heart disease risk because they provide early warning of potential problems in patients who do not yet have heart disease.
In their analysis, the researchers divided the women into three groups: those who never breastfed (157 women), those who breastfed for less than six months per pregnancy (284 women), and those who breastfed for six months or more per pregnancy (133 women). They separately analyzed women who had high blood pressure during pregnancy and those who had normal blood pressure during pregnancy.
On average, women who breastfed longer were older, had a lower body mass index and had a higher socio-economic status. After adjusting for these and other potential confounding factors, the researchers found that women with normal blood pressure during pregnancy who breastfed for six months or more had significantly higher levels of HDL, or "good" cholesterol, lower triglycerides and healthier carotid artery thickness compared to those who had never breastfed.
The findings suggest women may be able to reduce their risk of heart disease by breastfeeding for at least six months per pregnancy. Though the specific physiological mechanisms are not known, Countouris noted that one hypothesis is that breastfeeding increases expression of the hormone oxytocin, which can lower blood pressure. It has also been hypothesized that lactation could counteract some of the metabolic changes that occur during pregnancy.
"There's a lot we still don't understand about the accumulation of cardiovascular risks in women," Countouris said. "Examining how pregnancy may increase or perhaps mitigate some of that risk can give us insights into the unique presentation and development of heart disease risk in women."
Researchers found no evidence of cardiovascular benefit from breastfeeding among women who had high blood pressure during pregnancy. Countouris said that the number of study participants with high blood pressure during pregnancy may have been too small to reveal any potential cardiovascular benefit of breastfeeding among these women.
One limitation of the study is that researchers relied on self-reporting by study participants for information about high blood pressure or preeclampsia, a pregnancy disorder marked by high blood pressure and protein in the urine and a known risk factor for heart disease, that occurred in subsequent pregnancies after the one in which the initial data was collected. Future studies that include more participants or that track women for a longer period could help illuminate the factors that contribute to cardiovascular risk among women with normal and high blood pressure during pregnancy, researchers said.