Breast-Feeding Benefits Mothers, as well as their Infants, Study Finds

Most doctors agree that breast-feeding is best for babies' health. Now a large study suggests that the practice benefits mothers as well: women who have breast-fed, it says, are at lower risk than mothers who have not for developing high blood pressure, diabetes and cardiovascular disease decades later, when they are in menopause.

The research analyzed data on some 139,681 women who had enrolled in the Women's Health Initiative, a long-term national study of postmenopausal women.

The benefits increase with duration of past breast-feeding, the study found. Women who had breast-fed for more than a year in their entire lifetimes were almost 10 percent less likely than those who had never breast-fed to have had a heart attack or a stroke in their postmenopausal years. They were also less likely to have diabetes, hypertension and high cholesterol.

The study found that even those postmenopausal women who had breast-fed for just one month had lower rates of diabetes, high blood pressure and high cholesterol, although the risk of heart disease after such limited breast-feeding was comparable to that among mothers who had never breast-fed.

The researchers estimated the prevalence of cardiovascular disease to be 9.9% in women who had not breast-fed and 9.1% in those who had. The figures were 42.1% and 38.6% for hypertension, 5.3% and 4.3% for diabetes, and 14.8% and 12.3% for hyperlipidemia. About 30% in each group were estimated to be obese by BMI of 30 or greater. Through a median of 7.9 years of follow-up during the study, duration of lactation was significantly associated with a reduction in incident cardiovascular disease among women ages 50 to 59 at baseline only (P=0.001 for trend).

Dr. Eleanor Bimla Schwarz, assistant professor of medicine at the University of Pittsburgh and chief author said, of breast-feeding, "We've known for a long time that it's important for the baby's health, but we now know it's important for mother's health as well."

Other experts cautioned, however, that while the study demonstrated an association between breast- feeding and health benefits, there was not necessarily a causal relationship. Women who breast-feed may simply lead more healthful lives than those who do not, these experts said, noting that the new analysis might not have been able to account for all the differences between the two groups.

Dr. Goldberg said of the findings, "This is a nice association, but we don't know from the study what the physiological mechanism is."

If there is such a mechanism, it could lie in oxytocin, a hormone crucial to milk production. Oxytocin is known to relax blood vessels, she said, and may make them more flexible and more resistant to the buildup of plaque.

Breast-feeding is also known to play a role in healing after pregnancy, by causing uterine contractions that help restore the uterus to its original size more quickly. Further, women burn extra calories when making milk, helping them eliminate fat stores accumulated during pregnancy.

Other recent studies have suggested breast-feeding may also reduce the risk of osteoporosis and both breast and ovarian cancer, as well as Type 2 diabetes.

The authors acknowledged some limitations of the study, including the possibility of residual confounding and recall and reporting bias, the use of self-reported data, and an inability to determine how exclusively the women breast-fed their infants.

Practice Pearl:

Explain to interested patients that this was an observational study and, as such, could not establish causality.

Schwarz E, et al "Duration of lactation and risk factors for maternal cardiovascular disease" Obstet Gynecol 2009; DOI: 10.1097/01.AOG.0000346884.67796.ca.