Mobilizing mothers' fat
Those breastfeeding benefits accrue in part because nursing can start to break down some of the fat that accumulates in women's bodies during pregnancy. At first, some mothers despair for their figures because having children generally leads to thicker midsections and thighs as women's bodies change to nourish a developing fetus and boost stores for feeding the baby once it is born. Although not optimal for long-term health, this extra weight serves an important evolutionary function.
"Clearly the woman's body is positioning itself to be able to put out an extra meal for another body, and it just takes saving calories," Schwarz explains. Producing milk for a single infant requires about 480 extra calories a day. Various analyses have come back with different information of the ability of breastfeeding to help women slim down more quickly after pregnancy. New research presented in March from Schwarz and Candace McClure, a postdoctoral researcher at the University of Pittsburgh's Department of Epidemiology, found that women who had not breastfed had an average of about seven and a half additional centimeters of fat around their waists (as gleaned from CT scans).
But as Schwarz points out, "not all body fat is created equal." The fat that tends to accumulate during pregnancy is in part visceral fat, which sits around organs in the midsection and can put people more at risk for heart and other types of diseases. Their CT study also found that, of the 351 women aged 45 to 58, those who had children and not breastfed had 28 percent more visceral fat than those who had consistently breastfed.
Lactating women appear to be better at mobilizing these new fat stores than new mothers who are using formula. And not shedding those extra post-pregnancy pounds may put women at risk for complications in later pregnancies as well as metabolic syndrome and related health problems, Stuebe and colleagues noted in a January 2009 review article published in the American Journal of Perinatology.
One big concern about these additional fat stores is their potential role in upping chances for diabetes later in life. Pregnancy itself can decrease glucose tolerance and raise insulin resistance, hence the prevalence of gestational diabetes. But research is accumulating to suggest that the process of lactation works to re-establish the balance of these key sensitivities. According to a cohort analysis by Stuebe et al., the longer a woman had lactated during her reproductive years, the less likely she was to get type 2 diabetes, regardless of BMI, which can be a risk factor for the disease.
Women who develop gestational diabetes are generally thought to be at higher risk for developing regular diabetes later in life. But new research has shown that this increased risk is significantly lessened for women who breastfeed for more than nine months, Schwarz points out. She adds that being able to tell women who have had gestational diabetes that breastfeeding will lower their chances of getting diabetes later has given her and many of her patients renewed hope for their future health.
Helping heart health
Breastfeeding helps mothers' cardiovascular health in very specific ways, Schwartz found in her analysis of postmenopausal women.
"Women who reported longer histories of lactation had significantly lower rates of risk factors for cardiovascular disease, even after adjusting for sociodemographic and lifestyle variables, family history and BMI category," Schwarz and her colleagues concluded in their May 2009 analysis. In fact, those who had breastfed for more than 12 months were about 10 percent less likely to develop cardiovascular disease compared with women who had not breastfed.
Recent research has shown aortic calcification, a risk factor for stroke, heart attack and other cardiovascular complications, was "significantly more likely" to be found in mothers who had not breastfed than in those who had for at least three months—even after adjusting for lifestyle, family history, socioeconomic status, BMI and other health issues, according to a study led by Schwarz that was published in January 2010 in Obstetrics & Gynecology.
Schwarz and others are still trying to figure out why not nursing might lead to hardened arteries and other cardiovascular risk factors. One possible explanation hinges on cholesterol levels, which increase during pregnancy. For mothers who do not breastfeed, levels of triglycerides seem to take longer (by about three months) to reach pre-pregnancy levels. Nursing mothers also seemed to have higher levels of high-density lipoprotein (HDL, or so-called "good cholesterol") while they were breastfeeding. But these shorter-term effects do not entirely clear up some of the questions surrounding heart disease later in life.
Better long-term heart health for breastfeeding mothers might stem in part from blood pressure, which was "significantly higher" in mothers who had not breastfed than in those who had (120 mmHg and 115 mmHg, respectively), according to the 2010 Schwarz study. Research has suggested that one in 29 cases of postmenopausal hypertension could be avoided if mothers breastfed for at least 12 months during their reproductive years.
Risks for cardiovascular disease in lactating versus non-lactating mothers seem to be firm regardless of BMI, which is usually a factor for both conditions. This finding "indicates that lactation does more than simply reduce a woman's fat stores," Schwarz and her colleagues wrote in their May 2009 paper. They proposed that hormonal stimulation is likely playing a substantial role.
The neurotransmitter oxytocin, which is released during nursing, seems to help women get to that "blissed-out state" many women have while breastfeeding, Stuebe says. And this relaxed state of mind can help women cope with all the stresses "that go with being a new mom." Simply getting the body in the habit of releasing this hormone by frequent nursing can pay off long after weaning. "Moms who breastfeed over long times get really good at releasing oxytocin" at other times, which activates the parasympathetic nervous system and can help alleviate stress later in life, Stuebe says.