Disclosures: The study was funded by the National Institutes of Health.
The longer a woman breastfeeds, the less likely she will develop metabolic syndrome over time, even if she has a history of gestational diabetes, according to the results of a prospective study that followed almost 1,400 women for 20 years.
The study appeared online in Diabetes: The Journal of the American Diabetes Association (2009: [doi.org/10.2337/db09-1197]). It will be published in the print edition of the journal in February.
“Longer duration of lactation was associated with lower incidence of the metabolic syndrome years after delivery and post weaning” among the women who had developed gestational diabetes during pregnancy and those who had not, concluded the authors, who added that these associations could not be explained by lifestyle factors. Having breastfed for more than 1 month was associated with a 39%-46% lower incidence of metabolic syndrome (depending on duration of breastfeeding) among women with no history of gestational diabetes, and with a 44%-86% lower incidence among those with gestational diabetes.
“The findings indicate that breastfeeding a child may have lasting favorable effects on a woman's risk factors for later developing diabetes or heart disease,” the lead author, Erica P. Gunderson, Ph.D., said in a statement released by Kaiser Permanente.
Their findings did not appear to be caused by differences in weight gain, physical activity, or other health behaviors, but less abdominal fat and higher levels of high-density lipoprotein were characteristic of women who did not develop metabolic syndrome, added Dr. Gunderson of the division of research, epidemiology and prevention at Kaiser Permanente, Oakland, Calif. The study followed 1,399 women enrolled in the Coronary Artery Risk Development in Young Adults (CARDIA) study, who were aged 18-30 years when they were enrolled, had never delivered a baby, and did not have metabolic syndrome at baseline. (CARDIA is a U.S. multicenter, population-based, observational study that is looking at the development of coronary heart disease risk factors in young black and white adults.)
Metabolic syndrome was defined using the National Cholesterol Education Program criteria for the diagnosis, which includes the presence of 3 of 5 characteristics that include waist girth over 88 cm, and a fasting triglyceride level of 150 mg/dL or more. Of these women, 704 had at least one singleton live birth in 1986-2006, including 84 who had gestational diabetes; over 20 years, 120 cases of metabolic syndrome were diagnosed among these women. The overall incidence of metabolic syndrome was 12.0 cases/1,000 person years. The incidence was significantly higher among those who had been diagnosed with gestational diabetes during pregnancy, than those who had not (22.1 cases/1,000 person years, compared with 10.8 cases/1,000 person years.)
“Among women with and without GDM [gestational diabetes mellitus] pregnancies, a longer cumulative duration of lactation was strongly protective, even after controlling for parity and baseline covariates, including components of metabolic syndrome before pregnancy,” the authors wrote. They noted that in previous studies, lactation has been found to have favorable effects on cardiometabolic risk factors in women with and without a history of gestational diabetes, but there have been few studies on whether these favorable effects persist and are protective after weaning.
They also pointed out that although lactation is associated with greater weight loss, changes in weight did not explain the association between lactation and metabolic syndrome that they found. More studies are needed to “elucidate the mechanisms through which lactation may influence women's cardiometabolic risk profiles, and whether lifestyle modifications, including lactation duration, may affect development of coronary heart dis ease and type 2 diabetes, particularly, among high-risk groups such as women with a history of GDM,” they wrote.