The study followed 85 women who breast-fed their babies and 99 women who didn’t. The groups were similar in many ways that could impact their risk for developing type 2 diabetes: number of prior pregnancies, age, pre-pregnancy weight, blood sugar levels and glucose tolerance during pregnancy, and exercise habits.
Women Who Breast-Fed Had Improved Glucose Tolerance After 3.6 Years
Two months after delivery, both groups of women still had similar glucose tolerance, a measure of how easily the body converts sugars from food into energy. After an average follow-up period of 3.6 years, however, the groups looked much different. Compared with women who didn’t breast-feed at all, mothers who nursed their babies had better glucose tolerance and higher insulin sensitivity, which helps the body use glucose more effectively and reduces blood sugar levels. “We knew that breast-feeding had immediate effects on metabolic balance in mothers who breast-fed, and this was due in part to the energy consumption involved in breast-feeding,” says one of the study’s authors, Michael German, MD, of the University of California San Francisco. “However, it was not clear why breast-feeding had long-term benefits, reducing the risk of developing diabetes many years later,” Dr. German says. RELATED: 8 Surprising Risk Factors for Type 2 Diabetes
In Mice, Milk Production Caused More Growth of Beta Cells
To better understand what may have happened to improve glucose tolerance and insulin sensitivity in the women who breast-fed their babies, researchers next tested the effects of nursing in mice. Animal experiments suggest the hormone prolactin released by the pituitary gland to stimulate milk production also caused more beta cells to grow in the pancreas. Excess beta cells increased the ability of the pancreas to make the insulin needed to deliver nutrients to the breast. Mice typically wean their pups after about three weeks. The animals in the study had more beta cells and higher insulin production at three weeks than the mice that didn’t feed their babies. After four months, the mice feeding their babies still had higher insulin production. “The long-term benefit of this increased number of beta cells and the insulin they produce is that they reduce the risk of developing diabetes,” German says. While the mice studies were controlled experiments, researchers didn’t randomly assign women to breast-feed or formula-feed their babies in the human portion of the study. This makes it possible that some factors not measured in the analysis might explain the connection between breast-feeding and type 2 diabetes risk.
Even a Little Breast-Feeding May Lower Diabetes Risk, Prior Studies Suggest
Another limitation to the analysis in humans is that researchers didn’t examine how long women breast-fed their babies, or whether they breast-fed exclusively. Both these factors can affect how much breast-feeding reduces the risk of type 2 diabetes, previous research has found. A study published in November 2017 in JAMA Internal Medicine followed 1,238 women without diabetes before pregnancy for an average of 25 years. Compared with women who didn’t breast-feed at all, those who nursed babies for up to six months were 25 percent less likely to develop type 2 diabetes; mothers who nursed babies longer had their diabetes risk cut by more than half. Even for women at high risk for type 2 diabetes because they had gestational diabetes during pregnancy, breast-feeding was linked to a lower diabetes risk two years after delivery, according to a study published in December 2015 in Annals of Internal Medicine. In this study of 1,025 women, breast-feeding appeared to reduced diabetes risk even when women still supplemented nursing with formula. Compared with women who used only formula, women who occasionally breast-fed in addition to using formula were 36 percent less likely to develop type 2 diabetes, this study found. Mostly breast-feeding but supplementing with formula was tied to a 46 percent lower diabetes risk, while exclusive breast-feeding was associated with a 54 percent lower risk. Compared with women who did not breast-feed at all, women who breast-fed but mostly used formula were 36 percent less likely to develop type 2 diabetes, this study found. Women who fed their babies breast milk and some formula experienced a 46 percent lower diabetes risk; exclusive breast-feeding was associated with a 54 percent lower risk. While the current study in Science Translational Medicine doesn’t examine the extent of lactation, it does offer fresh insight into why earlier studies found a connection between breast-feeding and lower diabetes risk, says Lori Feldman-Winter, MD, MPH, a professor of pediatrics at Cooper Medical School of Rowan University in Camden, New Jersey. “Up to now we relied on epidemiological (observational) studies to examine the associations between breast-feeding and a reduced risk of developing diabetes among women that breast-fed,” Dr. Feldman-Winter says. “This study provides the scientific basis, and biological plausibility, that the observational studies were probably due to underlying mechanisms that are indeed explanatory.” RELATED: Pregnancy, Breast-Feeding Linked With Later Menopause, Study Says
Breast-Feeding Isn’t the Only Way to Lower Type 2 Diabetes Risk
Women who use only formula don’t need to fear that developing type 2 diabetes is a forgone conclusion. On the contrary, there are plenty of things they can do to minimize their risk, says Yukiko Washio, PhD, a breast-feeding researcher at RTI International, a nonprofit research institute. “It certainly helps to breast-feed … however, there are lifestyle interventions that women can take up such as exercising during pregnancy and postpartum to prevent diabetes and weight gain,” says Dr. Washio. Poor diet is also an important risk factor for type 2 diabetes. “Eating foods that have a lower glycemic index — lower in high fructose corn syrup and sugars — also helps,” Feldman-Winter adds. In general, whole, unprocessed foods including veggies, fruit, and whole grains, are lower on this index than those that are processed, such as potato chips, cake, and cookies. RELATED: The Best and Worst Foods for People With Type 2 Diabetes
