In women who didn't have pregnancy-related (gestational) diabetes, breast-feeding between one and five months lowered a woman's risk of developing metabolic syndrome by 39 percent, while breast-feeding for the same duration lowered the risk of the syndrome by 44 percent in women with gestational diabetes.
And, the longer a woman breast-fed, the better it was for her later health. Breast-feeding for longer than nine months dropped the risk of metabolic syndrome by 86 percent in women with gestational diabetes. Women without gestational diabetes saw a 56 percent reduction in their risk of metabolic syndrome, according to the study.
"Breast-feeding has favorable health benefits for women as well as for children. Breast-feeding may help protect women from heart disease and diabetes in the future," said the study's lead author, Erica Gunderson, an epidemiologist and research scientist at the Kaiser Permanente Division of Research in Oakland, Calif.
The benefits of breast-feeding for infants are well-documented and include lower risk of ear infections, stomach problems, respiratory illnesses, asthma, skin allergies, diabetes and sudden infant death syndrome (SIDS). For women, breast-feeding appears to lower the risk of type 2 diabetes, breast cancer, ovarian cancer and postpartum depression, according to the U.S. Department of Health and Human Services.
Metabolic syndrome arises when a group of cardiac risk factors occurs in one person. Those risk factors include: abdominal obesity, high blood pressure, low levels of HDL ("good") cholesterol, high levels of LDL ("bad") cholesterol, high triglycerides, insulin resistance, elevated markers of inflammation and a tendency for blood to clot, according to the American Heart Association. People with metabolic syndrome are significantly more likely to have or progress to heart disease and type 2 diabetes than those without it.
For the current study, the researchers recruited almost 1,400 women into a prospective, multi-center study designed to assess what factors increase the risk of coronary artery disease. At the start of the study in 1985, none of the women had been pregnant before, and none had metabolic syndrome.
The women were examined at the start of the study, and again at 7, 10, 15 and 20 years after the start of the study.
While participating in the study, 704 of the women had babies. During pregnancy, 84 women developed gestational diabetes. During the study follow-up, 120 women developed metabolic syndrome.
Of those who developed metabolic syndrome, the average duration of breast-feeding was 2.6 months, while the average time breast-feeding for women who didn't develop metabolic syndrome was seven months, according to the study.
"We found a very strong protective effect for lactation, and longer duration is associated with a greater risk reduction," said Gunderson.
Although the researchers didn't study exactly how breast-feeding could confer a benefit against heart disease so many years later, they suspect that women who breast-feed are benefiting from higher good cholesterol levels and less accumulation of belly fat. Both of these are factors in metabolic syndrome. Additionally, Gunderson said that breast-feeding helps with the metabolism of blood sugar, which may lower their levels of insulin.
And, that's probably what's protecting these women, suggested Dr. Jacob Warman, chief of endocrinology at the Brooklyn Hospital Center in New York City. "I have a feeling that insulin is the culprit," he said.
But, he noted that this study didn't measure levels of insulin, so it's difficult to know for sure.
Still, he said, if women are concerned and would like to reduce their risk even further, they should cut back on processed carbohydrates, such as those found in sweets and in white breads, cereals and pastas. "People with a high starch diet tend to have high insulin levels," he explained.
Gunderson said that women who'd like to reduce their risk of metabolic syndrome should follow health-eating guidelines, get regular exercise, and if having a baby, consider breast-feeding. "Lactation is potentially something that could have a benefit to your own health," she said.