The authors in the study report information already demonstrated by previous research including that 5-9% of pregnant women in the US develop GDM, and these women have a 7 times higher risk of developing DM than women who did not have GDM. Lactation improves glucose and lipid metabolism as well as insulin sensitivity. These have favorable metabolic effects that persist after weaning.
The authors wanted to confirm this connection that has often been assumed by looking to see if women who breastfed more exclusively and for longer would be less likely to develop DM within the 2 years after giving birth. They enrolled over 1000 pregnant women with GDM from 2008-2011. All the women were receiving care at a Kaiser Permanente clinic and hospital. After delivery they asked the women to keep track of how much they were breastfeeding, and if giving formula, how many ounces daily. They also did glucose tolerance testing on the mothers to look for DM.
They found that women who breastfed for at least 6-9 weeks had at 36-57% risk reduction for developing DM in the first 2 years after delivery when compared with women who did not breastfeed for that long. This result was independent of obesity and gestational glucose tolerance.
The authors hypothesize that the reduced risk of DM for mothers with GDM who breastfeed may be because of pancreatic β cells. These cells in the pancreas can compensate for insulin resistance. The hormone prolactin increases the mass and function of these cells during pregnancy, and there is some evidence from studies with mice that these effects continue into lactation. So prolactin may be causing an increase in the number, function and activity of pancreatic cells, helping the body to be able to produce more insulin.
Towards the end of the podcast, Drs Eglash and Bodnar discuss how more and more research is coming out demonstrating the crucial role insulin plays in lactation. They also talk about their experience with differences between women with Type I DM and Type II DM and lactation. The say that women with Type I DM tend to produce plenty of breastmilk, and this is probably because the insulin in their blood is not bound to proteins the way it is in women with Type II. They finish up by saying we have a lot more to learn about insulin and its role in lactation, and that they are very excited to learn about how prolactin affects the pancreas.
I found the podcast and the study fascinating because we all work with so many women with GDM. At WIC we are often working with pregnant mothers as they are finding out that they have GDM, and as they are making the decision of whether or not to breastfeed. Most mothers cite health reasons for the baby when saying they choose to breastfeed. Many research studies are beginning to show that mothers too benefit greatly from breastfeeding, with reduced risk of breast cancer, ovarian cancer, and osteoporosis. We are now seeing that breastfeeding reduces the risk of metabolic syndrome and also DM. This study showed reduced risk when mothers breastfed to 6-9 weeks, and they were only followed for two years. It would be exciting to see a study where mothers breastfed even longer, and were followed for 10+ years. Would a longer duration of breastfeeding have a longer term protective effect? I suspect so.
We can encourage mothers that while breastfeeding is the optimal food for their babies and the connection and bonding during breastfeeding are a wonderful part of the mother-baby relationship, breastfeeding has many health benefits for mothers as well. Benefits that will likely affect their health in a positive way decades into the future!