In general, mothers with diabetes using insulin may nurse their infants. Limited information on the newer biosynthetic insulins (i.e., aspart, detemir, glargine glulisine, lispro) indicates that they are probably secreted into breastmilk. Insulin is a normal component of breastmilk and may decrease the risk of type 1 diabetes in breastfed infants. Pasteurization of milk by the Holder method reduces the concentration of insulin in milk by about half..
Insulin requirements are reduced postpartum in women with type 1 diabetes. In one study, insulin requirements were lower than prepregnancy dosage only during the first week postpartum: 54% of prepregnancy dosage on day 2 and 73% on day 3 postpartum. On day 7 postpartum, insulin dosage returned to prepregnancy requirements. Another study found that dosage requirements did not return to normal for up to 6 weeks in some mothers. A third study found that at 4 months postpartum, patients with type 1 diabetes who exclusively breastfed had an average of 13% lower (range -52% to +40%) insulin requirement than their prepregnancy requirement. Breastfeeding appears to improve glucose postpartum glucose tolerance in mothers with gestational diabetes mellitus and in normal women.
A small, well-controlled study of women with type 1 diabetes mellitus using continuous subcutaneous insulin found that the average basal insulin requirement in women with type 1 diabetes who breastfed was 0.21 units/kg daily and the total insulin requirement was 0.56 units/kg daily. In similar women who did not breastfeed, the basal insulin requirement was 0.33 units/kg daily and the total insulin requirement was 0.75 units/kg daily. The 36% lower basal insulin requirement was thought to be caused by glucose use for milk production.
Lactation onset occurs later in patients with type 1 diabetes than in women without diabetes, with a greater delay in mothers with poor glucose control. Mothers with type 1 diabetes also discontinue nursing at a higher rate during the first week postpartum. Once established, lactation persists as long in mothers with diabetes as in mothers without diabetes. However, as in women without diabetes, smoking has a strong negative impact on lactation among mothers with type 1 diabetes. Other factors that have been identified as causes of shorter duration of breastfeeding among type 1 diabetic patients are more frequent caesarean sections and earlier delivery.
Insulin is normally present in breastmilk. In one study, insulin levels in milk were 60 milliunits/L (range 6.5 to 306 milliunits/L) in 42 mothers without diabetes who had full-term infants between 3 and 30 days postpartum. Insulin levels averaged 59 milliunits/L on day 3 postpartum and 40 milliunits/L on day 7 postpartum in 24 mothers without diabetes who had full-term infants. Mothers of preterm infants had nonsignificant changes in milk insulin levels.
Insulin was measured in donor milk from 34 nondiabetic women who were between 1 month and 1 year postpartum. The average insulin concentration was 163 picomoles/L. After pasteurization using the Holder method (62.5 degrees C for 30 min), the average concentration was 88 picomoles/L.
A small study measured breastmilk insulin concentrations in control mothers (n = 5; 1 to 6 months postpartum), mothers with type 1 diabetes mellitus (n = 4; 2 to 5 months postpartum) and type 2 diabetes (n = 5; 5 to 6 months postpartum). No differences were found in the insulin content among the 3 groups and little circadian variation was found. Mothers with type 1 diabetes were well controlled on insulin aspart and insulin glargine. No endogenous insulin was found in their breastmilk, but the milk of 3 of the mothers contained an average 20.5 milliunits/L of insulin, presumed to be of exogenous origin. No indication of paracellular diffusion of insulin was apparent in these women and C-peptide levels in milk were only 5 to 7% those of control mothers. These findings indicate that insulin is likely actively transported into breastmilk.
Relevant published information was not found as of the revision date.
Effects in Breastfed Infants:
Relevant published information was not found as of the revision date. Insulin in breastmilk is thought to be necessary for intestinal maturation of the infant and may help decrease the risk of contracting type 1 diabetes in breastfed infants.
Possible Effects on Lactation:
Proper insulin levels are necessary for lactation. Good glycemic control enhances maternal serum and milk prolactin concentrations and decreases the delay in the establishment of lactation that can occur in mothers with type 1 diabetes.
One-hundred two of 107 consecutive mothers with type 1 diabetes mellitus who delivered were followed at a Danish hospital. Mothers were given prenatal information on breastfeeding and were offered postnatal counseling by a nurse on the benefits of breastfeeding. All infants were admitted to the neonatal intensive care unit at about 2 hours of age for the following 24 hours. When possible, mothers either breastfed or pumped milk for their infants during this time. Mothers were contacted at 5 days and 4 months postpartum to determine their breastfeeding status. The rates of initiation of exclusive and nonexclusive breastfeeding and exclusive formula feeding and the rates at 4 months postpartum were no different from those of the Danish population.
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