LAUSR

Objectives It is often cited that insulin in human milk (HM) increases postprandially along with maternal serum insulin. However, this response has never been documented in humans, and the characteristics of this increase remain unstudied. Methods Two healthy lactating women emptied their breasts after a fast (> 8 hours) using an electric breast pump. After consuming a 50g glucose water, each woman emptied a single breast at 15, 30, 60, 90, and 120 minutes. Skim milk was generated via centrifugation and HM glucose and insulin were measured via hexokinase assay and chemiluminescent immunoassay (Beckman Coulter). At each of these time points maternal blood was collected via finger prick and capillary glucose measured via handheld glucometer. Additional blood was spotted onto a dried blood spot (DBS) card, and maternal insulin was measured from the DBS cards via Ultrasensitive ELISA (Mercodia). Results Both insulin and glucose concentrations rose in HM after the glucose load (Figure A, B). The amplitudes of both HM insulin and glucose were lower than that of maternal circulation. Neither HM insulin nor glucose were correlated with concentrations in maternal blood. However insulin concentrations were tightly correlated with glucose concentrations in both HM (P < 0.0001, R2 = 0.84) and maternal blood (P < 0.001, R2 = 0.72). At 2 hours post-glucose challenge, both maternal blood insulin and glucose had returned to near fasting levels (insulin: 15.1 ± 7.8 µU/mL; glucose: 107 ± 4 mg/dL). However, HM insulin and glucose concentrations remained elevated (Figure A, B). At 2 hours, HM insulin remained 13 times higher than fasting concentrations and HM glucose remained 3.9 times higher than fasting concentrations. Conclusions To our knowledge, these are the first data in humans to characterize the time course of HM insulin response to an oral glucose challenge. These data will inform the design of HM composition studies when free-living HM samples are collected. The impact of variation in these components over the day on the recipient infant deserves further research. Funding Sources Internally Funded. Supporting Tables Images and/or Graphs