Human Milk Insulin is Related to Maternal Plasma Insulin and BMI - But other Components of Human Milk do not Differ by BMI

BACKGROUND: The impact of maternal BMI and insulin sensitivity on bioactive components of human milk (HM) is not well understood. As the prevalence of obesity and diabetes rises, it is increasingly critical that we understand how maternal BMI and hormones associated with metabolic disease relate to concentrations of bioactive components in HM. METHODS: This longitudinal cohort design followed 48 breastfeeding mothers through the first four months of lactation, collecting fasting morning HM samples at 2-weeks and 1, 2, 3, and 4-months, and fasting maternal blood at 2-weeks and 4-months. Insulin, glucose, adipokines leptin and adiponectin, appetite regulating hormone ghrelin, marker of oxidative stress 8OHdG, and inflammatory cytokines (IL-6, IL-8, and TNF-a) were measured in HM and maternal plasma. RESULTS: 26 normal weight (NW) (BMI=21.4±2.0 kg/m(2)), and 22 overweight/obese (OW/Ob) (BMI=30.4±4.2 kg/m(2)) were followed. Of all HM analytes measured, only insulin and leptin were different between groups - consistently higher in the OW/Ob group (leptin: p<0.001; insulin: p<0.03). HM insulin was 98% higher than maternal plasma insulin at 2-weeks and 32% higher at 4-months (p<0.001). Maternal fasting plasma insulin and HOMA-IR were positively related to HM insulin at 2-weeks (p<0.001, R(2)≥0.38, n=31), and 4-months (p≤0.005, R(2)≥0.20, n=38). CONCLUSIONS: The concentrations of insulin in HM are higher than in maternal plasma and are related to maternal BMI and insulin sensitivity. With the exception of leptin, there were minimal other differences observed in HM composition across a wide range in maternal BMI.