Associations between human breast milk hormones and adipocytokines and infant growth and body composition in the first 6 months of life

Background: Much is to be learnt about human breast milk (HBM). Objectives: The purpose of this study is to extend our knowledge of HBM by investigating the role of maternal body mass index (BMI), sex and stage of lactation (month 1 vs. 6) on HBM insulin, glucose, leptin, IL-6 and TNF-α and their associations with infant body composition. Methods: Thirty-seven exclusively breastfeeding infants (n = 37; 16♀, 21♂), and their mothers (19–47 kg m⁻²) were studied at 1 and 6 months of lactation. Infants had body composition measured (using dual-energy X-ray absorptiometry) and HBM collected. Results: A significant interaction between maternal BMI and infant sex on insulin levels (p = 0.0322) was observed such that insulin was 229% higher in obese mothers nursing female infants than in normal weight mothers nursing female infants and 179% higher than obese mothers nursing male infants. For leptin, a significant association with BMI category was observed (p < 0.0001) such that overweight and obese mothers had 96.5% and 315.1% higher leptin levels than normal weight mothers, respectively. Leptin was also found to have a significant (p = 0.0004) 33.7% decrease from months 1 to 6, controlling for BMI category and sex. A significant inverse relationship between month 1 leptin levels and infant length (p = 0.0257), percent fat (p = 0.0223), total fat mass (p = 0.0226) and trunk fat mass (p = 0.0111) at month 6 was also found. No associations or interactions were observed for glucose, TNF-α or IL-6. Conclusions: These data demonstrate that maternal BMI, infant sex and stage of lactation affect the compositional make-up of insulin and leptin.