Background/objectives: Breastfeeding may protect against excessive weight gain during infancy. However, the breast milk components responsible for this effect are unknown. We examined the variation of three breast milk hormones (adiponectin, leptin and insulin) according to maternal characteristics and determined their association with infant body composition.
Subjects/methods: We studied a representative subset of 430 breastfed infants in the CHILD birth cohort. Breast milk was collected at 4 months postpartum and hormone concentrations were measured using the MesoScale Discovery System. Weight-for-length (WFL) and body mass index (BMI) z-scores were calculated according to the World Health Organization reference standard from infant anthropometrics measured at 4 months and 1 year. Maternal BMI and demographics were self-reported.
Results: Breast milk hormone concentrations varied widely between mothers. The geometric mean (range) was 19.4 (3.7-74.4) ngml-1 for adiponectin; 361 (31-3968) pgml-1 for leptin; and 589 (53-5557) pgml-1 for insulin. Maternal BMI was positively correlated with breast milk insulin (r=+0.40, P<0.0001) and leptin (r=+0.71, P<0.0001), but not adiponectin (r=-0.02, P=0.68). Breast milk hormone concentrations were also associated with maternal ethnicity, parity and breastfeeding exclusivity at sample collection. Independent of these factors and maternal diabetes, smoking and breastfeeding duration, higher breast milk leptin was associated with lower infant WFL z-score at 4 months (β -0.67, 95% confidence interval (CI): -1.17, -0.17 for highest vs lowest quintile) and 1 year (β -0.58, 95% CI: -1.02, -0.14). Insulin showed a U-shaped association, with intermediate concentrations predicting the lowest infant WFL z-score at 4 months (β -0.51, 95% CI: -0.87, -0.15 for third vs lowest quintile) and 1 year (β -0.35, 95% CI: -0.66, -0.04). Similar results were seen with infant BMI. Breast milk adiponectin was not significantly associated with infant body composition.
Conclusions: Breast milk hormone concentrations were associated with several fixed and modifiable maternal characteristics. Higher concentrations of leptin and intermediate concentrations of insulin were associated with lower infant WFL in the first year of life.