Human Milk Hormone Intake in the First Month of Life and Physical Growth Outcomes in Preterm Infants

Context: Human milk contains hormones that regulate metabolism. Extrauterine growth restriction remains common among preterm infants, but the effect of ingesting milk hormones on preterm infant growth is poorly understood. Objective: To quantify associations of longitudinal exposure to leptin, adiponectin, and insulin in milk with physical growth of preterm infants. Design/Methods: In 50 preterm neonates (median gestational age 29.4 weeks), we sampled maternal milk on day-of-life 7, 14, 21, and 28 and measured hormone levels in whole milk by ELISA. Milk leptin levels were available for a subset of 18 infants. We calculated milk hormone doses by multiplying the hormone level by the milk volume ingested on each day and estimated the area under the curve (AUC) to reflect longitudinal exposure. We analyzed associations of milk hormone exposure with growth outcomes in generalized estimated equations. Main Outcome Measures: Weight gain velocity and z-scores in weight, length, head circumference, and body mass index at 36 weeks' postmenstrual age (PMA). Results: Higher leptin intake was associated with greater weight gain (2.17g/kg/day [95% CI, 1.31, 3.02]) and weight z-score at 36 weeks' PMA (0.30 [0.08, 0.53] higher z-score per tertile). Higher adiponectin intake was associated with greater length z-score (0.41 [0.13, 0.69]), however, this association was nullified after adjustment of protein and calorie intake. Higher adiponectin was associated with smaller head circumference z-score (-0.36 [-0.64, -0.07]). Insulin was not associated with growth outcomes. Conclusions: Milk leptin and adiponectin exposures may affect growth of preterm infants. The long-term effects of milk hormones warrant further investigation.

Automated summary

Leptin intake in milk was positively associated with weight gain and weight z-scores in preterm infants, while adiponectin intake was associated with length z-scores and negatively with head circumference z-scores after adjusting for protein and calorie intake. Insulin intake did not show significant associations with growth outcomes. Further research regarding the long-term effects of milk hormones is warranted.