Infant Maturity at Birth Reveals Minor Differences in the Maternal Milk Metabolome in the First Month of Lactation

Abstract

Background: Human milk is the gold standard of nutrition for infants, providing both protective and essential nutrients. Although much is known about milk from mothers giving birth to term infants, less is known about milk from mothers giving birth to premature infants. In addition, little is known about the composition and diversity of small molecules in these milks and how they change over the first month of lactation.

Objective: The objective was to understand how milk metabolites vary over the first month of lactation in mothers giving birth to term and preterm infants.

Methods: (1)H nuclear magnetic resonance (NMR) metabolomics was used to characterize metabolites that were present in micromolar to molar concentrations in colostrum (day 0-5 postpartum), transition milk (day 14), and mature milk (day 28) from mothers who delivered term (n = 15) and preterm (n = 13) infants. Principal components analysis, linear mixed-effects models (LMMs), and linear models (LMs) were used to explore the relation between infant maturity and the postpartum day of collection of milk samples.

Results: By using a standard NMR metabolite library, 69 metabolites were identified in the milks, including 15 sugars, 23 amino acids and derivatives, 11 energy-related metabolites, 10 fatty acid-associated metabolites, 3 nucleotides and derivatives, 2 vitamins, and 5 bacteria-associated metabolites. Many metabolite concentrations followed a similar progression over time in both term and preterm milks, with more biological variation in metabolite concentrations in preterm milk. However, although lacto-N-neotetraose (LMM, P = 4.0 × 10(-5)) and lysine (LM, P = 1.5 × 10(-4)) significantly decreased in concentration in term milk over time, they did not significantly change in preterm milk.

Conclusion: Overall, the metabolic profile of human milk is dynamic throughout the first month of lactation, with more variability in preterm than in term milk and subtle differences in some metabolite concentrations. This trial was registered at clinicaltrials.gov as NCT01841268.

Keywords: human milk; human milk oligosaccharides; lactation; metabolomics; preterm; term.

FIGURE 1

PCA of term and preterm milks during the first month of lactation. (A) Term milk only. (B) Preterm milk only. (C) Original PCA of all milk samples. (D) PCA colored on the basis of secretor status. PC, principal component; PCA, principal components analysis; PT, preterm; T, term.

FIGURE 2

Human milk oligosaccharides that significantly differ in concentration between term and preterm milk. Values are means ± SEMs. (A) LNFP III. P values represent the significance of postpartum day of lactation on LNFP III concentration by using an LMM (term) or an LM (preterm). (B) LNnT. P values represent the significance of postpartum day of lactation on LNnT concentration by using an LMM (term) or an LM (preterm). For term milk, the LNnT concentration was also influenced by maturity of the infant at birth (LMM, P = 3.5 × 10⁻²) and secretor status (LMM, P = 2.5 × 10⁻⁵), but none of the interaction terms were significant. For both LNFP III and LNnT: milk collected on postpartum day 0–5, n = 15 term and n = 10 preterm; milk collected on postpartum day 14, n = 14 term and n = 10 preterm; and milk collected on postpartum day 28, n = 15 term and n = 6 preterm. LM, linear model; LMM, linear mixed-effects model; LNFP, lacto-N-fucopentaose; LNnT, lacto-N-neotetraose.

FIGURE 3

Human milk amino acids that differ significantly in concentration between term and preterm milk. Values are means ± SEMs. (A) Glutamine. P values represent the significance of postpartum day of lactation on glutamine concentration by using an LMM (term) or an LM (preterm). (B) Lysine. P values represent the significance of postpartum day of lactation on lysine concentration by using an LMM (term) or an LM (preterm). Lysine concentration is also influenced by the maturity of the infant (P = 6.7 × 10⁻³) *Significant difference in mean concentration between term and preterm milk at a specific time point, P < 0.05. For both glutamine and lysine: milk collected on postpartum day 0–5, n = 15 term and n = 10 preterm; milk collected on postpartum day 14, n = 14 term and n = 10 preterm; and milk collected on postpartum day 28, n = 15 term and n = 6 preterm. LM, linear model; LMM, linear mixed-effects model.