Plasma amino acids after human milk fortification and associations with growth in preterm infants.

Abstract

Background: It is unknown how plasma amino acid (AA) concentrations vary with fortification type, growth and insulin-like growth factor 1 (IGF-1) concentrations in the first weeks of life in very preterm infants (VPIs).

Methods: Human milk for VPIs (n = 225) was fortified with bovine colostrum (BC, intact proteins, high bioactivity) or conventional fortifier (CF, hydrolysed bovine whey proteins). Plasma was sampled at fortification start (T0, ~1 week of age) and after one (T1) and two (T2) weeks. Changes in Z-scores for weight, length and head circumference (HC) were calculated from T0 to 35 weeks postmenstrual age.

Results: Compared with CF, BC fortification increased 12 AAs (~10-40%, p < 0.05) and reduced Lys concentrations (10-16%, p < 0.05). Analysed across groups, T0-T2 AA increments associated positively with HC growth (12 AAs) and IGF-1 concentrations (5 AAs), and inversely with gestational age (13 AAs) and weight (8 AAs) at birth. The plasma protein profile (proteome) was unaffected by fortification.

Conclusions: BC fortification increased the plasma concentrations of many AAs. Fortification-induced AA increments associated positively with HC growth and IGF-1 concentrations, and were affected by immaturity and birth weight. Still, plasma AA variability within physiological levels appears to have limited implications for clinical outcomes during the early life of VPIs.

Impact: It is unknown how human milk fortification affects plasma amino acid concentrations, in turn influencing growth patterns in very preterm infants. We show that a fortifier based on bovine colostrum induces higher amino acid concentrations than a conventional fortifier. Fortification-induced increments in amino acid concentrations associated with gestational age, birth weight and head growth, but with small effect sizes and limited relation to body weight or length growth. Plasma amino acid concentrations are influenced by fortification of human milk in early life, but have limited practical application as predictors of body growth and health in individual very preterm infants.