Longitudinal Variation of Amino Acid Levels in Human Milk and Their Associations with Infant Gender.

Joris Van Sadelhoff,Bert Van De Heijning,Edmond Rings,Johan Garssen,Anita Hartog,Sonia Amodio,Bernd Stahl,M Mearin

doi:10.3390/nu10091233

Abstract

It is discussed that specific amino acids (AAs) have functional roles in early life. Understanding the AA composition in human milk (HM) during lactation assists in specifying these roles. To this end we assessed the levels of free AAs (FAAs), total AAs (free and bound, TAAs) and protein levels in HM in the first 6 months of lactation, and evaluated possible associations with infant gender. HM samples of 25 healthy Dutch mothers participating in the PreventCD study were collected monthly during the first 6 months of lactation. Of the participating mothers, 12 gave birth to a boy and 13 gave birth to a girl. Analyses of the HM samples revealed that levels of free glutamate, glutamine, aspartate, glycine, and serine significantly increased during months 1–3 of lactation, both in absolute sense and relative to TAA levels. Evaluation of gender differences by mixed model analyses revealed an association between female infant gender and higher protein content (p = 0.0465) and TAA content (p = 0.0362) in HM during the first 3 months of lactation. Furthermore, there was a tendency for an association of male infant gender with higher levels of free glutamine (p = 0.0948) in HM during the first 3 months of lactation. These results show that FAA, TAA and protein levels in HM display a time-specific occurrence during lactation. Moreover, although confirmation is necessary in view of the small sample size, this study indicates that the AA composition in HM shows differential effects of the infant’s sex.

Highlights

Human milk (HM) is the best source of infant nutrition providing the energy, nutrients, and non-nutritive factors for an optimal growth and development
Significant increases of individual FAAs were found for non-essential amino acids (NEAAs) aspartate, glutamate, glutamine, glycine and serine in the first 3 months of lactation
Most of the essential amino acids (EAAs) levels remained stable along the study period, only threonine and histidine levels showed a slight but significant increase and decrease in the first 3 months of lactation, respectively (Table 2)

Summary

Introduction

Human milk (HM) is the best source of infant nutrition providing the energy, nutrients, and non-nutritive factors for an optimal growth and development. Breastfeeding is shown to have beneficial effects on the infant beyond nutrition. It is known to support gastrointestinal development by stimulating intestinal bacterial colonization and barrier formation, and it provides immediate protection against infectious diseases [1,2]. The significant effects of breastfeeding on infant health and development urge the need to define and understand the composition and functionality of HM. Proteins make up a significant part of the macronutrient composition of HM and contribute to its unique activity. Most of the proteins in HM are digested to provide the infant with an adequate supply of amino acids (AAs), which is critical for a normal growth and development [6]. AAs are released from milk proteins, HM contains free (i.e., not part of protein) AAs (FAAs), for reasons not well understood [7]

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