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

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.

Calorie intake is associated with weight gain during transition phase of nutrition in female extremely low birth weight infants

“…In summary, natural biological processes in animals provide milk with distinctively different compositions to suit the nutritional needs based on the sex of the offspring. On the other hand, the available evidence of sex-specific differences in human milk composition are not well established [16][17][18][19][20][21].…”

Free Amino Acids in Human Milk: A Potential Role for Glutamine and Glutamate in the Protection Against Neonatal Allergies and Infections

“…Of the total content of amino acids (AAs) in human milk, 5-10% is present in free form. The FAAs glutamate and glutamine are by far the most abundant, both in absolute sense and relative to their protein-bound form, together comprising almost 70% of all FAAs present in human milk (35). Their levels display unique and consistent patterns over lactation, suggesting that secretion of these FAAs in human milk is a regulated process (35,36).…”

Glutamate Supply and Metabolism in Infants

“…Based on recently published longitudinal data on milk composition in European women [18], which we regard to be based on even better methodology, the estimated mean daily free Glu intake of a breastfed reference infant is 40 mg/kg bw and the intake at the upper end of the normal range is 70.2 mg/kg bw.…”

“…Recently, van Sadelhoff et al [18] published a methodologically impressive study on the longitudinal evolution of TAA and FAA contents in milk samples collected monthly from 1 to 6 months of lactation in the same group of European women, which provides important additional and presumably more precise information on the change of AA content with duration of lactation [18]. Again Glu was quantitatively clearly dominant among the FAA.…”