Nucleotides: an updated review of their concentration in breast milk

Our knowledge about the complexity of human milk, in particular fatty acid, protein, and oligosaccharide profiles, has increased considerably in recent years. However, little atten-tion has been paid to nucleotides, which account for-2% to 5% of the nonprotein ni-trogen fraction of breast milk and provide important cellular and metabolism functions for the infant. We examined literature published in the past 25 years to provide an up-dated review of concentrations of nucleotides in breast milk across lactational stages in mothers around the world. The free mononucleotides found in highest concentrations in breast milk are, from highest to lowest in the order of cytidine 5'-monophosphate, uri-dine 5'-monophosphate, and adenosine 5'-monophosphate, guanosine 5'-monophosphate, and inosine 5'-monophosphate. Levels of nucleotides varied considerably amongst indi-vidual mothers and with stage of lactation. They could be further influenced by time of day and season and the mother's diet. Levels of free nucleotides varied between studies undertaken in different regions; however, in studies that measured total potentially avail-able nucleotides levels, regional differences were not apparent. Some studies report higher amounts in colostrum and transition milk compared with mature milk, whereas other stud-ies report the converse. Recently, clinical studies showed that there are benefits to supple-ment nucleotides in infant formula. Although comparing data in the literature remains a challenge because of different milk collection methodologies and measurement protocols used by different studies, the information may provide insights for designing of formula products for infant at different stages of development. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

Our understanding of nucleotides in human milk has been limited compared to other components such as fatty acids, proteins, and oligosaccharides. This review examines literature from the past 25 years to provide an updated overview of nucleotide concentrations in breast milk across lactational stages and regions. The levels of nucleotides in breast milk vary greatly among individual mothers, lactation stages, and potentially influenced by factors like time of day, season, and diet. While levels of free nucleotides differ between studies conducted in different regions, total potentially available nucleotides show no apparent regional differences. Recent clinical studies suggest benefits of nucleotide supplementation in infant formula. The information from this review may contribute to the development of formula products for infants at different stages of development.