Abstract
Human milk oligosaccharides (HMOs) are important functional biomolecules in human breast milk. Understanding the factors influencing differences in HMO composition and changes in their concentration over lactation can help to design feeding strategies that are well-adapted to infant’s needs. This review summarises the total and individual concentration of HMOs from data published from 1999 to 2019. Studies show that the HMO concentrations are highest in colostrum (average 9–22 g/L), followed by slightly lower concentrations in transitional milk (average 8–19 g/L), with a gradual decline in mature milk as lactation progresses, from 6–15 g/L in breast milk collected within one month of birth, to 4–6 g/L after 6 months. Significant differences in HMO composition have been described between countries. Different HMOs were shown to be predominant over the course of lactation, e.g., 3-fucosyllactose increased over lactation, whereas 2′-fucosyllactose decreased. Recent clinical studies on infant formula supplemented with 2′-fucosyllactose in combination with other oligosaccharides showed its limited beneficial effect on infant health.
Highlights
The concentration of human milk oligosaccharides (HMOs) in milk is higher than the amount of protein [1,2], highlighting their importance for the growing infant
While Human milk oligosaccharides (HMOs) chemical structure follows a basic blueprint, it has been reported that every woman synthesizes and secretes a distinct HMO profile and has a different individual HMO concentration profile that may be affected by maternal genetics [5], physiology [6], diet [7] and country of origin [8]
The variations observed between individuals in the same study are likely due to maternal factors such as Secretor and Lewis blood group status, which are not always taken into account or discussed in the reports. Other maternal factors such as country of origin, body mass index (BMI) and parity may play a role in HMO profiles, but their influence still needs to be demonstrated in extensive cohort studies
Summary
The concentration of human milk oligosaccharides (HMOs) in milk is higher than the amount of protein [1,2], highlighting their importance for the growing infant. While HMO chemical structure follows a basic blueprint, it has been reported that every woman synthesizes and secretes a distinct HMO profile and has a different individual HMO concentration profile that may be affected by maternal genetics (secretor status) [5], physiology [6], diet [7] and country of origin [8]. The effects of this distinct HMO composition on infant health outcomes have yet to be fully understood, a potential link between specific HMOs, milk microbiota and infant’s gut microbiota composition has been described [9–11].
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