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Human milk composition provides the standard for human infant nutrition, including the bioactive components that safeguard infant growth and development.
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The composition of human milk is variable within feeds, diurnally, over lactation, and between mothers and populations. This variability has benefits for infant health and survival, but for high-risk infants requiring close nutritional oversight, strategies for managing the variability of human milk feeds are needed.
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The composition of human
Human Milk Composition: Nutrients and Bioactive Factors
Section snippets
Key points
Stages of lactation
The first fluid produced by mothers after delivery is colostrum, which is distinct in volume, appearance, and composition. Colostrum, produced in low quantities in the first few days postpartum, is rich in immunologic components such as secretory immunoglobulin (Ig)A, lactoferrin, leukocytes, and developmental factors such as epidermal growth factor (EGF).4, 5, 6 Colostrum also contains relatively low concentrations of lactose, indicating its primary functions to be immunologic and trophic
Studies of human milk composition
A Medline search using only the phrase “human milk composition” reveals a steady increase in publications since the 1960s, with new components still being identified in human milk and the functionality of those components under active investigation in many laboratories worldwide. Many studies of human milk composition have been conducted in diverse populations using varied collection, storage, and testing methods. The gold standard of milk collection involves sampling of all milk expressed over
Nutritional components of human milk
The nutritional components of human milk derive from 3 sources: some of the nutrients of milk originate by synthesis in the lactocyte, some are dietary in origin, and some originate from maternal stores. Overall the nutritional quality of human milk is highly conserved, but attention to maternal diet is important for some vitamins and the fatty acid composition of human milk (see article elsewhere in this issue by Valentine and Wagner).
Bioactive components and their sources
Bioactive components of food are defined as elements that “affect biological processes or substrates and hence have an impact on body function or condition and ultimately health.”32 Bioactive components in human milk come from a variety of sources; some are produced and secreted by the mammary epithelium, some are produced by cells carried within the milk,33 whereas others are drawn from maternal serum and carried across the mammary epithelium by receptor-mediated transport. Furthermore, the
Growth factors
Human milk contains numerous growth factors that have wide-ranging effects on the intestinal tract, vasculature, nervous system, and endocrine system.
Immunologic factors
Feeding human milk protects against infection and inflammation,86 and early milk is enriched in immune factors that help to ensure infant survival.15 The specific protective components of human milk are so numerous and multifunctional that science is just beginning to understand their functions.
Impact of storage and pasteurization on milk components
Increasingly, human milk feeding occurs apart from feeding at the mother’s breast. Most lactating women in North America now express and store their milk at some time.156 Varying degrees of nutrient loss occurs, depending on the nutrient and the storage methods. For vitamin C loss occurs rapidly, even during the process of feeding freshly expressed human milk by bottle.155 For multiple human milk components, however, significant degradation may occur only with long-term storage and freeze-thaw
Management or Augmentation of Human Milk Factors
Recognition of the dynamic variability of human milk is important to the management of human milk feeding. For example, mothers of term infants are commonly advised to empty an entire breast before feeding from the other breast. As hindmilk is more energy dense because of its higher lipid content, this recommendation ensures that infant satiety and energy needs for growth are well met. Hindmilk has been successfully used to improve growth of very premature infants, and is recommended for their
Summary
Human milk is a dynamic, multifaceted fluid containing nutrients and bioactive factors needed for infant health and development. Its composition varies by stage of lactation and between term and preterm infants. While many studies of human milk composition have been conducted, components of human milk are still being identified. Standardized, multipopulation studies of human milk composition are sorely needed to create a rigorous, comprehensive reference inclusive of nutrients and bioactive
Acknowledgments
The authors gratefully acknowledge Donna Wuest for assistance with manuscript preparation.
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Cited by (0)
Disclosures: Dr Morrow has grant funding from Mead Johnson Nutrition, Inc. to study the composition of human milk. This work was supported in part by grants to Dr Morrow from the National Institute of Child Health and Human Development (P01 HD 13021 “The role of human milk in infant nutrition and health”) to study bioactive factors in human milk and from Mead Johnson Nutrition, Inc to conduct a comprehensive study of human milk factors (“The Global Exploration of Human Milk [GEHM] Study”).