by Three parts Advances in Nutrition A systematic review finds that there is much we still do not know
The World Health Organization (WHO) recommends exclusive breastfeeding for the first six months and continued breastfeeding as part of an infant’s diet up to at least two years of age. The favorable growth and development outcomes observed in infants breastfed according to WHO guidelines can be attributed to the array of nutritional and non-nutritive components of human milk. On the other hand, suboptimal breastfeeding may result in up to 1.4 million child deaths, particularly in the first six months of life, and may account for an estimated 10% of the total burden of childhood disease all over the world.
Despite a significant increase in human milk research in recent years, there are still large gaps in our understanding of how the components of human milk affect the growth and development of children. However, as technology improves, there is increasing pressure to expand the breadth and scope of current research, moving beyond single nutrient analysis to explore the various components of human milk and their Combined clinical outcomes in children.
“Human Milk Composition and Child Growth and Body Composition in the First 2 Years: A Systematic Review,” published in Advances in Nutrition, explores the current evidence to help us better understand the link between human milk components and growth and body composition during the first two years of life. Due to the large number of research studies in this field, the results were organized in three manuscripts dedicated to (1) human milk macronutrients, (2) human milk micronutrients, and (3) biologically active (bioactive) human milk components.
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The authors involved in this three-part review are part of the International Milk Composition Consortium funded by the Bill & Melinda Gates Foundation and led by Dr. Meghan Azad, Level 2 Canada Research Chair in Early Nutrition and the Developmental Basis of Health and Disease. The International Milk Composition Consortium was established in 2020 to bring together maternal-child health and human milk researchers and statistical experts to develop an efficient, harmonized approach to human milk research and analysis. Among the authors are Dr. Meredith Brockway and ASN members Lindsay H. Allen, Daniela Hampel, and Sarah M. Reyes.
Below is a brief summary of the main findings from each of the three manuscripts:
Human Milk Nutrition Macros and Child Growth and Body Composition in the First 2 Years: A Systematic Review
Micronutrients in human milk have been well studied. However, their relationship to growth and body composition in early life is still not well understood. In response, the authors of this review conducted a systematic search of the scientific literature, which yielded 57 studies that explored the relationship between human milk macronutrients and infant growth and body composition collected from 5,979 mother-infant litters. Overall, the authors found that “digestible carbohydrates were positively associated with infant weight outcomes.” Additionally, “protein was positively associated with infant length, but no associations were reported for infant weight.” Interestingly, “human fat was not consistently associated with any infant growth metric.” The authors noted that their ability to draw strong conclusions was limited by differences in study design as well as inadequate reporting of results. Going forward, the authors urge researchers to “accurately record and account for exclusive breastfeeding; 648/2012 Text relevant to the EEA to use consistent sampling protocols that account for the temporal variation in human milk macronutrients; and use reliable, sensitive and accurate techniques for macronutrient analysis of human milk.”
Human Milk Micronutrients and Child Growth and Body Composition in the First 2 Years: A Systematic Review
Micronutrients play a vital role in the growth and development of children. Although it is well documented that deficiency in some micronutrients, such as zinc, iron, and vitamin A, can lead to poor childhood growth, knowledge of the specific relationships between human milk micronutrients and infant and child growth is incomplete. In particular, “this systematic review reveals that little is known about how individual human milk micronutrients influence the anthropometry of infants and young children.” The authors noted that data were scarce for many micronutrients. Moreover, despite the WHO recommendation of breastfeeding for at least two years or longer, most of the studies focused on the first six months of life. However, the authors noted that “current evidence suggests a positive correlation between infant growth and human milk concentrations of iodine, manganese, calcium and zinc.” However, the authors cautioned that even these relationships are “largely unclear due to sparse data, small sample sizes, and methodological limitations of existing studies.”
Human Milk Bioactive Components and Infant Growth and Body Composition in the First 2 Years: A Systematic Review
Human milk non-nutritive bioactivators, including hormones, human milk oligosaccharides and immunomodulatory components, can have long-lasting effects on the infant microbiome, immune function, and growth and development. Although infant formula can deliver the nutrients found in human milk, it does not replace many of the vital non-nutrient bioactives of human milk. The largest body of evidence among these bioactive components of human milk shows an inverse relationship between the concentrations of the hormones leptin and adiponectin with infant growth, although not all studies were in agreement. Overall, however, this systematic review showed “inconsistent associations between bioactive components of human milk and infant body composition in the first two years.” In addition, it “highlighted inconsistent data collection methods and identified many knowledge gaps for future research.” The authors believe that “future research should ideally capture human milk intake, use biologically relevant anthropometry, and integrate components across categories, adopting a systems biology approach to better understand to discover how the components of human milk work independently and synergistically to influence infant growth.”
We invite you to explore this three-part systematic review in its entirety to gain a deeper understanding of the relationship between human milk components and childhood growth and development. In addition, the authors can point you to areas where more research is needed to improve the health of infants and children.
