Infographic: The Biology of Human Milk (Text Alternative)

Human milk is a complex biological system with many components and functions. Despite its importance, there is still a lot we don’t know about it. A deeper understanding of human milk biology is essential for addressing ongoing and emerging questions about infant feeding practices.

Factors that influence human milk production include:

  1. Mammary gland development;
  2. Maternal factors including diet, health, genetics, stress, and the environment
  3. Infant factors such as size, health, sex, and gestational age. Importantly, both maternal and infant factors affect human milk volume, composition, and energy density.

The composition of human milk includes macronutrients, micronutrients, bioactives, and the milk microbiome. Bioactives include immunoglobulins, hormones, proteins, human milk oligosaccharides, white blood cells, peptides, cytokines and chemokines, and microRNA.

Advances in technology for human milk analysis can enhance our understanding of the components of human milk and their function as well as the impact that chronobiology, including the stage of lactation, the time of day, and the time between feeds, has on the composition and function of human milk.

As we study the components of human milk, their functions, and their mechanisms of action, we can determine how they affect maternal health, the health and nutritional status of the infant, and child health issues such as growth and body composition, micronutrient status, gut health, neurodevelopment, and immune development.

Why it Matters

  • A deeper understanding of the biology of human milk is essential to address ongoing and emerging questions about infant feeding practices.
  • NICHD’s research will have important implications for global policy, nutritional guidance, and interventions.

What Do We Know?

  • Human milk is a complex biological system that is more than the sum of its parts.
  • Human milk production should be studied as an interactive system consisting of inputs from the lactating parent, their breastfed baby, and their respective environments.

What Questions Remain?

Thanks to the last 20 years of human milk research, we are entering the next level of scientific questions about human milk.

  • How do the qualities of the lactating parent affect milk composition?
  • What are the components of human milk and how do they interact with each other in this complex biological system?
  • How does the infant affect milk composition and production?
  • How can new technologies and methodologies be applied to study human milk as a complex biological system?
  • How can new human milk research be translated and implemented to support safe and effective feeding practices?

To answer these questions, NICHD launched the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project.

Calls to Action


Parul Christian, Emily R Smith, Sun Eun Lee, Ashley J Vargas, Andrew A Bremer, Daniel J Raiten, The need to study human milk as a biological system, The American Journal of Clinical Nutrition, Volume 113, Issue 5, May 2021, Pages 1063–1072, external link

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