New research reveals the remarkable complexity of human milk

Two major international studies are providing new insight into how human milk is regulated, showing  that some components respond to maternal nutrition, while others remain stable or reflect biological processes involved in lactation and infant growth.

Published Oct. 8 in Science, the studies were conducted by the International Milk Composition (IMiC) Consortium, a global collaboration led by the University of Manitoba involving more than 20 researchers from 13 organizations across six countries and four continents.

Funded by the Gates Foundation, IMiC was created to study human milk as a complex biological system rather than as a simple collection of nutrients. One study looked at maternal nutritional supplement during lactation and how it can modify important parts of breast milk. The second study discovered that milk could offer clues about how the lactating breast is functioning and how this relates to infant growth.

“Together, the studies show that human milk is neither completely fixed nor simply a reflection of maternal diet,” said Dr. Meghan Azad, IMiC director, UM Canada Research Chair in early nutrition and the developmental origins of health and disease, and a professor of pediatrics and child health at the Max Rady College of Medicine, Rady Faculty of Health Sciences. “Some components respond readily to maternal nutritional interventions, while others are tightly regulated or reflect the biology of the lactating breast.”

Azad, also a research scientist with Children’s Hospital Research Institute of Manitoba, said this was one of the largest and most comprehensive efforts to study the complexity of human milk across diverse populations. More than 1,000 mother and infant pairs from Canada, Burkina Faso, Tanzania and Pakistan took part in the studies. The mothers contributed nearly 2,000 human milk samples, which were analyzed for more than 25,000 compounds.

How maternal nutrition changes human milk

The first study found that some components of human milk respond clearly to maternal nutritional supplementation, including B vitamins, selenium and triglyceride profiles, while others do not change.

“This tells us that milk is not simply a reflection of what a mother eats, but a highly regulated biological system,” said Dr. Trenton Dailey-Chwalibóg, lead author and senior research fellow at Ghent University’s Faculty of Bioscience Engineering, and principal investigator at Agence de Formation, de Recherche & d’Expertise en Santé pour l’Afrique (AFRICSanté) in Burkina Faso. “At the same time, identifying which milk components are modifiable opens the door to designing maternal nutritional supplements more deliberately, with the goal of optimizing what is delivered to the infant through milk.”

The study results show that nutritional supplementation after birth may improve the micronutrient content of milk received by breastfed infants, especially in settings where maternal undernutrition is common.

Human milk offers a window into mammary gland function and infant growth

The second study identified shared patterns in human milk linked to distinct aspects of mammary gland function encompassing milk synthesis and secretion, epithelial barrier and tissue remodeling, and immune and repair activity. The results demonstrate the value of examining milk in the context of mammary gland biology to better understand the links between maternal metabolism and infant growth.

“Human milk gives us a rare, non-invasive window into the biology of the lactating mammary gland,” said Dr. Liat Shenhav, the mammary gland study senior author and an assistant professor at New York University’s Grossman School of Medicine. “By looking at molecular patterns across diverse populations, we can begin to identify shared features of mammary function and understand how they relate to maternal metabolism and infant growth.” 

The study results open new directions for understanding lactation biology and designing future interventions to support maternal nutrition, mammary function and infant growth.