Human milk is usually discussed as food for the baby. A new study in Science treats it as something else as well: a readout of the organ that makes it. By analysing thousands of molecular measurements in milk from mothers in three very different settings, researchers at NYU Grossman School of Medicine found shared patterns that connect what a mother’s body has available, how her mammary gland is working, and how her infant grows.

The problem: milk studied one molecule at a time

Milk contains thousands of nutrients, metabolites, proteins, immune factors and other molecules. Research has often looked at these one by one, which makes it hard to see the gland that produces them. Senior author Liat Shenhav describes milk as “a rare, non-invasive window” into the biology of the lactating mammary gland, and it can be collected repeatedly over time.

What the team did

The researchers analysed 1,543 milk samples from three cohorts in Canada, Pakistan and Burkina Faso. They combined several molecular layers (metabolites, proteins, vitamins and other micronutrients, macronutrients such as carbohydrates, and human milk oligosaccharides) with infant growth data, and used machine learning to find patterns. Two of the cohorts came from randomized nutritional trials in which maternal supplementation helped infants at higher risk of poor growth recover or stay stable.

They also mapped the milk patterns onto three aspects of how the mammary gland works:

  • milk synthesis and secretion, meaning how mammary cells make milk components and release them;
  • epithelial barrier and tissue remodelling, meaning what passes between blood and milk, and how the milk-producing tissue is reshaped;
  • immune and repair activity, meaning how the gland protects itself and recovers from stress or injury.

Seven candidate biomarkers

One pattern of milk composition was linked both to maternal supplementation and to infant growth. Digging into which molecules drove it, the team identified seven candidate biomarkers associated with maternal nutritional status, infant growth and mammary gland biology: four short-chain acylcarnitines (C2, C3, C4 and C5), the amino acid lysine, the milk sugar 6′-sialyllactose, and the mineral selenium. Together they captured aspects of mammary biology beyond established measures of blood-milk barrier permeability.

The short-chain acylcarnitines, which help cells process nutrients for energy, showed the strongest links, with C5 the most prominent signal. Higher C5 was associated with weaker milk-synthesis signatures and with patterns related to tissue remodelling and immune activity.

A proposed link to vitamin B5

Acylcarnitine metabolism depends on coenzyme A (CoA), a central molecule in energy and fat metabolism that the body makes from pantothenic acid, also known as vitamin B5. Drawing on associations across the cohorts and established biochemistry, the authors propose that low vitamin B5 availability could limit CoA-dependent metabolism and contribute to altered acylcarnitine profiles, including a build-up of C5. They call this a plausible route and say they are now testing it.

A companion paper

The study is one of two papers in Science from the International Milk Composition (IMiC) Consortium, which profiled more than 25,000 molecular features in milk from over 1,000 mother-infant pairs. The companion paper asked which milk components can actually be changed through maternal nutrition. Its finding, as summarised in the press release, is that supplementation during lactation raised several B vitamins in milk, while many other components stayed comparatively stable. Milk, in other words, is neither fixed nor a simple mirror of what a mother eats.

What to keep in mind

  • These are associations. The study identifies patterns that travel together, not proven causes.
  • The seven markers are candidates. Nothing in the release suggests they are ready for clinical use.
  • The vitamin B5 explanation is a hypothesis the authors are still testing, not an established mechanism.
  • This is not advice about supplements. Questions about nutrition during pregnancy or breastfeeding are best taken to a doctor, midwife or dietitian.
  • This post is based on the institutional press release and its summary of the paper. I have not been able to read the full paper, so figures and details are as the release reports them.

What makes the work interesting is the shift in framing. If milk reliably reflects how the mammary gland is functioning, it could become an easy, repeatable way to study the interface between a mother’s nutrition and her baby’s growth. The team is now looking at colostrum and transitional milk to see how mammary function emerges after birth.

Sources