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Breast milk contains millions of cells. What are these cells and what do they reveal?
Human mammary glands can produce more than a litre of breast milk a day, but studying how mammary glands actually produce the milk is tricky. Now a new large-scale, high-resolution study provides some fascinating insights into milk production through analysis of the cells contained in breast milk. The study reveals milk-producing cells change over time in breastfeeding mothers.

Breast milk is a dynamic fluid that is incredibly complex.
Amazing breast milk fact #1
Human mammary glands can produce more than a litre of milk a day, and this can continue for years after birth.
Amazing breast milk fact #2
Amongst a long list of complex components, human milk contains millions of cells.
Many of these cells relate to milk production.
These cells are thought to enter the milk through the process of breastfeeding.
Studying mammary gland cells in mothers is tricky as the tissue can’t be biopsied, and can’t be accessed during breastfeeding.
So by analysing the cells found in breast milk, this provides a non-invasive way to study lactational cells.
So what are the cells in human milk that reveal the dynamics of human milk production, and how do a mother’s milk-producing cells change over time?
A new large-scale, high-resolution study including researchers from MIT provides some answers.
This blog article is (hopefully) an easy-to-understand explanation of some of the key points from this new study.
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The Study:
Researchers looked at the cells in human milk produced by 15 donors.
Each donor provided breast milk samples at multiple time points; from three days after birth to nearly two years postpartum.
In total, 48,000 cells from 50 samples were analysed using single-cell RNA-sequencing (scRNA-seq). This type of…