Health · Medical Research · 8 hrs ago
Study suggests breast milk urea may influence infant gut bacteria
Researchers found that urea levels in breast milk change during lactation and may affect the bacteria developing in an infant’s gut.
Urea is usually known as a waste product, but the study suggests it could also play a role in shaping the infant gut microbiome.
In lab tests, a strain of Bifidobacterium longum grew best at levels typical of early lactation, while higher levels supported Klebsiella pneumoniae.
Five of the eight formulas tested had more urea than human milk, and formula levels do not change with lactation in the same way.
The researchers also found genes linked to urea metabolism in samples from milk and infant stool, but the study does not prove urea changes babies’ health.
The findings come from a preliminary study that has not been peer-reviewed, so they are not established guidance for feeding or health.
A non-peer-reviewed study suggests that urea in breast milk could influence the developing infant gut microbiome.
Researchers found that milk urea levels change during lactation and that tested infant formulas did not show the same changing pattern.
Five of the eight formulas tested contained higher urea concentrations than human milk.
In laboratory tests, different urea concentrations favored different bacteria.
The study combined human cohorts, a mouse model and microbiome analyses.
- Who
- Researchers from universities and institutions in the United States and other countries.
- What
- The study examined breast milk urea, how its levels change, and its potential effects on infant gut bacteria.
- When
- Published as a preprint on bioRxiv; News-Medical published its report on 2026-11-10.
- Where
- The research included cohorts in North America and South Africa, as well as a mouse model.
- Why
- To investigate how breast milk urea is regulated during lactation and whether it may affect the developing infant gut microbiome.
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- North American cohort
- 38 mothers
- New Jersey Kids Study
- 63 mother-infant pairs sampled between weeks 4 and 20 postpartum
- South African cohort
- 23 mothers nursing four-week-old infants
- Formula comparison
- Five of eight tested products had higher urea concentrations than human milk
- Study status
- BioRxiv preprint; not peer-reviewed