Study finds breastfeeding routines have little effect on breast milk bacteria makeup.
New research on breast milk bacteria is changing what people thought they knew about how breastfeeding works. Scientists once assumed that how long and how often a mother breastfeeds could shape the mix of bacteria in her milk. But after looking closely at samples from hundreds of women, researchers now say that might not be the case at all. The bacteria found in breast milk seem to stay pretty steady, no matter how often babies feed or how much milk is produced. This surprises many people who assumed more time at the breast would naturally mean more bacteria passed between mother and baby.
The study, part of a project called BLOSOM, looked at milk samples from mothers about three months after they had given birth. Samples were taken from only one breast per person. Most of the women in the group were white and already had children, which may matter when thinking about how widely these results apply to everyone. Each milk sample had many kinds of bacteria, mostly ones you’d also find on the skin or in the mouth. These included types like Streptococcus mitis, Streptococcus salivarius, and Cutibacterium acnes. These three types made up the majority of the bacteria found in the samples.
Researchers checked to see if there was any connection between breastfeeding practices and the types of bacteria in the milk. They looked at how many times a day women breastfed, how long they fed overall in 24 hours, and how much milk was being removed. For the most part, these things didn’t seem to matter. The only small connection they found was between the length of daily breastfeeding and the amount of S. salivarius, a common mouth bacterium in babies. This may suggest that when babies nurse longer, more of their mouth bacteria flow back into the breast, where it ends up in the milk. But this was a weak connection, and other types of bacteria didn’t seem to follow the same pattern.
In short, the study showed that the mix of bacteria in milk doesn’t change much with different feeding styles. Other things may matter more. These could include how a mother expresses milk (by hand or pump), how often she washes her hands or cleans her pump parts, and whether anyone else feeds the baby using pumped milk. Some other studies have found bacteria in milk even before breastfeeding starts, which suggests that some bacteria are already present in the breast before the baby is even born.
One thing that stood out was how feeding frequency did not match up with the amount of milk taken in 24 hours. This goes against what many people might expect. You’d think that more feeding time means more milk, but that wasn’t the case here. Also, even though some bacteria might grow over time with more nursing, this might not show up clearly in the data if researchers are only looking at how much of each type there is compared to others. That’s because when one kind of bacteria grows a lot, it can make others seem smaller in comparison, even if they didn’t change at all in number.
The researchers say we need more studies that include people from different backgrounds and include both breasts in the sampling. They also suggest using better testing methods that can count exact numbers, not just percentages. For now, though, it looks like breastfeeding style doesn’t do much to change what bacteria end up in milk. That may be reassuring for mothers who worry about having to follow a perfect routine. No matter how often or how long they feed, their milk still carries the bacteria their baby likely needs.
Sources:
Breastfeeding habits barely change milk’s microbiome, study reveals
The human milk microbiome is minimally associated with breastfeeding practices
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