Breast Milk Contributes Significantly to Babies' Bacteria

The importance of delivery method for the development of babies’ gut bacteria has come into question in recent months. A new study from University of California, Los Angeles, reports how another aspect of newborn life influences the nascent gut microbiome: breastfeeding. The study, published Monday (May 8) in JAMA Pediatrics, found that 30 percent of babies’ gut bacteria seem to come from the mother’s breast milk and that another 10 percent can be traced to skin around the mother’s nipple.

“Breast milk is this amazing liquid that, through millions of years of evolution, has evolved to make babies healthy, particularly their immune systems,” UCLA’s Grace Aldrovandi, the study’s lead author, said in a press release. “Our research identifies a new mechanism that contributes to building stronger, healthier babies.”

In 107 mother-infant pairs, the study examined the microbial content of the mother’s milk, the skin around the mother’s nipple, and the baby’s stool, whose bacteria represent those of the gut. As Reuters reported, the bacteria in infants’ poop were more similar to the microbes from their own mothers than those from other mothers in the study, suggesting that the bacteria are transferred from mother to child through breastfeeding.

This study did not examine baby health. However, previous research indicates that breastfeeding wards against obesity and aids immune-system development. Doctors recommend exclusive breastfeeding for the first six months because it is associated with a reduced risk of ear and respiratory infections, allergies, diabetes, and sudden infant death syndrome, Reuters noted.

“We’ve always assumed that most of these microbes come from the mother,” University of Minnesota gastroenterologist Alexander Khoruts told Reuters. “They found that breastfeeding is the major source of microbial transfer during the early months of life, and I think the study provides supportive evidence for the current recommendations of exclusive breastfeeding for the first six months and continued breastfeeding to 12 months.”