New mothers have long been told that breast milk is best for their baby, and now there's more evidence that breastfeeding helps protect babies against potentially harmful viruses.
With the coronavirus pandemic on everyone's mind, the new research is especially timely. However, the report did not look specifically at the virus that causes Covid-19.
For the study, the investigators analysed the types and numbers of viruses in the first and subsequent stools of hundreds of newborns in the United States and Botswana.
Immediately after birth, the babies had little or no evidence of viruses or bacteria, but their numbers were high by time the babies were a month old, the researchers found.
Mothers encouraged to breastfeed
Most of the first wave of viruses were beneficial ones, but those that can make people sick were more prominent by age four months. However, breastfeeding suppressed the accumulation of potentially dangerous viruses among babies in both countries.
The University of Pennsylvania researchers also concluded that breast milk mixed with formula still offers more protection against harmful viruses than formula alone, according to the study published on 15 April in the journal Nature.
"These findings can help us better understand why some babies get sick and develop life-threatening infections in their first months of life," said study senior author Frederic Bushman, chair of the department of microbiology at UPenn.
The study adds to previous research suggesting that breastfeeding plays an important role in the interaction between infants and microbes, and could help guide strategies to prevent early gastrointestinal disorders and encourage mothers to breastfeed their babies, even if they mix breast milk with formula, the authors said.
Location plays a role
The study also found that babies in Botswana were more likely to have potentially harmful viruses in their stools at four months of age than babies in the United States.
"Location of the mom and baby seems to play a role, probably due to the kind and number of microorganisms babies are exposed to environmentally," study first author Guanxiang Liang, a postdoctoral researcher in the department at microbiology, said in a university news release.
"Nevertheless, Botswana-born babies still seemed to benefit from breastfeeding, whether exclusively or in addition to formula consumption," Liang added.