London - Babies who are breastfed carry fewer potentially harmful viruses in their guts than infants given bottle milk, a study found.
At birth babies’ guts are a blank slate, with nearly no viruses present.
Scientists tested the stools of 20 babies aged up to four days. They then examined a group of 125 babies at between one and four months at a hospital in Philadelphia, US.
By four months just nine percent of babies given breast milk – or a combination of breast and bottle feeds – carried viruses. But 30 percent of infants fed only on formula milk had viruses at this age.
Viruses found included those that can cause stomach complaints.
The study suggests exclusive or partial breastfeeding protects babies. Infants can develop viral gastroenteritis, which results in diarrhoea and vomiting.
In the UK, rotavirus – a stomach bug which hits babies and young children – is the most common cause of gastroenteritis.
Acute gastroenteritis is a leading cause of infant death around the world, killing 600 000 to 875 000 babies and children each year. The study authors from the University of Pennsylvania, writing in Nature, said factors in breast milk likely to fight viruses include antibodies from the mother, sugars and proteins.
Dr Frederic Bushman, who led the research, said it was important to keep the number of viruses down in babies. He stressed: "Breastfeeding is valuable in supporting infant health. Our data and other work suggests that some breastfeeding is better than no breastfeeding."
Research has shown breastfed babies are less likely to be victims of sudden infant death syndrome, get leukaemia, become obese or suffer heart disease in adulthood.
Experts say breastfeeding also offers health benefits for mothers, including helping to reduce the risk of breast cancer.