Another study backs up the belief that "breast is best" when it comes to a baby's health.
In the report, Finnish researchers say that breastfeeding appears to protect babies from dangerous antibiotic-resistant bacteria.
Due to their weak immune systems, more than 200 000 newborns worldwide die each year of infections caused by antibiotic-resistant bacteria, the study authors said.
But the researchers found that infants who were breastfed for at least six months had a smaller number of resistant bacteria in their digestive tract than babies breastfed for a shorter length of time or not at all.
The University of Helsinki researchers also found that infants of mothers who received antibiotics during delivery had higher levels of antibiotic-resistant bacteria in their gut. This effect was still present six months after birth.
"We cannot advise that mothers should not be given antibiotics during delivery," study author Katariina Parnanen said in a university news release.
"The consequences of infection for both mother and infant are potentially serious. What we can state is our findings, and physicians can use them to consider whether practices should be changed or not," the microbiologist said.
A third study finding was that breast milk also contains antibiotic-resistant bacteria, and that a mother is likely to pass these bacteria on to the child through breast milk.
But breastfeeding still reduces the number of resistant bacteria in the infant gut, the researchers reported.
"The positive effect of breastfeeding was identifiable also in infants who were given formula in addition to breast milk. Partial breastfeeding already seemed to reduce the quantity of bacteria resistant to antibiotics," Parnanen said.
The findings were published online recently in the journal Nature Communications.