Breastmilk helps fight infections in babies and their mothers, international research led by the University of Western Australia has revealed.
Scientists say their findings help to explain why babies who are exclusively breastfed have fewer infections than babies who are fed formula.
The research team from UWA and University Freiburg in Germany recruited 21 breastfeeding mothers and their babies at different stages of lactation, ranging from a few days after birth to years into lactation.
They found that the leukocytes, or immune cells, in breastmilk increased rapidly when the mother or baby had an infection, and returned to normal when the infection was over.
It was the same when only the baby had an infection and the mother was asymptomatic, reinforcing the importance of breastfeeding for the protection of the baby, researchers said.
"In places where families don't have ready access to medicine, particularly developing countries, breastfeeding may be a determining factor in infant recovery and survival," the study authors said.
"Formula doesn't offer this protection and the ability to adjust to infant needs."
The researchers said their findings presented new information relevant to updating public policy on infant nutrition to maximise immunological protection.
"At the same time, they offer new grounds for examining the mechanisms behind the very low rates of symptomatic HIV and cytomegalovirus disease in infants exclusively breastfed by infected mothers," they said.
Findings also suggested babies who were not exclusively breastfed received not only lower breastmilk volumes, but also breastmilk that contained fewer leukocytes.