Babies are helped to fight infections by the composition of breast milk, say researchers in Greece.
World experts already recommend that infants are exclusively breastfed for at least the first six months of life.
For the study, the researchers tracked the health of 926 infants for a period of 12 months, recording any common infections these babies had during their first year of life.
All the newborns were routinely vaccinated and had access to a high standard of healthcare.
Overall, 91 of the infants were exclusively breastfed for a full six months.
Subsequently, these infants had significantly fewer common infections during their first year of life than their peers who were either partially breastfed or not breastfed at all.
These included respiratory and ear infections, as well as thrush.
Professor Emmanouil Galanakis and his team say it is the composition of breast milk that explains their findings, reports the BBC.
Breast milk contains antibodies passed from the mother, as well as other immunological and nutritional factors that help the baby fight off infections.
The study is published in Archives of Diseases in Childhood.