Breast-feeding protects girls from chest infections - but has no effect on boys

The team tracked a group of very low birth weight, pre-term infants to gauge the protective effect of breast-feeding against infections in babies.

They found that breast-fed girls were far less likely than breast-fed boys to develop serious respiratory infections requiring hospitalization.

Breast-fed babies also have fewer ear, stomach or intestinal infections

Bronchiolitis is an infection of the airways of the lungs seen most often in infants between three and six months old.

The researchers studied a group of 119 high-risk infants in Buenos Aires who weighed under 3.3 pounds at delivery. This population is highly susceptible to these kinds of infections.

Fifty per cent of the baby girls who were formula-fed had to be hospitalized when they experienced their first respiratory infection, compared to just seven per cent of breast-fed girls, the researchers wrote in the journal Pediatrics.

However, there was no difference between the boys who were breast-fed or formula-fed - with about 19 per cent of both groups needing hospitalization when they got their first respiratory infection.

The pattern repeated throughout the first year of life and in subsequent infections, the researchers said.

"There are many, many different diseases that are protected against by breast-feeding. It's a great source of nutrition. It's important for development. Everyone benefits from breast-feeding," Dr Fernando Polack of Johns Hopkins University in Maryland said.

"Now, in the specific case of acute respiratory diseases like bronchiolitis and viral infections of the respiratory tract, it seems that there is greater benefit in girls than in boys. And that benefit is substantial," he said.

Previous studies have found that breast-fed babies enjoy a range of health benefits compared to those given baby formula.

These include fewer ear, stomach or intestinal infections, digestive problems, skin diseases and allergies, and less risk of developing high blood pressure, diabetes and obesity. Some research has even suggested that breast-feeding can boost a baby's intelligence.

The NHS recommends a healthy mother to breastfeed her baby for the first six months.

For breastfeeding advice visit: http://www.breastfeeding.nhs.uk