By Will Dunham

WASHINGTON, June 2 (Reuters) - Breast-feeding gives all infants numerous health advantages compared to baby formula, but in at least one respect girls get a greater benefit from breast milk than boys, researchers said on Monday.

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

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

A lot of research has shown that breast-fed babies enjoy a range of health benefits compared to those given baby formula beyond combating respiratory infections.

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. And some research has shown breast-fed babies are smarter, too.

"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 Baltimore, Maryland, one of the researchers, said in a telephone interview.

"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.

Bronchiolitis is an infection of the airways of the lungs seen most often in infants between about 3 and 6 months old.

The researchers studied a group of 119 high-risk infants who weighed under about 3.3 pounds (1,500 grams) at delivery. This population is highly susceptible to these kinds of infections, Polack said.

Fifty percent of the baby girls who were formula-fed had to be hospitalized when they experienced their first respiratory infection, compared to about 7 percent of the girls who were breast-fed, the researchers wrote in the journal Pediatrics.

There was no difference between the boys who were breast-fed or formula-fed -- with about 19 percent of both groups needing hospitalization when they got their first respiratory infection, the researchers said.

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

Polack said there may be something in the breast milk that better activates a baby girl's ability to cope with such infections more so than it does for a baby boy.

The American Academy of Pediatrics recommends that women who do not have health problems exclusively breast-feed their infants for at least the first six months, with it continuing at least through the first year as other foods are introduced.

(Editing by Eric Beech)

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