Study finds breastfed girls protected from chest illness

Breastfeeding protects baby girls from serious chest infections, but does little to prevent respiratory illnesses in boys, researchers have found.

Doctors monitored 119 premature babies through their first year of life and found that girls who received formula were eight times more likely to be hospitalised with respiratory illnesses than those weaned off breast milk.

But breastfeeding did not have the same protective effect on boys. Nearly a fifth of boys developed respiratory infections severe enough to need hospital treatment, whether they were breastfed or not.

The study is the first to show gender differences in the health benefits of breastfeeding and overturns the previously held belief that breast milk contains protective chemicals from the mother's immune system that pass directly to her baby. Were that the case, both boys and girls would benefit equally, the researchers write in the journal Pediatrics.

Dr Fernando Polack, an infectious disease specialist at Johns Hopkins children's centre in Baltimore, said breastfeeding did not affect the number of infections baby girls caught, but reduced their severity, meaning breast milk helped them to cope with infections better.

"We are starting to think that milk does not directly transfer protection against lung infections but instead switches on a universal protective mechanism, already in the baby, that is for some reason easier to turn on in girls than in boys," said Polack.

In the study, the team investigated how babies fared after picking up their first respiratory infection. Only 6% of breastfed girls were hospitalised by their chest infection, compared with half of the girls who were weaned off formula. There was almost no difference between boys, with 18% breastfed and formula-fed boys hospitalised by their first chest infection.

The protective benefit of breastfeeding remained the same as babies picked up more infections throughout their first 12 months of life.

The findings are particularly relevant to families in developing countries where antibiotics and other drugs may be scarce and where an estimated quarter of premature babies are hospitalised with serious chest infections.

"When resources are limited, it helps to know that your high risk group is formula-fed girls," said Polack.

The findings, he said, suggested that mothers of premature girls should be strongly urged to breastfeed their infants.

If breast milk can trigger a protective mechanism against respiratory infections, the next puzzle will be to understand why it is more easily activated in girls than boys. If scientists can unravel the mystery, it could lead to treatments that mimic the effect.

Last month, a Canadian team published the most comprehensive study conducted, and found that exclusively breastfed children scored up to 7.5 points higher in intelligence tests.

FAQ Breastfeeding

Should women still breastfeed baby boys? Yes. The latest study found that breastfeeding did not protect boys from serious chest infections, but it does seem to have other benefits.

What are the benefits of breastfeeding? Studies show that children who are breastfed are healthier than those fed on formula. Breastfeeding seems to boost intelligence slightly and has been linked to lower rates of obesity.

Where does the research lead? If scientists can pin down how breast milk boosts babies' immune systems, they may be able to develop drugs that mimic the effect and that could help protect baby boys from infection.

· This article was amended on Tuesday June 3 2008. Babies are weaned off breast milk, rather than on it as we said in the article above. This has been corrected.

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