By Amy Norton

NEW YORK (Reuters Health) - Children who attend daycare may have a lower risk of developing asthma later on, particularly if they start daycare between the ages of 6 and 12 months, a new study suggests.

The findings, published in the Journal of Allergy and Clinical Immunology, lend more support to the "hygiene hypothesis" -- the theory that the increasingly germ-free surroundings of modern life are actually contributing to an increase in allergies and asthma.

It's thought that exposure to the coughs and sneezes of daycare may affect the developing immune system in a way that makes allergic reactions less likely. Exposure to viruses and other bugs may help push a baby's immune system toward infection-fighting mode, and away from a tendency to over-react to the normally benign substances.

In the current study, researchers followed 1,085 children from birth to age 5. They found that those who attended daycare had a lower risk of wheezing by the time they were 5 years old, compared with children who stayed at home or with a babysitter.

The risk was particularly low among children who entered daycare when they were between the ages of 6 and 12 months. These children were 75 percent less likely than their peers who were cared for at home to develop a wheezing problem.

Similarly, children who went into daycare after the age of 12 months had a 35 percent lower risk of wheezing.

The findings suggest that the timing of a child's entrance into daycare -- and, therefore, exposure to viruses and bacteria -- may play an important role in the maturation of the immune system, lead researcher Dr. Nicolaos C. Nicolaou told Reuters Health.

However, the study does not prove that this is the case, added Nicolaou, of the University of Manchester in the UK.

"Indeed, we do not know for certain what within the daycare environment might be affording this observed protection," said Nicolaou. "This is only one piece in the jigsaw puzzle."

Nor do the findings suggest that parents should choose daycare for the sake of their children's health, the researcher noted.

"Daycare attendance has other benefits and disadvantages," Nicolaou said, "and parents need to weigh up the pros and cons of daycare for their individual child and family."

More research is also needed to see whether only certain children gain asthma protection from attending daycare, according to Nicolaou. Genetic susceptibility to allergies and asthma, for example, is likely to be important.

SOURCE: Journal of Allergy and Clinical Immunology, August 23, 2008.

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