Day Care May Cut Allergy
Risk, Raise Asthma Risk

NEW YORK (Reuters Health) - Children who spend time in day care centers or have many siblings may have a lower risk of developing seasonal allergies but an increased risk of asthma, according to the results of a European study.

The results support the so-called "hygiene hypothesis," which holds that exposure to bacteria, viruses and other microbes early in life helps steel the developing immune system against potentially allergy-causing proteins or allergens. But early exposure to these same irritants and resulting infections may damage the lungs and make a child more likely to develop asthma.

Other studies, however, have found that day care and siblings seem to protect against asthma, a chronic respiratory disorder that is on the rise in the US and other developed nations.

The findings are based on interviews with more than 18,500 adults aged 20 to 44 from 36 countries in Europe, the US, Australia and New Zealand conducted by C. Svanes and colleagues from Haraldsplass Hospital in Bergen, Norway.

The researchers also measured levels of immunoglobin E, an immune system protein that interacts with inflammatory cells to produce many of the symptoms characteristic of allergies, in nearly 14,000 volunteers. The findings are published in the latest issue of the journal Thorax.

Children without any siblings who spent time in day care were less likely to develop seasonal allergies or hay fever when they grew up. Similarly, hay fever was less common in children with many siblings if they had parents with allergies, which normally would increase a child's likelihood of developing such allergies him or herself.

The risk of allergies declined as the number of siblings increased, adding support to the notion that exposure to other children may be protective for those who had already been exposed to allergens, the researchers conclude.

However, children with more than two siblings were more likely to have asthma as adults. Kids who had spent time in day care before the age of 5 were also more likely to have symptoms of asthma such as wheeze, the report indicates.

"The microbial challenge that other children represent might contribute to non-allergic immunological development and, at the same time, to more clinical infections including lower airways infections adversely affecting the lungs," Svanes and colleagues conclude.

SOURCE: Thorax 2002;57:945-950.

Reference Source 89

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