April 8, 2010

Dogs May Increase Asthma Risk For Children

A new study suggests that children with a higher-than-average risk of asthma are in danger of developing the lung disease if they have a dog around the house.

The study found that those who were exposed to high levels of dog allergens at the age of 7 were more likely to have asthma.

However, the study indicated that there was no relationship between cat-allergen exposure and a child's risk of asthma.

The findings, which were published in the journal Pediatric Allergy and Immunology, followed 380 children at increased risk of asthma due to family history.

It was not entirely made clear why dogs were related to a higher risk of asthma and cats were not.  But lead researcher Dr. Chris Carlsten of Vancouver General Hospital in British Columbia, Canada said one factor might be endotoxin, a substance produced by bacteria that triggers inflammation in the airways.

Carlsten and his colleagues discovered that children exposed to dog allergen at home were not at increased risk of developing an immune-system sensitization to dog allergen itself.  As a result, greater exposure to endotoxin might partly explain the association between having a dog in the home and a child's risk of asthma.

"Dogs tend to have a lot of endotoxin on them, because they're dogs," Carlsten told Reuters Health. In contrast, cats have much less, he said.

Carlsten said this does not answer the question of should families with a history of asthma or allergies opt for a kitten over a puppy.

"This study doesn't answer it," Carlsten said. "And in general, there is not enough evidence to recommend for or against pets."

He said that his advice to parents is to base the decision on their family's desire to have a pet, rather than the potential effects on asthma risk.

In the study, the children's mothers were recruited during pregnancy and researchers measured the levels of three allergens in the families' homes, including cat, dog and dust mites.  These levels were checked periodically over the child's first year of life and again when they were 7 years old.

About half of the families were randomly assigned to an intervention aimed at lowering the child's risk of developing allergies and asthma.   This included encouraging mothers to breastfeed for at least four months, as well as having their parents limit their child's exposure to dust mites, pets and tobacco smoke.

The researchers found that exposure to higher levels of dog allergen at age 7 associated with a nearly three-fold increase in the risk of asthma compared with lesser dog-allergen exposures.  However, that was only amongst children in the intervention group.

The risk of asthma was not associated with either cat nor dust-mite exposure in infancy or at age 7.  Children that had high dust-mite exposures were more likely to show sensitization to dust-mite allergen.

Carlsten said the findings underscore the complexity of the relationship between indoor-allergen exposures and children's asthma risk.  He said that more research is still needed to understand those intricacies.

The current study included children that were only at elevated risks of asthma, which means it is not clear whether the findings might also apply to children at average risk.


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