Abstract
There is observational evidence that children exposed to dogs in early life are at lower risk of asthma. It is unknown whether this association is modified by dog characteristics such as sex, breed, number of dogs, and dog size. The aim of this study was to determine whether different dog characteristics modify the risk of asthma among children exposed to dogs during their first year of life. In the main analysis, we used national register data for all children born in Sweden from Jan 1st 2001 to Dec 31st 2004 with a registered dog in the household during their first year of life (n = 23,585). We used logistic regression models to study the association between dog characteristics and the risk of asthma or allergy diagnosis and medication at age six. The prevalence of asthma at age six was 5.4%. Children exposed to female dogs had lower risk of asthma compared to those exposed to male dogs, odds ratio, OR = 0.84 (95% confidence interval, CI 0.74 to 0.95). Children with two dogs or more had lower risk of asthma than those with one dog only, OR = 0.79 (95% CI 0.65 to 0.95). Children whose parents had asthma and allergy had a higher frequency of exposure to dog breeds anecdotally described as “hypoallergenic” compared to those parents without asthma or allergy (11.7% vs 7.6%, p < 0.001). Exposure to these breeds were associated with higher risk of allergy OR = 1.27 (95% CI 1.02 to 1.59) but not asthma. In conclusion, we found evidence of an association between the sex of dog and the number of dogs with a lower risk of childhood asthma in dog-exposed children.
Highlights
Childhood asthma is a global public health concern
We use national registers of dog ownership combined with child and parental health data to assess whether dog characteristics such as sex, breed, number of dogs or size of the dog modifies the future risk of asthma among children exposed to dogs during their first year of life
Children exposed to female dogs during their first year of life were found to be at lower risk for asthma at age six than those exposed to male dogs, adjusted OR 0.84 (0.74, 0.95) (Table 2)
Summary
Childhood asthma is a global public health concern. About 54% of affected patients are sensitized to mammalian allergens at age 19, compared to about 21% of non-asthmatic individuals[1] and many affected children suffer from asthma exacerbation after pet exposure[2]. Increasing evidence shows that exposure to dogs during early childhood is associated with lower risk of asthma, for example, a 13% risk reduction in our recent study including 276,298 children[3]. The reason for this inverse relationship is not clear, and several factors may come into play. We use national registers of dog ownership combined with child and parental health data to assess whether dog characteristics such as sex, breed, number of dogs or size of the dog modifies the future risk of asthma among children exposed to dogs during their first year of life
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