Summary
Early-life exposure to animals has long been debated as a potential risk or protective factor for childhood asthma, so this nationwide Swedish cohort study tracked over one million children born between 2001 and 2010 to clarify that relationship. By linking national registries for animal ownership, medical diagnoses, asthma medications, and socioeconomic factors, researchers compared asthma outcomes in children exposed to dogs or farm animals during their first year of life with those not exposed. Among both school-aged children (age 6) and preschool-aged children (ages 1–5), living with a dog early in life was associated with a modestly lower risk of asthma, particularly after age 3; school-aged children exposed to dogs had an odds ratio of 0.87, and older preschool-aged children had a hazard ratio of 0.90. Very young preschoolers (<3 years) saw no meaningful benefit. Farm animals showed an even stronger protective effect, cutting asthma risk by roughly 52% in school-aged children and 31% in preschoolers. Results remained consistent when limiting analyses to firstborn children. Taken together, the findings support the idea that early exposure to dogs and farm animals—especially in the first year of life—can reduce the likelihood of developing asthma by age 6, offering families and clinicians valuable guidance when considering early-life animal contact.
PMID: 26523822
DOI: 10.1001/jamapediatrics.2015.3219
Abstract
Importance The association between early exposure to animals and childhood asthma is not clear, and previous studies have yielded contradictory results.
Objective To determine whether exposure to dogs and farm animals confers a risk of asthma.
Design, Setting and Participants In a nationwide cohort study, the association between early exposure to dogs and farm animals and the risk of asthma was evaluated and included all children born in Sweden from January 1, 2001, to December 31, 2010 (N = 1 011 051), using registry data on dog and farm registration, asthma medication, diagnosis, and confounders for parents and their children. The association was assessed as the odds ratio (OR) for a current diagnosis of asthma at age 6 years for school-aged children and as the hazard ratio (HR) for incident asthma at ages 1 to 5 years for preschool-aged children. Data were analyzed from January 1, 2007, to September 30, 2012.
Exposures Living with a dog or farm animal.
Main Outcomes and Measures Childhood asthma diagnosis and medication used.
Results Of the 1 011 051 children born during the study period, 376 638 preschool-aged (53 460 [14.2%] exposed to dogs and 1729 [0.5%] exposed to farm animals) and 276 298 school-aged children (22 629 [8.2%] exposed to dogs and 958 [0.3%] exposed to farm animals) were included in the analyses. Of these, 18 799 children (5.0%) in the preschool-aged children’s cohort experienced an asthmatic event before baseline, and 28 511 cases of asthma and 906 071 years at risk were recorded during follow-up (incidence rate, 3.1 cases per 1000 years at risk). In the school-aged children’s cohort, 11 585 children (4.2%) experienced an asthmatic event during the seventh year of life. Dog exposure during the first year of life was associated with a decreased risk of asthma in school-aged children (OR, 0.87; 95% CI, 0.81-0.93) and in preschool-aged children 3 years or older (HR, 0.90; 95% CI, 0.83-0.99) but not in children younger than 3 years (HR, 1.03; 95% CI, 1.00-1.07). Results were comparable when analyzing only first-born children. Farm animal exposure was associated with a reduced risk of asthma in both school-aged children and preschool-aged children (OR, 0.48; 95% CI, 0.31-0.76, and HR, 0.69; 95% CI, 0.56-0.84), respectively.
Conclusions and Relevance In this study, the data support the hypothesis that exposure to dogs and farm animals during the first year of life reduces the risk of asthma in children at age 6 years. This information might be helpful in decision making for families and physicians on the appropriateness and timing of early animal exposure.
Fall T, Lundholm C, Örtqvist AK, Fall K, Fang F, Hedhammar Å, Kämpe O, Ingelsson E, Almqvist C. Early Exposure to Dogs and Farm Animals and the Risk of Childhood Asthma. JAMA Pediatr. 2015 Nov;169(11):e153219. doi: 10.1001/jamapediatrics.2015.3219. Epub 2015 Nov 2. PMID: 26523822.