Association of living in a farming environment with asthma incidence in Canadian children

Abstract

Background: Living in a farming environment during early life has been shown to have a protective effect against asthma and this has given rise to the 9hygiene hypothesis9; however, only a limited number of longitudinal studies have been conducted to examine this relationship, to date. Objective: To examine the effect of living in a farm environment on asthma incidence in children in a population-based 14-year follow-up study. Methods: In total, 10,941 children free of asthma and wheeze at the baseline in the National Longitudinal Survey of Children and Youth were considered. Children9s living environment was classified, based on street-level frontage, into three categories: non-rural, rural non-farming and farming. Results: The 14-year cumulative incidence of asthma was 16.50%, 13.12%, and 10.18% for children residing in non-rural, rural non-farming, and farming environments, respectively. After adjusting for potential confounders, children residing in farming environments had a significantly reduced risk of asthma [hazard ratio (HR): 0.56; 95% confidence interval (CI): (0.41, 0.76)] in comparison to those living in non-rural environments. Children residing in rural non-farming environments also had a reduced risk of asthma in comparison to those living in non-rural environments. In an analysis, restricting to children aged 0 to 4 years and considering children living in rural non-farming environments as the comparison group, children living in farming environments had a reduced risk of asthma [HR = 0.59; 95% CI: (0.35, 0.99)]. Conclusion: Our study provides further evidence that living in a farming environment during childhood is protective of asthma incidence in adolescence and adulthood.