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Rationale: Childhood asthma has shown variable associations with children's physical activity. Neighborhood walkability captures community features that promote walking and is protective against some chronic conditions, such as obesity and diabetes.Objectives: We evaluated associations between home neighborhood walkability and incident and ongoing childhood asthma.Methods: In this population-based cohort study, we used prospectively collected administrative healthcare data for the Province of Ontario housed at the Institute for Clinical Evaluative Sciences. We followed an administrative data cohort of 326,383 Toronto children born between 1997 and 2003, inclusive, until ages 8-15 years. Home neighborhood walkability quintile was measured using a validated walkability index with four dimensions: population density, dwelling density, access to retail and services, and street connectivity. Incident asthma was defined by time of entry into the validated Ontario Asthma Surveillance Information System database, which requires two outpatient visits for asthma within two consecutive years or any hospitalization for asthma and follows children with asthma longitudinally starting at any age. Associations between walkability and incident asthma were examined using Cox proportional hazards models. Associations between ongoing asthma and walkability in each year of life were examined using generalized linear mixed models.Results: Twenty-one percent of children (n = 69,628) developed incident asthma and were followed longitudinally in the Ontario Asthma Surveillance Information System database. Low birth home neighborhood walkability was associated with an increased incidence of asthma (hazard ratio, 1.11; 95% confidence interval, 1.08-1.14). Among children with asthma, low walkability in a given year of a child`s life was associated with greater odds of ongoing asthma in the same year (odds ratio, 1.12; 95% confidence interval, 1.09-1.14).Conclusions: Children living in neighborhoods with low walkability were at increased risk of incident and ongoing asthma. Neighborhood walkability improvement, such as by adding pedestrian paths to improve street connectivity, offers potential strategies to contribute to primary asthma prevention. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen dioxide (NO2), a surrogate measure of traffic-related air pollution (TRAP), has been associated with incident childhood asthma. Timing of exposure and atopic status may be important effect modifiers. We collected cross-sectional data on asthma outcomes from Toronto school children aged 5–9years in 2006. Lifetime home, school and daycare addresses were obtained to derive birth and cumulative NO2 exposures for a nested case–control subset of 1497 children. Presence of other allergic disease (a proxy for atopy) was defined as self-report of one or more of doctor-diagnosed rhinitis, eczema, or food allergy. Generalized estimating equations were used to adjust for potential confounders, and examine hypothesized effect modifiers while accounting for clustering by school. In children with other allergic disease, birth, cumulative and 2006 NO2 were associated with lifetime asthma (OR 1.46, 95% CI 1.08–1.98; 1.37, 95% CI 1.00–1.86; and 1.60, 95% CI 1.09–2.36 respectively per interquartile range increase) and wheeze (OR 1.44, 95% CI 1.10–1.89; 1.31, 95% CI 1.02–1.67; and 1.60, 95% CI 1.16–2.21). No or weaker effects were seen in those without allergic disease, and effect modification was amplified when a more restrictive algorithm was used to define other allergic disease (at least 2 of doctor diagnosed allergic rhinitis, eczema or food allergy). The effects of modest NO2 levels on childhood asthma were modified by the presence of other allergic disease, suggesting a probable role for allergic sensitization in the pathogenesis of TRAP initiated asthma. [Copyright &y& Elsevier]