The Timing of Modifiable Environmental Exposures during Childhood Affects the Age of Asthma Development

Background: Childhood asthma is a multifactorial condition influenced by hereditary and modifiable environmental traits. Objective: I investigated longitudinal associations between childhood asthma development and three modifiable environmental exposures: maternal second-hand smoke exposure in pregnancy, neighborhood walkability, which captures community features that promote walking, and material deprivation, a comprehensive measure of socioeconomic status. Methods: In a population-based cohort of 5619 seven-year-old Toronto children, parents reported age of physician-diagnosed asthma development and maternal active and passive smoking in pregnancy. Administrative data housed at the Institute for Clinical Evaluative Sciences described the 1997-2003 Toronto birth cohorts (326 383 children). Home neighborhood walkability and deprivation quintiles were reported in validated indices and incident asthma was defined by time of entry into the validated Ontario Asthma Surveillance Information System (OASIS) database. The associations between incident asthma and the exposures were measured using Cox proportional and discrete-time hazard survival analysis. The associations between asthma visits and walkability or deprivation in each year of life were measured using Generalized Estimating Equations and generalized linear mixed models. Results: In the population-based cohort, 15.5% of children developed asthma. Children of non-smoking mothers with home second-hand smoke exposure during pregnancy were more likely to develop asthma (HR 1.34; 95% CI, 1.01-1.76). In the administrative data cohort, OASIS asthma criteria were met for 21% of children. Low birth neighborhood walkability (HR 1.11; 95% CI, 1.08-1.14) and high birth neighborhood deprivation (HR 1.11; 95% CI, 1.09-1.13) were associated with increased risk of incident asthma. These trends persisted for currently-symptomatic incident asthma, lifetime exposure to low walkability or high deprivation and healthcare visits for asthma in each year of life. Conclusions: Home second-hand smoke exposure for non-smoking mothers during pregnancy is associated with incident childhood asthma. Children living in neighborhoods with low walkability or high deprivation are also at increased risk of asthma.Ph.D.2018-03-22 00:00:0