Individual and combined effects of indoor home exposures and ambient PM2.5 during early life on childhood asthma in us birth cohort studies

Abstract

Background: Children encounter multiple indoor and outdoor environmental exposures in early life. We assessed the independent effects of indoor home exposures and ambient particulate matter with an aerodynamic diameter ≤2.5 µm (PM_2.5) on early childhood asthma diagnosis.

Methods: We included 6,413 children born 1987-2016 from nine United States prospective birth cohorts from the Environmental Influences on Child Health Outcomes consortium, with complete covariate and outcome data. Exposures were (1) average ambient PM_2.5 levels during the first 3 years of life, and (2) indoor home exposures, including water damage/home dampness during infancy/childhood, dogs/cats at home during infancy, dust mite allergen during infancy/childhood. Asthma was defined as caregiver-reported or doctor-diagnosed asthma anytime from birth to age 5. We applied Cox proportional hazards models, adjusting for individual-level and neighborhood-level confounders. Cohort-specific effects were implemented as fixed effects.

Results: By age 5 years, 10.3%-50.3% of children had developed asthma across general-risk and high-risk cohorts. We found a significant detrimental association of PM_2.5 and water damage/home dampness, and a protective association of dogs in the home with risk of childhood asthma, regardless of PM_2.5 adjustment. The effect of having both water damage/home dampness and high PM_2.5 on asthma diagnosis was greater than that of no water damage/home dampness and having low PM_2.5 (hazard ratio: 1.95 [95% confidence interval = 1.19, 3.20]). There were no significant associations with household cats or dust mites.

Conclusion: Multiple early exposures, such as PM_2.5, home dampness, and absence of dogs in the home, should be considered together as risk factors for childhood asthma.

Keywords: Air pollution; Asthma; Childhood asthma; PM2.5; Pets; Water damage/home dampness.