Outdoor nitrogen dioxide exposure and longitudinal health status trajectory in the Canadian National Population Health Survey

Few studies have examined the association between air pollution and the trajectory of global health status measures related to the functional impacts of chronic disease. To address this gap, we examined the trajectory of the Health Utilities Index (HUI) over 17 years of follow-up among Canadian National Population Health Survey (NPHS) participants. Annual average nitrogen dioxide (NO₂) exposures from a national land use regression surface were mapped to 15,631 NPHS participants at their place of residence provided at each follow-up. We modelled HUI trajectory as a cubic polynomial function of age in relation to air pollution and selected covariates using random growth curve models to account for longitudinal repeated measures. Adjusting for covariates selected based on a directed acyclic graph, we found that NO₂ exposure exhibited a significant negative association with HUI in females. It also exhibited a significant positive interaction with the linear age term, and a significant negative interaction with the quadratic age term, resulting in a small non-significant decrease in quality adjusted life years lived after age 20 among females. Our analysis provides a proof of concept for examining the influence of built environment variables on the trajectory of health related quality of life in Canada.