Ambient air pollution and asthma onset in Taiwanese adults.

BACKGROUND: Ambient nitrogen dioxide is associated with asthma occurrence in adults in Western countries. However, two recent large-scale studies have provided inconclusive results regarding this association. Moreover, the association remains unknown in an Asian population. OBJECTIVE: We aimed to investigate the association between ambient air pollution exposure and incident adult asthma. METHODS: From 2016 to 2017, we conducted a cross-sectional self-administered questionnaire survey with retrospective follow-up of incident asthma cases among schoolchildren's parents from 41 schools within 1 km of air monitoring stations distributed throughout the main island of Taiwan. To estimate participants' exposure, air pollution data of air monitoring stations within 1 km of schools from where participants were sampled were inputted into the proximity model. We used mixed logistic regression models to determine the association between air pollution exposure and asthma onset within five years prior to the survey. RESULTS: The questionnaire was completed for a total of 11 585 participants out of 13 424 candidates (response rate, 86.3%). Among 9131 participants aged from 26 to 50 years, 101 were diagnosed with asthma within the five years prior to the survey. The prevalence of incident asthma cases was 2.2 per 1000 person-years. Those exposed to higher ambient nitrogen dioxide (odds ratio = 1.20 per interquartile [5.7 ppb] of nitrogen dioxide, 95% CI = 1.02-1.42) were more likely to develop adult-onset asthma. CONCLUSION: In an Asian population, exposure to higher ambient nitrogen dioxide is associated with increased prevalence of incident asthma cases among adults aged 26-50 years.