JMIR Publications

ABSTRACT

Background:

The associations of long-term exposure to air pollutants with incidence of asthma remain inconclusive and the joint effects of air pollutants as a mixture is unclear.

Objective:

To examine the individual and joint association of long-term exposure to air pollutants with asthma incidence.

Methods:

Data was derived from the WHO SAGE (World Health Organization Study on Global Ageing and Adult Health) cohort study during 2007-2018. Annual average ambient daily eight-hour maximum ozone concentrations (MDA8 O3) and fine particulate matter (PM2.5) at individual residential address were estimated by an iterative random forest model and a satellite-based spatiotemporal model, respectively. The individual associations of PM2.5 and MDA8 O3 with asthma were estimated by a Cox proportional hazards regression model, and the joint association was estimated by a Quantile g-Computation model.

Results:

A total of 8,490 adults over 50 years old were included. Individual effect analyses showed that the risk of asthma was positively associated with MDA8 O3 (HR=1.12, 95%CI: 1.01 to 1.24, for per quantile) and PM2.5 (HR=1.18, 95%CI:1.05 to 1.31, for per quantile). Joint effect analyses showed that per equal quantile increment of MDA8 O3 and PM2.5 was associated with a 18% (HR=1.18, 95%CI:1.05 to 1.33) increase in the risk of asthma, and PM2.5 contributed more (68%) in the joint effects. The individual PAFs of asthma attributable to PM2.5 and MDA8 O3 were 2.86% and 4.83%, respectively, while the joint PAF of asthma attributable to exposure mixture was 4.32%.

Conclusions:

Long-term exposure to PM2.5 and MDA8 O3 may individually and jointly increase the risk of asthma, and the joint effects were smaller than the sum of individual effects.