Association between air pollution and daily mortality and hospital admission due to ischaemic heart diseases in Hong Kong

Ischaemic heart disease (IHD) is one of the leading causes of death worldwide. The effects of air pollution on IHD mortalities have been widely reported. Fewer studies focus on IHD morbidities and PM2.5, especially in Asia. To explore the associations between short-term exposure to air pollution and morbidities and mortalities from IHD, we conducted a time series study using a generalized additive model that regressed the daily numbers of IHD mortalities and hospital admissions on daily mean concentrations of the following air pollutants: nitrogen dioxide (NO2), particulate matter with an aerodynamic diameter less than 10 μm (PM10), particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5), ozone (O3), and sulfur dioxide (SO2). The relative risks (RR) of IHD deaths and hospital admissions per 10 μg/m3 increase in the concentration of each air pollutant were derived in single pollutant models. Multipollutant models were also constructed to estimate their RRs controlling for other pollutants. Significant RRs were observed for all five air pollutants, ranging from 1.008 to 1.032 per 10 μg/m3 increase in air pollutant concentrations for IHD mortality and from 1.006 to 1.021 per 10 μg/m3 for hospital admissions for IHD. In the multipollutant model, only NO2 remained significant for IHD mortality while SO2 and PM2.5 was significantly associated with hospital admissions. This study provides additional evidence that mortalities and hospital admissions for IHD are significantly associated with air pollution. However, we cannot attribute these health effects to a specific air pollutant, owing to high collinearity between some air pollutants.