Air pollution, noise, greenspace and pneumonia, a nation-wide cohort study from Denmark

Abstract

Ambient air pollution, traffic noise, and residential green space have each been linked to respiratory health, including pneumonia. Exposure correlation make mutual confounding a concern. We investigated long-term associations between these exposures and pneumonia incidence in a nationwide Danish cohort. We included all residents aged ≥35 years, without prior pneumonia, followed from 2010 to 2017. We estimated 5-year mean residential exposures to PM2.5, nitrogen dioxide (NO2), elemental carbon (EC), ultrafine particles (UFP), road traffic noise, and percentage green space within 150m and 1000m of the home. Exposure-response relationships were assessed using Cox proportional hazards models, linearly and with natural cubic splines, adjusting for time-varying individual and area-level covariates and exposures. Among 2 418 958 individuals contributing 16.8 million person-years, 159 724 pneumonia cases occurred. In linear analysis Hazard ratios (HR) per interquartile range (IQR) were 1.22 (95 % confidence interval: 1.20–1.23) for PM2.5, 1.15 (1.14–1.16) for NO2, 1.13 (1.12–1.14) for UFP, and 1.04 (1.03–1.4) for EC. For all air pollutants spline analysis showed non-linear associations with strongest association per unit change at lower concentrations. Noise and reduced green space within 150 m showed weaker positive associations. Adjustment for air pollution attenuated the effects of noise and green space, while associations for PM2.5, NO2, and UFP were robust to adjustment for noise and green space but sensitive to adjustment for air pollutants. Our findings suggest that long-term exposure to PM2.5, NO2, and UFP may increases the risk of pneumonia, independent of traffic noise and green space, which may act as weaker, independent risk factors