Long term exposure to ambient air pollution and hospital admission burden in Scotland: 16 year prospective population cohort study.

Abstract

Air pollution is considered a major threat for global health and is associated with various health outcomes. Previous research on long term exposure to ambient air pollution and health placed more emphasis on mortality rather than hospital admission outcomes and was characterised by heterogeneities in the size of effect estimates between studies, with less focus on mental/behavioural or infectious diseases outcomes. In this study, we investigated the association between long term exposure to ambient air pollution and all cause and cause specific hospital admissions. This was a prospective cohort study. Individual level data from the Scottish Longitudinal Study (SLS) were linked to yearly concentrations of four pollutants (nitrogen dioxide (NO₂), sulphur dioxide (SO₂), particulate matter diameter ≤10 µm (PM₁₀) and particulate matter diameter ≤2.5 µm (PM_2.5)) at 1 km² spatial resolution using the individual's residential postcode for each year between 2002 and 2017. The study included 202 237 adult individuals aged ≥17 years. The associations between air pollution and all cause, cardiovascular, respiratory, infectious, mental/behavioural disorders and other cause hospital admissions were examined using multi-level, mixed effects, negative binomial regression. Higher exposure to NO₂, PM₁₀ and PM_2.5 was associated with a higher incidence of all cause, cardiovascular, respiratory and infectious hospital admissions before adjusting for the area of residence, and in fully adjusted models when considering cumulative exposure across time. In fully adjusted models, the incidence rate for respiratory hospital admissions increased by 4.2% (95% CI 2.1% to 6.3%) and 1.2% (95% CI 0.8% to 1.7%) per 1 µg/m³ increase in PM_2.5 and NO₂ pollutants, respectively. SO₂ was mainly associated with respiratory hospital admissions (incidence rate ratio (IRR)=1.016; 95% CI 1.004 to 1.027) and NO₂ was related to a higher incidence of hospital admissions for mental/behavioural disorders (IRR=1.021; 95% CI 1.011 to 1.031). Average cumulative exposure to air pollution showed stronger positive associations with higher rates of hospital admissions. The results of this study support an association between long term (16 years) exposure to ambient air pollution and increased all cause and cause specific hospital admissions for both physical and mental/behavioural illnesses. The results suggest that interventions on air pollution through stricter environmental regulations could help ease the hospital care burden in Scotland in the long term.