Long-term exposure to low concentrations of air pollution and cause-specific mortality beyond cardiorespiratory disease: A Danish nationwide cohort study

Abstract

BACKGROUND AND AIM: The association between air pollution and mortality from cardiorespiratory disease is well established, yet evidence for other causes is limited. We examined the associations of long-term exposure to air pollution with mortality from lower respiratory infection (LRI), diabetes, dementia, Alzheimer’s disease (AD), and psychiatric disease (PD) in a Danish nationwide cohort study. METHODS: We linked 3,083,227 subjects aged ≥30 years in 2000 to the Danish Cause of Death Registry until 2017. Annual mean concentrations of fine particulate matter (PM₂.₅), nitrogen dioxide (NO₂), and black carbon (BC) in 2010 at 100x100m resolution were estimated with European-wide hybrid land-use regression models developed within ELAPSE (Effects of Low-Level Air Pollution: A Study in Europe). We applied Cox proportional hazard models with age as time scale, parish as cluster, and adjusting for sex, country of origin, income, education, employment status, marital status, and parish and region-level indicators of income and employment. RESULTS:During the follow-up, 805,838 subject died: 30,578 from LRI, 20,735 from diabetes, 41,178 from dementia, 11,894 from AD, and 12,801 from PD. Mean levels of PM₂.₅, NO₂ and BC were 12.4 µg/m³, 20.3 µg/m³ and 1.0 10⁻⁵/m, respectively. Hazard ratios (95% confidence intervals) for associations of PM₂.₅, NO₂, and BC with LRI mortality were 1.16 (1.10-1.21) per 5 µg/m³, 1.07 (1.04-1.09) per 10 µg/m³, and 1.05 (1.03-1.08) per 0.5 10⁻⁵/m, respectively. Corresponding estimates for diabetes mortality were 1.11 (1.04-1.17), 1.03 (1.00-1.05), and 1.00 (0.98-1.03); for dementia mortality were 1.05 (1.00-1.10), 1.05 (1.03-1.07), and 1.03 (1.01-1.05); for AD mortality were 1.24 (1.14-1.36), 1.18 (1.13-1.22), and 1.15 (1.11-1.19); and for PD mortality were 1.39 (1.28-1.51), 1.24 (1.20-1.28), and 1.22 (1.18-1.27). CONCLUSIONS:Long-term exposures to PM₂.₅, NO₂, and BC were associated with mortality other than cardiorespiratory diseases, even stronger for mortality from Alzheimer’s and psychiatric disease. The indirect adjustment for missing risk factors will be applied. KEYWORDS: Air pollution, Big data, Long-term exposure, Mortality, Neurodegenerative outcomes