Air pollution and stroke; effect modification by sociodemographic and environmental factors. A cohort study from Denmark

Aslak Harbo Poulsen; Mette Sørensen; Ulla Arthur Hvidtfeldt; Matthias Ketzel; Jesper H Christensen; Jørgen Brandt; Lise Marie Frohn; Jibran Khan; Steen Solvang Jensen; Thomas Lund; Ole Raaschou-Nielsen

doi:10.1016/j.ijheh.2023.114165

Air pollution and stroke; effect modification by sociodemographic and environmental factors. A cohort study from Denmark

Int J Hyg Environ Health. 2023 Jun:251:114165. doi: 10.1016/j.ijheh.2023.114165. Epub 2023 Apr 28.

Affiliations

¹ Work, Environment and Cancer, Danish Cancer Society Research Center, Strandboulevarden 49, 2100, Copenhagen, Denmark. Electronic address: Aslak@cancer.dk.
² Work, Environment and Cancer, Danish Cancer Society Research Center, Strandboulevarden 49, 2100, Copenhagen, Denmark; Department of Natural Science and Environment, Roskilde University, Universitetsvej 1, 4000, Roskilde, Denmark.
³ Work, Environment and Cancer, Danish Cancer Society Research Center, Strandboulevarden 49, 2100, Copenhagen, Denmark.
⁴ Department of Environmental Science, Aarhus University, Frederiksborgvej 399, 4000, Roskilde, Denmark; Global Centre for Clean Air Research (GCARE), Department of Civil and Environmental Engineering, University of Surrey, Guildford, UK.
⁵ Department of Environmental Science, Aarhus University, Frederiksborgvej 399, 4000, Roskilde, Denmark.
⁶ Department of Environmental Science, Aarhus University, Frederiksborgvej 399, 4000, Roskilde, Denmark; iClimate - interdisciplinary Centre for Climate Change, Aarhus University, Frederiksborgvej 399, 4000, Roskilde, Denmark.
⁷ Department of Environmental Science, Aarhus University, Frederiksborgvej 399, 4000, Roskilde, Denmark; Danish Big Data Centre for Environment and Health (BERTHA), Aarhus University, Frederiksborgvej 399, 4000, Roskilde, Denmark.
⁸ Centre of Social Medicine, University Hospital Bispebjerg-Frederiksberg, Nordre Fasanvej 57, 2000, Frederiksberg, Denmark; Department of Occupational and Social Medicine, Holbaek Hospital & Department of Public Health, University of Copenhagen, Denmark.
⁹ Work, Environment and Cancer, Danish Cancer Society Research Center, Strandboulevarden 49, 2100, Copenhagen, Denmark; Department of Environmental Science, Aarhus University, Frederiksborgvej 399, 4000, Roskilde, Denmark.

PMID: 37121155
DOI: 10.1016/j.ijheh.2023.114165

Abstract

Objectives: Air pollution increases the risk of stroke, but the literature on identifying susceptible subgroups of populations is scarce and inconsistent. The aim of this study was to investigate if the association between air pollution and risk of stroke differed by sociodemographic factors, financial stress, comorbid conditions, and residential road traffic noise, population density and green space.

Methods: We assessed long-term exposure to air pollution with ultrafine particles, PM_2.5, elemental carbon and NO₂ for a cohort of 1,971,246 Danes aged 50-85 years. During follow-up from 2005 to 2017, we identified 83,211 incident stroke cases. We used Cox proportional hazards model (relative risk) and Aalen additive hazards models (absolute risk) to estimate associations and confidence intervals (CI) between 5-year running means of air pollution at the residence and risk of stroke in population strata.

Results: All four pollutants were associated with higher risk of stroke. The association between air pollution and stroke was strongest among individuals with comorbidities, with shorter education, lower income and being retired. The results also indicated stronger associations among individuals living in less populated areas, and with low noise levels and more green space around the residence. Estimates of absolute risk seemed better suited to detect such interactions than estimates of relative risk. For example for PM_2.5 the hazard ratio for stroke was 1.28 (95%CI: 1.22-1.34) and 1.26 (95%CI: 1.16-1.37) among those with mandatory and medium/long education respectively. The corresponding rate difference estimates per 100,000 person years were 568 (95%CI: 543-594) and 423(95%CI: 390-456) CONCLUSION: The associations between air pollution and risk of stroke was stronger among individuals of lower socioeconomic status or with pre-existing comorbid conditions. Absolute risk estimates were better suited to identify such effect modification.

Keywords: Air pollution; Cohort study; Epidemiology; Green-area; Noise; Stroke.

MeSH terms

Air Pollutants* / analysis
Air Pollution* / adverse effects
Cohort Studies
Denmark / epidemiology
Environmental Exposure / analysis
Humans
Particulate Matter / analysis
Stroke* / epidemiology

Substances

Air Pollutants
Particulate Matter