Background Inconsistent results have been found on the association between air pollution and stroke mortality. Additionally, evidence on people who are potentially sensitive to air pollution-associated stroke mortality is limited.

Methods Daily stroke mortality of adults aged over 65 between 2003 and 2008 in Shanghai, China were collected. The time-stratified case-crossover approach was used to assess the association between daily concentrations of air pollutants including particles with size <10 µm, sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) and stroke mortality.

Results Both total-stroke and ischaemic-stroke mortalities were found to be significantly associated with all three air pollutants. Haemorrhagic stroke was significantly associated with SO₂ and NO₂ only. Substantial differences were observed for effect estimates of ischaemic-stroke mortality in relation to NO₂ among people with cardiac diseases compared with those without; for an increase of 10 μg/m³ in NO₂, the increase in ischaemic-stroke mortality was 7.05% (95% CI 1.92% to 12.17%) for people with comorbid cardiac diseases versus 0.60% (95% CI −0.49% to 1.68%) for those without. We did not find evidence of effect modification by hypertension and diabetes.

Conclusions This study provides new evidence for the association between exposure to ambient air pollution and stroke mortality. Our results also suggest that underlying cardiac disorder may increase the risk for ischaemic-stroke mortality in relation to air pollution exposure, especially NO₂.

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