Evidence of the role of short-term exposure to ozone on ischaemic cerebral and cardiac events: the Dijon Vascular Project (DIVA)

Objectives To confirm the effects of short-term exposure to ozone (O₃) on ischaemic heart and cerebrovascular disease.

Methods Daily levels of urban O₃ pollution, the incidence of first-ever, recurrent, fatal and non-fatal ischaemic cerebrovascular events (ICVE) and myocardial infarction (MI) were correlated using a case-crossover design. The authors analysed 1574 ICVE and 913 MI that occurred in Dijon, France (150 000 inhabitants) from 2001 to 2007. Sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO) and particulate matter with an aerodiameter of ≤10 μg/m³ (PM₁₀) were used to create bi-pollutant models. Using the adjusted OR, the effects of O₃ exposure were calculated for every 10 μg/m³ increase in pollutants in multivariate logistic models adjusted for temperature, humidity, flu outbreaks and holidays.

Results The authors found a significant association between exposure to O₃ and recurrent ICVE with a 3-day lag (OR=1.115; 95% CI 1.027 to 1.209). The direction and magnitude of the association between exposure to O₃ and recurrent MI were similar but not statistically significant. For incident events, the authors detected only a non-significant association for ICVE with a 2-day lag (OR=1.041; 95% CI 0.996 to 1.089). In the subgroup analysis for ICVE, the authors observed an increased association with cardiovascular risk factors (OR=1.523; 95% CI 1.149 to 2.018). For MI, the authors found an association with O₃ when hypercholesterolaemia was present (OR=1.111; 95% CI 1.020 to 1.211), and the association became stronger with the number of cardiovascular risk factors. The authors found a marked dose–response relationship.

Conclusion Recurrent ICVE and MI could be triggered by short-term exposure to even low levels of O₃, especially among subjects with severe vascular risk factors.