The modification effect of ozone pollution on the associations between heat wave and cardiovascular mortality

Abstract

<p>Epidemiological evidence concerning whether ozone modifies the impact of heat waves remain unexplored, especially in developing countries. To comprehensively evaluate the potential modification effect of ozone on heat wave impacts in warm seasons, we adopted a dataset (including mortality from overall cardiovascular diseases, chronic heart diseases and cerebrovascular diseases) in 250 Chinese cities from 2015 to 2019. A conditional quasi-Poisson regression model within the framework of the space-time-stratified case-crossover design was applied to obtain province-level associations, and a meta-analysis was adopted to pool province-level associations to national-average associations. Ozone concentration was categorized into low, medium and high levels using the 33rd and 66th percentiles of the location-specific levels as cutoffs, then we calculated the effect of heat waves in various ozone strata. Further stratification analyses on sub-populations (age group, sex and occupation) and regions were carried out. Heat waves were found to be positively associated with mortality from overall cardiovascular diseases (<i>RR</i>=1.043, 95% <i>CI</i>: 1.027-1.059). Higher concentrations of ozone significantly enhanced the effects of heat waves on cerebrovascular mortality. The mortality risk of heat waves was 1.071 (95% <i>CI</i>: 1.036-1.108) and 1.069 (95% <i>CI</i>: 1.039-1.100) at the medium and high levels, respectively (<i>P</i> for interaction=0.012 and 0.040, compared to the low level). A significant modification effect of ozone on the cerebrovascular mortality impact of heat waves was observed among people over 75, males and farmers, as well as in southern China and temperate climatic zones. Our findings suggest that ozone might potentially modify the mortality effect of heat waves.</p>