Interactive effects of heat and air pollution on mortality in Europe using small area data – Results of the exhaustion project

Abstract

Background and Aim: Studies on the interactive short-term health effects of heat and air pollution are limited and mostly carried out in cities thus providing limited evidence at national level and on the effects in suburban and rural areas. Methods: We used daily data on natural, cardiovascular and respiratory mortality, air temperature, particulate matter (PM2.5, PM10) and ozone (O3) for administrative small areas (municipalities) in five regions of Europe (Norway, England and Wales, Germany, Italy, and the Attica Region, Greece) during the warm season. We applied a two-stage design, where area-specific data were analyzed in the first stage with over-dispersed Poisson regression models, and a random-effects meta-analysis was conducted in the second. The interaction between temperature and air pollutants was analysed by a response-surface model with a tensor smoother. The study reports the effects of air temperature for an increase from 75th to 99th percentile by levels of air pollutants (95th percentile=high, 50th=medium, 5th=low). Results: Overall results showed an effect modification by PM2.5 in the relationship between heat and mortality. For an increase in mean temperature, the overall risk of natural mortality increased by 6.6% (95% CI: -1.9%, 15.8%), 10.9% (95% CI: 2.7%, 19.7%), and 14.2% (95% CI: 4.5%, 24.9%) at the low, medium, and high levels of PM2.5, respectively. Stronger heat effects were observed for respiratory mortality with high PM2.5 levels (25.0%; 95%CI: 6.4%, 46.9%). For O3 we found a suggestion of effect modification in the relationship between heat and mortality, with a trend in effect estimates for increasing levels of O3. Among the five regions some heterogeneity in effect estimates and in the impact of effect modification by air pollution was observed. Conclusions: Evidence of effect modification between heat and air pollutants on mortality during the warm period was found, with slightly heterogeneous patterns within regions.