Synergy in the effects of temperature and air pollution on mortality in 8 European cities. Results from the PHASE project.

Abstract

Background: Numerous studies have associated excess heat or cold with increased mortality. Air pollution, especially particulate matter and ozone also deteriorate human health. Their joint effects, though, are less well studied and understood. Aim: Within the PHASE project, we used data from 8 European cities (Athens, Barcelona, Budapest, Helsinki, Paris, Rome, Stockholm and Valencia) to investigate possible synergistic effects of temperature and air pollution on mortality. Methods: City-specific Poisson regression models controlling for seasonality and other confounders were used separately for summer (April-September) and winter (October-March). Maximum apparent temperature was the exposure variable in summer, while minimum was used in winter. Based on previous results, threshold terms for summer and linear temperature terms for winter were used. Interaction terms between temperature and pollution variables were included in the models to investigate synergy on all cause, cardiovascular and respiratory mortality, in all ages and by age group. Results: Initial results provide evidence for synergy in several participating cities. For example, significant positive interaction between high temperature and PM10 was found in Athens and Paris, concerning both total and cardiovascular mortality in all ages. In Athens, significant synergy was also detected between high temperature and ozone on cardiovascular mortality in all ages. In Paris and Stockholm, a significant positive interaction between high temperature and ozone was found on total mortality in all ages. Conclusions: There is evidence for higher impact on mortality on days with both high temperature and high ozone or PM10 concentration, although this was not consistent across all cities. These findings should have implications on policy-making in Europe.