Modification of the effect of ambient air temperature on cardiovascular and respiratory mortality by air pollution in Ahvaz, Iran

Objectives The aim of this study was to investigate the modification of temperature effects on cardiovascular and respiratory mortality by air pollutants (particulate matter less than 2.5 µm and 10 µm in diameter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), sulphur dioxide (SO2)). Methods Poisson additive models combined with penalized distributed lag non-linear model (DLNM) were used to assess the association of air temperature with daily number of deaths from cardiovascular and respiratory diseases in Ahvaz, Iran from March 21, 2014 to March 20, 2018, while controlling for day of the week, holiday, relative humidity, wind speed, air pollutants, and seasonal and long-term trend. Subgroup analyses were conducted to evaluate the effect modification for gender and age groups. To assess the effect modification by air pollutants on temperature effects, each air pollutant was categorized into two levels (> median value and ≤ median value). Results Overall, there was no significant association between temperature and cardiovascular and respiratory mortality. but, in subgroup analyses hot temperatures was significantly associated with increased risk of cardiovascular mortality among ≥75 years (the strongest effect was seen in lag 0). Overall, the results revealed that there were no interactive effects between temperature and air pollutants on cardiovascular and respiratory mortality. Conclusion There is a weak, yet significant association between hot temperature and cardiovascular mortality, but only in elderly people. Overall, there was no modification of the effect of ambient temperature on cardiovascular and respiratory mortality by air pollution.