Ischaemic heart disease mortality and weather temperature in Barcelona, Spain

Abstract

Background: Association between ischaemic heart disease (IHD) mortality and extreme values of weather temperature has been the focus of many previous studies. To what extent moderate changes in temperature also influence IHD mortality in milder regions, where either low temperatures or heat waves are exceptional, has been less investigated. To further contribute to these issues we have investigated the association between weather temperature and IHD in Barcelona, Spain. Methods: A transfer function model was specified. The dependent variable was the daily time series of IHD while, weather temperature, relative humidity and air pollutants were the covariates. We also controlled for influenza epidemics and annual seasonality. In order to relax the restrictive assumptions (functional form and normality) imposed by the transfer function, this was modelled non-parametrically. The influence of unusual periods and outliers of weather temperature and humidity was also assessed. Results: A non-linear relationship between weather temperature and IHD existed. Our results suggested a temperature threshold (estimated in 21.06°C) in the relationship between IHD and weather temperature. The estimated value of the threshold was higher (23°C) for very humid days (relative humidity above 85%). The risk of an IHD death increased approximately 2.4% with every 1°C drop of temperature below 4.7°C and approximately 4% with every 1°C rise above 25°C. Conclusion: Our findings corroborated that not only the threshold but also the magnitude of the association presents a different range depending on the latitude, and is wider for southern locations. We suggest that the effect of temperature could account for the regional variations in IHD mortality.