Ischaemic heart disease mortality and weather temperature in Barcelona, Spain

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 ar e exceptional, has been less investigated. To further contribute to these i ssues 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 temp erature, relative humidity and air pollutants were the covariates. We also controlled for influenza epidemics and annual seasonality. In order to rela x the restrictive assumptions (functional form and normality) imposed by th e 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 an d IHD existed. Our results suggested a temperature threshold (estimated in 21.06 degrees C) in the relationship between IHD and weather temperature. T he estimated value of the threshold was higher (23 degrees C) for very humi d days (relative humidity above 85%). The risk of an IHD death increased ap proximately 2.4% with every 1 degrees C drop of temperature below 4.7 degre es C and approximately 4% with every 1 degrees C rise above 25 degrees C. C onclusion: Our findings corroborated that not only the threshold but also t he 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.