The relationship between mortality caused by cardiovascular diseases and two climatic factors in densely populated areas in Norway and Ireland

Background Seasonal variations in mortality due to cardiovascular disease h ave been demonstrated in many countries, with the highest levels occurring during the coldest months of the year. It has been suggested that this can be explained by cold climate. In this study, we examined the relationship b etween mortality and two different climatic factors in two densely populate d areas (Dublin, Ireland and Oslo/ Akershus, Norway). Methods Meteorological data (mean daily air temperatures and wind speed) an d registered daily mortality data for three groups of cardiovascular diseas e for the period 1985-1994 were obtained for the two respective areas. The daily mortality ratio for both men and women of 60 years and older was calc ulated from the mortality data. The wind chill temperature equivalent was c alculated from the Siple and Passels formula. Results The seasonal variations in mortality were greater in Dublin than in Oslo/Akershus, with mortality being highest in winter. This pattern was si milar to that previously shown for the two respective countries as a whole. There was a negative correlation between mortality and both air temperatur e and wind chill temperature equivalent for all three groups of diseases. T he slopes of the linear regression lines describing the relationship betwee n mortality and air temperature were a lot steeper for the Irish data than for the Norwegian data. However, the difference between the steepness of th e linear regression lines for the relationship between mortality and wind c hill temperature equivalent was considerably less between the two areas. Th is can be explained by the fact that Dublin is a much windier area than Osl o/Akershus. Conclusion The results of this study demonstrate that the inclusion of two climatic factors rather than just one changes the impression of the relatio nship between climate and cardiovascular disease mortality. (C) 2000 Lippin cott Williams & Wilkins.