Influence of the Thermal Environment on IHD Mortality and Morbidity in Germany (2001-2010)

There is some evidence from the literature that the atmospheric environment influences the frequency of acute cardiovascular problems. In our study we analyzed the influence of meteorological parameters on the occurrence of ischemic heart diseases (IHD, ICD codes I20-I25), a subgroup of cardiovascular diseases in Germany. Data on the daily occurrence of IHD death rates and hospital admission rates were provided for the period 2001-2010 on a regional resolution of NUTS2 for Germany by the Federal Research Data Center. In total about 7.5 million cases of hospital admissions and about 1.5 million IHD deaths occurred in the studied period. We analyzed total IHD mortality (ICD codes I20 – I25), for women and men separately as well as the subgroups I20-I22 (mainly myocardial infarctions) and I24-I25 (other acute and chronic ischemic heart diseases). Since the daily numbers of IHD deaths and/or hospital admissions were low in several regions, these regions were aggregated for data protection reasons. Daily mortality rates were detrended and corrected for the course of the year. Morbidity data were additionally corrected for the weekly course. We found a strong relationship between the thermal environment and daily mortality rates. In order to describe the thermal environment we used daily averages of air temperature, perceived temperature and humidex. The differences in the shape and strength of the relationship between these parameters / indexes and IHD mortality were small. Therefore results are described for daily mean temperature. The detrended mortality data that were not corrected for the course of the year, showed the typical V-or U-shape relationship with the thermal environment. The lowest mortality rates occurred at daily mean temperatures between 15°C and 19°C. Below and above this range, mortality increased nearly linearly. We found that the increase below this thermal optimum was mainly due to the seasonal feature. The mortality rates that were corrected for the course of the year didn't show any increase in mortality below the optimum temperature. An exception was the mortality with ICD codes I20-I22 (mainly myocardial infarctions) that was increasing also after correction for the course of the year at very low daily mean temperatures (< -7°C). Apart from absolute values of air-temperature we also analyzed the influence of changes compared to the previous day. The relative risk of IHD mortality increased for increases of air-temperature of more than 5°C for men and ICD codes I24-I25 (other acute and chronic ischemic heart diseases) and for decreases of more than 3°C for women and ICD codes I24-I24 and of more than 5°C also for men and ICD codes I20-I22. We couldn't find any significant relationship between the number of hospital admissions due to ischemic heart diseases and the analyzed meteorological parameters.

We also analyzed the increase in morbidity and mortality during heat-waves. A heat wave in this study was identified when at least three consecutive days exceeded the 97.5th percentile of daily mean temperature. During heat waves the daily risk for IHD mortality increased on average by 15 %. Women were more affected than men (women: 19 %, men: 11 %).We couldn't find any increase in the number of hospital admissions during heat-waves. This was the first study analyzing the relationship between IHD morbidity and mortality all over Germany. We were able to demonstrate that there is a significant increase in IHD mortality in Germany especially on days with high average temperatures and heat-waves. The high numbers of IHD mortality rates in winter show only little relationship to average temperatures when corrected for the course of the year. A potential relationship between the atmospheric environment and IHD morbidity remains unclear.

Acknowledgments: This work was funded by the Federal Environment Agency and the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety as part of the project UFOPLAN-371161238 “Climate change, bioclimatology and health effects” (2012-2014), embedded in the German Adaptation Strategy to climate change.