Time of sunrise and hours with daylight may have an effect on the seasonality and diurnal variation of heart attack

Background The time of onset of myocardial infarction shows seasonal and daily variation. We aimed to investigate whether the number of hours with daylight has an effect on the seasonal variation of heart attack, and whether the time of sunrise has an effect on the diurnal rhythm of myocardial infarction.Methods We carried out a retrospective database study covering all patients admitted to any acute care hospital with the diagnosis of myocardial infarction in Hungary between January 2004 and December 2005 (n=32 329). Data were collected from the National Health Insurance Fund Administration (OEP) according to the International Classification of Diseases (ICD 121,122) and National Meteorology Service (OMSZ). In case of patients who occurred in the database several times the events have been considered as a separate case.Results With consideration to seasonal variation, the peak period of heart attack was found in the spring, with the lowest number of events in the summer. The number of hours with daylight showed a weak negative correlation with the occurrence of myocardial infarction (r=-0.108, P <0.05). With respect to diumal variation, the peak period of daily events was between 6-12 in the morning (35.57%). We have found a positive correlation between the time of sunrise and sunset and the occurrence of myocardial infarction (P<0.01).Conclusion Based on our findings, the number of hours with daylight and the time of sunrise may be connected with the chances of having heart attack; however other factors, such as high blood pressure, diabetes or smoking may also have an influence.