[Myocardial infarct and geomagnetic disturbances: analysis of data on morbidity and mortality].

Relationships between different parameters of the geomagnetic activity and medical statistical data on myocardial infarction were investigated anew, because previous results in this field have been often inconsistent. The data are daily numbers of myocardial infarction incidence rates (15,543 cases) and number of deaths for infarction (3,065 cases), abstracted from registries of the 14 biggest hospitals of St. Petersburg (1989-1990). The analysis showed a statistically significant increase in myocardial infarction rate during big geomagnetic disturbances, defined by the days of the descending phase of cosmic ray Forbush decreases. An overall estimation of the average increase in infarction incidence rate during big geomagnetic storms, (10.5 +/- 1.2)%, has been computed by taking into account previous results [1-3]. In contrast, morbidity data did not show any significant correlation with geomagnetic disturbances. It was found also that the infarction incidence rate appears to be rather constant from Monday to Friday and to decrease sharply by a factor approximately 1.25 on Saturday-Sunday and mid-week festivities. This effect is associated with different exposure during work days and week-ends to man-made magnetic field environment mainly produced by electrified transport. Such effect was not observed in mortality data. The results and their methodological aspects are placed in the context of studies on possible health effects of low frequency magnetic fields both natural and man-made origin.