Weekly variation and seasonal variation in the occurrence of stroke

Abstract

The frequency of occurrence of stroke at different seasons or on different days of the week was investi-gated in 794 patients with stroke who were admitted to our hospital between December 1991 and November 1996. They included 291 patients with brain hemorrhage and 503 with brain infarction. The brain infarction was classified according to criteria based on the clinical findings into atherothrombotic stroke (n=196), lacunar stroke (n=158), and cardioembolic stroke (n=149) . Careful histories were taken from the patient or a person who observed the onset to determine the day of the week on which the onset of stroke occurred. For atherothrombotic stroke, the incidence of stroke was high on Fridays, but low on Saturdays and Sundays (chi-square test for goodness of fit, p<0.02), particularly in working men younger than 65 years (p<0.1). For other types of stroke, there was no specific day of the week on which stroke was likely to occur. Winter was the peak season for brain hemorrhage (p<0.05). Seasonality was found in the older age group for lacunar stroke (p<0.1) and in the younger age group for brain hemorrhage (p<0.1) . These findings support the hypothesis that the onset of all types of stroke may be triggered by life circumstances, life cycle and changes of weather.