SEASONAL-VARIATION IN STROKE INCIDENCE IN HISAYAMA, JAPAN

We investigated seasonal variation in the incidence of cerebral stroke among the general population aged >40 years in November of 1961 in Hisayama, Japan. During the 24-year follow-up period, 311 cases of cerebrovascular diseases occurred. The date or month of onset was determined in 308 cases, of which 51 were classified as intracerebral hemorrhage, 223 as cerebral infarction, and 27 as subarachnoid hemorrhage. We observed a significant seasonality in the incidence of all stroke (p<0.01), of intracerebral hemorrhage (p<0.05), and of cerebral infarction (pcO.Ol), whereas subarachnoid hemorrhage had no significant seasonal pattern. Subjects <64 years of age showed a significant seasonal variation in the incidence of both intracerebral hemorrhage (p<0.05) and cerebral infarction (p<0.01). A significant seasonal pattern for the incidence of intracerebral hemorrhage was also noted among persons with hypertension (p<0.05) or a high serum cholesterol level (p<0.05), whereas such a pattern for cerebral infarction was documented among normotensive persons (p<0.05) and those with a low serum cholesterol level (p<0.01). In addition, the incidences of intracerebral hemorrhage and cerebral infarction were negatively correlated with mean ambient temperature (p<0.01 and <0.05, respectively), and all stroke and intracerebral hemorrhage in men were significantly related to intradiumal temperature change (p<0,05 and p<0.01, respectively). The significance of the seasonal occurrence of stroke is discussed in relation to relevant risk factors. © 1990 American Heart Association, Inc.