Diurnal and seasonal variations in the occurrence of stroke: a community-based study.

Several hospital-based studies suggest a circadian rhythm for stroke, with a peak of onset in the morning. To verify whether these results could be confirmed in a community-based study, we used data from the SEPIVAC, a community-based stroke register in Umbria, Italy. Cerebral infarctions (48%), primary intracerebral hemorrhages (54%), subarachnoid hemorrhages (53%) and 'not known' strokes (51%) were all more common between 6 a.m. and noon, and this peak was still present when strokes recognized on awakening were evenly redistributed over the sleep period. Looking at the subgroups of cerebral infarction, lacunar syndromes were more common during sleep. Cerebral infarctions were more frequent during winter, and primary intracerebral hemorrhages during autumn.