According to a new study, strokes are affected by the body's internal clock.
Some types of strokes are more common in the morning than the evening, finds the paper published in the Journal of Neurology, Neurosurgery and Psychiatry.
Circadian rhythm – the body clock – appears to cause two peak times of day for strokes to occur. The first is between 06:00 and 08:00 and the second between 18:00 and 20:00.
Apparently, sleep causes a "significant dip in the numbers of strokes", although one in five cases of stroke caused by cerebral infarction occurred during sleep, mostly concentrated in the period immediately before waking up.
Almost 13,000 patients were observed for the study, which looked at three different kinds of stroke: subarachnoid haemorrhage; cerebral infarction; and intracerebral haemorrhage. All showed peak times of day.
Strokes caused by cerebral infarction had a higher peak in the morning and a lower peak in the afternoon than the other two types.
There was little variation between the men and women for peak times.