The researchers examined 12,957 cases and said that the risk of a stroke was lowest during sleep. This may probably be due to changes in the body's internal clock, they speculated. Researchers from Iwate Medical University in Japan studied data on three different types of strokes.
Ischemic stroke, where blood flow to brain arteries is interrupted, was the most common, followed by hemorrhagic strokes. They found that all three types of strokes peaked two hours in morning and two hours in the evening.
The researchers say that variations in blood pressure may be the cause for the peaking time of strokes. Earlier studies have documented that blood pressure is highest in the morning and evening at given times. Reacting to the study, Joe Korner, of the Stroke Association said, "Previous studies have shown that stroke risk does vary over the 24 hour cycle and that occurrence during sleep is most common for ischaemic strokes. This new study confirms that finding. However, more information is required about the different subtypes of ischaemic stroke - there are several different types, each with very different causes."