Strokes More Likely in Early Morning and Evening

A new study has found that strokes are most likely to occur during certain two-hour periods in the morning and in the evening.

Researchers from Iwate Medical University (IMU, Japan) analyzed a total of 12,957 cases of first-ever stroke onset in the Iwate Stroke Registry between 1991 and 1996, looking for patterns in the wake-sleep cycle. The researchers divided the day into 12 two-hour periods and found that the internal body clock appears to affect the timing, with risk peaking between 6-8 am and 6-8 pm. Risk was lowest when the patients were asleep.

The researchers examined three types of stroke: ischemic cerebral infarction (CIF), intracerebral hemorrhage (ICH), and subarachnoid hemorrhagic stroke (SAH), where bleeding is in the arteries on the brain's surface. The researchers found that the risk peaked for all three types of stroke during the morning and early evening. Ischemic strokes appeared more likely to occur in the morning and slightly less likely to occur during the evening peak slot, while hemorrhagic strokes showed less of a peak in the morning but a higher peak in the evening. The study appeared in the August 2006 issue of the Journal of Neurology, Neurosurgery and Psychiatry.

Fluctuation in blood pressure is likely to be a significant cause of the peaks and troughs in risk, wrote Dr. Shinichi Omama and colleagues of the department of neurosurgery at Iwate. Since it is known that platelets stick together more easily in the morning and that blood tends to be thicker at this time, the researchers believe this may increase the risk of an ischemic stroke and decrease the risk of a hemorrhagic stroke in the morning; on the other hand, when blood is less thick and sticky, excessive bleeding is more likely, raising the risk of a hemorrhagic stroke.



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