FRIDAY, Aug. 18, 2006 (HealthDay News) -- Strokes may be timed to the body's internal clock, Japanese researchers say.
Researchers at Iwate Medical University analyzed data from 13,000 patients who had one of three types of stroke -- cerebral infarction, subarachnoid hemorrhage, intracerebral hemorrhage -- for the first time.
All three kinds of strokes had two periods of peak occurrence: one between 6 a.m. and 8 a.m. and another between 6 p.m. and 8 p.m. Stroke occurrence declined significantly during sleep.
Upon closer analysis, the researchers did find that cerebral infarction -- where blood flow to the brain is restricted -- had a higher peak in the morning and a lower peak in the afternoon than the other two kinds of stroke, which were more likely to have lower peaks in the morning and higher peaks in the afternoon.
About 20 percent of cerebral infarction occurred during sleep, with most of them concentrated in the time immediately before waking up, although it's likely the stroke would have actually begun earlier, the study authors said.
The findings were published in the Aug. 17 online edition of the Journal of Neurology, Neurosurgery and Psychiatry.
The U.S. National Institute of Neurological Disorders and Stroke has more about stroke.