Circadian Variation in the Timing of Stroke Onset

BACKGROUND AND PURPOSE: Acute myocardial infarction and sudden death display a circadian rhythm, with a higher risk between 6 AM and noon. Some reports suggest that stroke does not follow such a circadian variation and that hemorrhagic stroke occurs more often during the evening. METHODS: A meta-analysis of 31 publications reporting the circadian timing of 11,816 strokes was performed, subdividing (when possible) by the type of stroke, according to the time of onset of symptoms. When precise timing was not given, strokes were distributed evenly (that is, biasing toward the null hypothesis of lack of circadian variation). RESULTS: All subtypes of strokes displayed a significant (P<0.001) circadian variation in time of onset, whether divided into 3-, 4-, or 6-hour time periods. There was a 49% increase (95% confidence interval, 44% to 55%) in stroke of all types between 6 AM and noon (compared with expectations if no circadian variation was present), which is a 79% (95% confidence interval, 72% to 87%) increase over the normalized risk of the other 18 hours of the day. There were 29% fewer strokes between midnight and 6 AM, a 35% decrease compared with the other 18 hours of the day. All three subtypes of stroke had a significantly higher risk between 6 AM and noon (55% for 8250 ischemic strokes; 34% for 1801 hemorrhagic strokes, and 50% for 405 transient ischemic attacks). CONCLUSIONS: These data support the presence of a circadian pattern in the onset of stroke, with a significantly higher risk in the morning.