title: Diurnal variation in onset of hemorrhagic stroke is independent of risk factor status: Takashima Stroke Registry.
abstract: BACKGROUND
  We examined the circadian periodicity of hemorrhagic stroke onset to identify any existing specific pattern and its relationship with conventional stroke risk factors using 14-year stroke registration data.
  
  
  METHODS
  Data were obtained from the Takashima Stroke Registry, which covers a stable population of approx. 55,000 in Takashima County in central Japan. Out of 499 registered first-ever hemorrhagic stroke events during 1990-2003, there were 429 (186 men, 243 women) events with classifiable onset time. Hemorrhagic stroke incidence was categorized as occurring at night (midnight to 6 a.m.), morning (6 a.m. to noon), afternoon (noon to 6 p.m.) or evening (6 p.m. to midnight). The OR (with 95% CI) of having a stroke in the morning, afternoon or evening were calculated, with night serving as reference.
  
  
  RESULTS
  There was significant diurnal variation in hemorrhagic stroke incidence (p < 0.001). The proportion of hemorrhagic strokes was highest in the morning (36.1%, 95% CI: 31.7-40.8) and lowest in the night (11.9%, 95% CI: 9.1-15.3). An excess stroke incidence in the morning was observed in both genders, in subjects < 65 years and > or =65 years, and in both intracerebral hemorrhage and subarachnoid hemorrhage. A second surge was also observed during the later part of the day. The higher daytime risk persisted after adjusting for age, gender, and risk factors.
  
  
  CONCLUSIONS
  In the examination of circadian variation of hemorrhagic stroke onset, a 2-peak temporal distribution was observed, which was independent of conventional risk factors.
authors.affiliation: Department of Health Science, Shiga University of Medical Science, Shiga, Japan. turin@belle.shiga-med.ac.jp
authors.forename: Tanvir Chowdhury
authors.initials: TC
authors.lastname: Turin
authors.forename: Yoshikuni
authors.initials: Y
authors.lastname: Kita
authors.forename: Nahid
authors.initials: N
authors.lastname: Rumana
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Takashima
authors.forename: Masaharu
authors.initials: M
authors.lastname: Ichikawa
authors.forename: Hideki
authors.initials: H
authors.lastname: Sugihara
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Morita
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Hirose
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Murakami
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Miura
authors.forename: Akira
authors.initials: A
authors.lastname: Okayama
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Robert D
authors.initials: RD
authors.lastname: Abbott
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Ueshima
mesh_terms: D000367:Age Factors; D000368:Aged; D005260:Female; D006801:Humans; D015994:Incidence; D020300:Intracranial Hemorrhages / Q000453:epidemiology* / Q000401:mortality; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D017440:Photoperiod; D012042:Registries; D012307:Risk Factors; D012737:Sex Factors; D020521:Stroke / Q000453:epidemiology* / Q000401:mortality; D013345:Subarachnoid Hemorrhage / Q000453:epidemiology / Q000401:mortality; D013997:Time Factors