Morning surge in circadian periodicity of ischaemic stroke is independent of conventional risk factor status: findings from the Takashima Stroke Registry 1990–2003.

Background: We examined the circadian periodicity of ischaemic stroke (IS) onset and its relationship with conventional risk factors using 14-year stroke registration data. Methods: Ischaemic stroke event data were acquired from the Takashima Stroke Registry, which covers a stable population of ≈55 000 in Takashima County in central Japan. During 1990–2003 there were 637 (353 men and 284 women) cases with classifiable onset time. IS incidence was categorized as occurring at night (midnight to 6 am), morning (6 am to noon), afternoon (noon to 6 pm), and evening (6 pm to midnight). The OR (with 95% CI) of having an IS in the morning, afternoon, and evening were calculated, with night serving as reference. Results: There was significant diurnal variation in IS incidence ( P < 0.001). The proportion of events was highest in the morning (40.7; 95% CI: 36.9–44.5), and lowest in the night (14.0; 95% CI: 11.5–16.9). In the morning an excess incidence of IS was observed in both genders, in subjects <65 years and ≥65 years, and in all IS subtypes. The morning excess of IS incidence was similar across seasons and days of the week. For all IS, morning excess was higher (odds ratio: 2.91; 95% CI: 2.29–3.70) compared to the night period. Similar trends persisted after adjusting for age, gender, and risk factors. Conclusion: In the examination of circadian variation of IS onset, a predominant morning peak independent of conventional risk factors was observed in a Japanese population with similar pattern across seasons of the year and days of the week. [ABSTRACT FROM AUTHOR]