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

We examined the circadian periodicity of ischaemic stroke (IS) onset and its relationship with conventional risk factors using 14-year stroke registration data. Ischaemic stroke event data were acquired from the Takashima Stroke Registry, which covers a stable population of approximate to 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. 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. 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.