Background and purpose: The study purpose was to identify patterns of variation in stroke incidence among days of the week and examine if it is modified by conventional stroke risk factors: hypertension, diabetes, drinking and smoking.
Methods: Data were obtained from the Takashima Stroke Registry, which covers a stable population of roughly 55,000 residents of Takashima County in central Japan. A total of 1,773 stroke cases (men: 943 and women: 830) occurred between 1988 and 2003. We divided the days into 3 groups: 'weekend', 'after weekend' and 'rest of the week', and calculated stroke incidence rates and incidence rate ratios. To identify the effect of conventional risk factors on the variation, proportion of differences between observed and expected stroke incidences were considered.
Results: The stroke incidence for the after weekend group (250.1 per 100,000 person years, 95% CI: 222.0-278.3) was higher than for the other day groups among men. The after weekend increase was observed mainly among older men aged 65 years or more. Among the stroke subtypes, the incidence for cerebral infarction was highest in the after weekend group (857.2, 95% CI: 730.6-983.8) and was 1.37 times (95% CI: 1.12-1.68) higher than in the rest of the week group. Tendency of after weekend increase was observed regardless of the presence or absence of risk factor history.
Conclusions: Week day variation for stroke was observed predominantly among older men regardless of presence and absence of risk factor history. Information about the weekly trend regarding episode of increased stroke incidence can be used as a surrogate predictor for stroke onset and would be helpful in designing more effective insights for preventive strategies.