Temporal patterns of stroke onset. The Framingham Study.

BACKGROUND AND PURPOSE Several studies have shown stroke onset to vary by season, day of the week, and time of day. These temporal patterns, which may provide insights into pathogenesis, were found mainly in clinical series, which can be subject to selection bias. To obtain a less distorted picture of stroke onset, we examined the month and season, day of the week, time, and place stroke occurred in a community-based cohort. METHODS Over a 40-year period of surveillance of the Framingham Study cohort of 5070 people aged 30 to 62 years and free of stroke and cardiovascular disease at entry, 637 completed initial strokes occurred. Month, season, day of the week, time of day, and place of occurrence of stroke were ascertained systematically and related prospectively to stroke incidence, subtype, and gender. RESULTS Winter was the peak season for cerebral embolic strokes. Significantly more stroke events occurred on Mondays than any other day, particularly for working men. For intracerebral hemorrhages, a third happened on Mondays in both genders. The time of day when strokes most frequently occurred was between 8 AM and noon. This pattern was true for all stroke subtypes. This pattern persisted when individuals whose onset occurred while sleeping or on awakening were excluded. Stroke in general occurred more at home, with hemorrhagic strokes occurring outside the home and cerebral embolisms in the hospital more than other subtypes. CONCLUSIONS Temporal patterns of stroke onset were observed for season, day of the week, time of day, and place in a community-based population. These findings suggest that there are periods of increased risk of stroke that may be amenable to preventive strategies.