Circadian Rhythm and Ischemic Stroke: A Hospital-based Study in Shanghai, China

INTRODUCTION: Circadian rhythm influences the clinical spectrum of stroke. Despite extensive research, studies examining the circadian influences on stroke occurrence, focusing on demographic factors and common risk factors, are limited. This study aims to examine the distribution and circadian patterns of ischemic stroke onset times and to analyze demographic factors and risk factors related to stroke timing. METHODS: Conducted at Shanghai East Hospital, an affiliated hospital of Tongji University, this study analyzed electronic medical records from 2021 and 2022, screening 1,320 patients. A total of 406 patients met the inclusion criteria: >18 years old, Chinese nationality, diagnosed with acute ischemic stroke, and without liver disease. Stroke occurrences were categorized into six time intervals for Cosinor analysis and chi-square tests. RESULTS: Among 406 patients (62.1% male, mean age 68.7 years), stroke occurrences showed a clear circadian pattern, peaking between 08:00 and 11:59 (36.2%) and occurring predominantly during daylight hours (75.9%). Cosinor analysis confirmed significant circadian rhythmicity. Hypertension (67.5%) and diabetes (33%) were not significantly associated with stroke onset timing. No significant differences in stroke timing were observed across gender or age groups. DISCUSSION: Patients with a history of previous stroke demonstrated a significant association with late afternoon onset (p = 0.038), a pattern infrequently reported in prior studies that may reflect altered vulnerability or treatment-related factors. CONCLUSION: This study demonstrates a pronounced circadian pattern in ischemic stroke, with a latemorning peak. The observed late-afternoon signal among patients with prior stroke warrants further investigation to clarify underlying mechanisms and implications for prevention strategies.