Correlation between sunrise/sunset times and peak onset periods of primary intracerebral hemorrhage

Although the bimodal diurnal pattern of intracerebral hemorrhage (ICH) onset has been well established, the exact timing of these peaks remains inconsistent across previous studies. Sunrise and sunset times serve as critical zeitgebers closely tied to diurnal rhythms, but whether their geographical and seasonal variations can explain the observed differences in peak timing remains unknown. This study aimed to investigate potential correlations between sunrise/sunset times and morning/afternoon onset peaks of ICH. In this retrospective cross-sectional study, we categorized data by hemorrhage location and seasonal onset. Primary analysis examined monthly variations in morning/afternoon peaks relative to corresponding sunrise/sunset time fluctuations, with partial correlation analysis controlling for confounders to refine associations. The study included 11,946 patients with first-ever primary ICH. These findings revealed that morning peaks commenced before sunrise, peaked at sunrise, while afternoon peaks peaked before sunset and concluded at sunset. Significant correlations were observed exclusively in the Deep ICH group, with morning peak times showing association with sunrise (partial r = 0.85, p = 0.002) and afternoon peak times with sunset (partial r = 0.69, p = 0.025). No other correlations reached significance. Our study found that sunrise/sunset times showed significant correlations with morning/afternoon onset peaks of ICH exclusively in Deep ICH cases. When addressing peak onset periods in Deep ICH, regional and seasonal variations in daylight hours should be considered.