Circadian rhythm types and sleep health in college students: Insights from 24-hour heart rate variability monitoring

Abstract

Circadian rhythm (CR) disruptions are prevalent among college students; however, systematic investigations of autonomic nervous system (ANS) dynamics across distinct CR types remain limited. This study employed a multimodal framework integrating actigraphy and self-reported activity logs to classify 145 college students into three CR types: entrained, delayed, and fragmented. We analyzed 24-hour heart rate variability (HRV) patterns, focusing on high-frequency (HF), low-frequency (LF), and the LF/HF ratio across 288 time slots within a single CR cycle. Non-parametric statistical analyses with Benjamini–Hochberg correction were applied to assess group differences. Results revealed distinct ANS profiles associated with CR stability. The entrained group exhibited robust circadian HRV oscillations, characterized by nocturnal parasympathetic dominance and clear day-night transitions in HF. In contrast, the fragmented group displayed globally suppressed HF, elevated LF/HF ratios, and attenuated circadian rhythmicity, indicative of chronic sympathetic dominance and impaired parasympathetic recovery. The delayed group retained circadian ANS rhythmicity but exhibited a 2–3 h phase delay in nocturnal HF peaks, reflecting misalignment with socially imposed schedules. Temporal analyses of 12-hour HF-defined epochs further demonstrated that only the entrained group exhibited structured transitions between consolidated nocturnal sleep and clustered daytime activity, a pattern absent in fragmented and delayed types. These findings underscore the critical role of CR stability in maintaining ANS equilibrium and sleep health. Targeted interventions that address CR-specific autonomic dysregulation – such as enhancing parasympathetic activity in fragmented type and gradual phase realignment in delayed type – may help mitigate the adverse consequences of circadian misalignment in college populations.