The Role of Rumination and Worry in the Bidirectional Relationship Between Stress and Sleep Quality in Students

Poor sleep is strongly associated with stress; however, the mediators of this relationship are not well understood. Cognitive arousal in the form of rumination and worry may mediate this relationship, but previous studies have primarily focused on patients with insomnia or employed cross-sectional designs. This study aimed to explore the causal relationship between sleep quality and stress using two-wave longitudinal data and examining the theoretical assumptions of insomnia models in a healthy, non-clinical student population. Research was conducted using a paper-and-pencil method. The sample included 302 undergraduate students from the University of Zagreb. Most of the participants were female (79.8%) and aged between 18 and 33 years, representing various fields of study. The research problem was examined through multiple mediation analysis. The results confirm our initial hypothesis regarding the bidirectional relationship between stress and sleep quality, which is partially mediated by rumination. The mediating effect of worry is significant only in parallel mediation; poor sleep quality leads to increased rumination ( p < 0.01), which in turn predicts more worry ( p < 0.01), and greater worry predicts more stress ( p < 0.01). The effect sizes indicate that stress has a more significant impact on sleep problems ( β = 0.345, p < 0.01) than sleep problems have on stress ( β = 0.203, p < 0.01). These findings are important for planning preventive activities and therapeutic interventions.