Stress and Health 27: e71–e82 (2011) © 2010 John Wiley & Sons, Ltd. e71 RESEARCH ARTICLE Work Stressors and Impaired Sleep: Rumination as a Mediator Martial Berset* † , Achim Elfering, Stefan Lüthy, Simon Lüthi & Norbert K. Semmer Department of Psychology, University of Bern, Bern, Switzerland Abstract An association between stress at work and impaired sleep is theoretically plausible and supported by empirical evidence. The current study’s main aim was to investigate how the influence of stressors is carried over into the evening and the night. We assume that this relationship is mediated by perseverative cognitions. We tested this assumption in two cross-sectional samples with structural equation modeling, using bootstrapped standard errors to test for significance. Effort–reward imbalance and time pressure were used as stressors, and rumination as a measure for perseverative cognitions. Results show that the stressors are related to perseverative cognitions, and these are related to impaired sleep in both samples. Indirect effects are significant in both samples. With rumination controlled, direct effects of stressors on sleep are only significant in one out of four cases. Thus, there is full media- tion in three out of four cases, and partial mediation in the fourth one. Our results underscore the notion that perseverative cognitions are crucial for transferring negative effects of work stressors into private life, including sleep, thus hindering individuals to successfully recover. Copyright © 2010 John Wiley & Sons, Ltd. Received 7 December 2009; Revised 20 March 2010; Accepted 2 June 2010 Keywords stress; work; sleep; rumination; effort–reward imbalance; time pressure *Correspondence Martial Berset, Department of Psychology, University of Bern, Muesmattstrasse 45, CH – 3000 Bern 9, Switzerland. † Email: martial.berset@psy.unibe.ch Published online 9 July 2010 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/smi.1337 Introduction The assumption that stress at work can lead to impaired sleep quality seems plausible, and empirical evidence supports this association (cf. Åkerstedt, 2006). In this study, we want to confirm these findings, and to inves- tigate potential mediating processes. Specifically, we assume that the association between work stress and impaired sleep is mediated by perseverative cognitions (i.e. rumination). We tested this mediation hypothesis using structural equation modeling in two cross- sectional samples. Stress at work has been shown to be detrimental for an individual’s health (cf. Sonnentag & Frese, 2003). However, based on the allostatic load (McEwen, 1998) and the effort–recovery model (Meijman & Mulder, 1998), Geurts and Sonnentag (2006) highlighted the crucial role of successful recovery during evenings, weekends and vacations for the prevention of these det- rimental effects on health. Recovery is regarded as a process of psychophysiological unwinding during which depleted resources can replenish. If this replen- ishment cannot be achieved, individuals have to com- pensate their reduced resources with more effort in order to maintain performance at work. As a conse- quence of this compensatory effort, the need for recov- ery increases, and a recovery debt develops. Unless