Original articleEffort–reward imbalance at work and risk of sleep disturbances. Cross-sectional and prospective results from the Danish Work Environment Cohort Study☆
Introduction
Sleep disturbances are associated with a wide range of health problems and diseases. People suffering from sleep disturbances have lower self-rated health, report more physical and mental health complains, and have more sickness absence [1], [2], [3]. Moreover, a meta-analysis of 10 case–control and cohort studies revealed that sleep disturbance was a risk factor for incident coronary heart disease (CHD) [4]. Other studies have shown that sleep disturbances were prospectively associated with the incidence of diabetes [5], [6], obesity [7], and depression [8]. An experimental study demonstrated that restricting participants to 4 hours sleep per night over a period of 6 days resulted into decreased glucose tolerance, an increase in cortisol concentration, and heightened activity of the sympathetic nervous system [9].
The contribution of working conditions to sleep disturbances has been investigated in numerous studies (for an extensive review, see Ref. [1]). In particular, shift work and nonstandard working hours have been identified as important risk factors [1], [10], [11], [12]. Sleep disturbances were also associated with adverse psychosocial working conditions, such as high quantitative workload, low decision latitude, or role conflicts [1], [13], [14], [15], [16], [17], [18]. However, with a few exceptions [17], [18], the vast majority of research studies on psychosocial working conditions and sleep are cross-sectional in design and, therefore, limited in drawing causal inference.
In recent years, the model of effort–reward imbalance (ERI) at work has emerged as a new theoretical approach for conceptualizing health-hazardous psychosocial working conditions. The model posits that a “high cost/low gain” situation at work, in which individuals spent high effort while receiving low rewards (in terms of monetary gratification, career opportunities, esteem, respect, and job security), elicits severe psychological distress, which consequently affects both mental and physical health. It is further assumed that ERI has, in particular, adverse health consequences, when it co-occurs with a motivational disposition called “work-related overcommitment” [19], [20]. The ERI model has been tested foremost with regard to cardiovascular disease [21], [22] but has recently also been used in research on other health outcomes [23], [24], [25], [26]. Cross-sectional multivariate analyses revealed a statistically significant association between ERI and sleep disturbances in two Japanese studies and one Swedish study [27], [28], [29], whereas a study in Germany did not find a statistically significant relation in the final multivariate model [30].
To our knowledge, the impact of ERI on sleep disturbances has not been analyzed in a prospective study or within a national workforce yet. This article aims to fill this research gap by studying ERI and risk of sleep disturbances in a 5-year follow-up analysis of a representative sample of the Danish workforce.
Section snippets
Study design and population
The Danish Work Environment Cohort Study (DWECS) was established in 1990 and is a longitudinal study to assess sociodemographic factors, work environment characteristics, health behaviors, and health status in the Danish working population [31]. In the DWECS 2000 survey, 11,437 randomly selected Danish residents were approached, of whom 8583 participated in the survey (response rate: 75%). Data were collected by means of telephone interviews. Among the respondents, 5292 were gainfully employed
Study population characteristics and cross-sectional association with prevalence of sleep disturbances at baseline
Table 2 shows the characteristics of the study population and baseline associations with prevalence of sleep disturbances. Among the 2614 respondents, 1318 were women (50.4%) and mean age was 40 years (S.D.=9 years). The majority of the participants were white collar workers (72%), and most worked during daytime (83%).
At baseline, 263 (10.1%) participants reported sleep disturbances. When all variables were adjusted for each other, female gender, reduced self-rated health, high number of
Discussion
ERI was cross-sectionally associated with prevalence of sleep disturbances in both men and women after adjustment for numerous covariates in this representative sample of the Danish workforce. When associations were analyzed prospectively, we found for men that the highest ERI quartile predicted a twofold increased risk of incident sleep disturbances and that the continuous ERI ratio at baseline was significantly associated with sleep disturbance score at follow-up. Among women, ERI was not
Acknowledgments
This study was, in part, conducted as a project for obtaining a Bachelor of Science degree in Public Health at the University of Copenhagen by two of the authors (M.N. and T.S.S.). Data analyses were conducted at the National Research Centre for the Working Environment, Denmark, and were partly funded by a grant (5-2006-04) from the Danish Working Environment Research Fund. We thank Jakob B. Bjørner, PhD, for his insightful comments on an earlier draft of this article and Dorthe Johansen, BSc,
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The study was conducted at the National Research Centre for the Working Environment, Copenhagen, Denmark.