Work load and work hours in relation to disturbed sleep and fatigue in a large representative sample
Introduction
Sleep disturbances are prevalent in society [1], [2], [3], [4] and the costs are considerable [5]. The causes of disturbed sleep are varied [4], but one obvious source is the effects of working life. Thus, shift work is well established as a cause of disturbed, or rather, shortened sleep [6], [7]. Partinen et al. [8] investigated several occupational groups and found disturbed sleep to be most common among manual workers and much less so among physicians or managing directors. Geroldi et al. [9] found in a retrospective study of older individuals (above the age of 75) that former white-collar workers reported better sleep than blue-collar workers.
In what seems to be the most detailed study so far, Ribet and Derriennic [10] studied more than 21,000 subjects in France, using a sleep disturbance index and logistic regression analysis. It was found that shift work, a long working week, exposure to vibrations, and “having to hurry” appeared to be the main risk factors, controlling for age and gender. Disturbed sleep was [1], [2], [3] more frequent in women, and in higher age groups. The importance of occupational stress has also been documented in studies in which subjects have attributed their sleep disturbances to perceived causes [3], [11].
Sleepiness has been identified as one of the major risk factors behind accidents at work and elsewhere [12], [13], [14], [15], and is suspected to cost society up to US$50 billion per year [5]. The US National Transportation Safety Board estimates that 20–30% of all transportation accidents with injury are due to fatigue [16]. The most common suggested causes of sleepiness involve sleep pathology, such as narcolepsy, sleep apnea, and insomnia [4], [14], [15] but also transient sleep disturbances, such as those due to shift work [6]. With respect to shift work, a number of studies have demonstrated high levels of sleepiness during night but also during morning shifts [6]. More dramatic effects, such as the occurrence of involuntary sleep at work have been found in several questionnaire studies [14], [17], [18], [19], [20]. It has also been described in a few studies with continuous EEG recordings during work [21], [22], [23], [24], [25].
Other aspects of work than shift work do not seem to have been investigated in relation to sleepiness. Among work-related variables, stress, for example, would be expected to suppress any appearance of sleepiness during work. One might also expect overtime work to affect sleepiness, either through increasing it via disturbed sleep, or through counteracting it through stress at work.
The present study intended to analyze the relation between disturbed sleep and fatigue on the one hand and work stress, shift work, overtime work, and physical workload on the other. To make this a worthwhile approach with possibilities to generalize, we made use of data from a very large representative sample with a high response rate.
Section snippets
Material and methods
The design used was an open cohort study with repeated national cross-sectional surveys, focusing on living conditions. These cross-sectional surveys utilize data obtained from the National Survey of Living Conditions (ULF), conducted annually by Statistics Sweden. The ULF study comprises a systematic sample of the Swedish population between 16 and 84 years (corresponding to a simple random sample) [26]. The sampling is done from a register of all Swedes with 82 strata for: region (5), age
Results
The number of cases was 18,828 (32.8%) for fatigue and 7347 (12.8%) for disturbed sleep. Table 1 shows the number of individuals exposed to the different predictors.
Table 2 shows the results from the multiple logistic regression analysis. For disturbed sleep, the significant predictors became: female gender, age (reduced risk below 50 years), present illness, hectic work, physically strenuous work, and shift work.
For fatigue, the significant predictors became: female gender, age <50 years,
Discussion
Work factors were clearly related to both dependent variables. One such factor was that of hectic work. This agrees with studies attributing disturbed sleep to work stress [3], [10], [11]. High work demand is the classical work stress factor, and when combined with low decision latitude, it has been shown to be related also to cardiovascular disease [27] and absenteeism [28].
Also, high physical workload was related to both increased sleep problems and fatigue. A negative effect on sleep of
Acknowledgements
This work was supported by the Swedish Work Environment Fund and the Swedish Working Life Institute
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