Investigation of the relationship between sleep problems and work injuries

BACKGROUND
Work injuries are a major problem worldwide. Approximately 360,000 fatal occupational injuries occur yearly, and more than 960,000 workers are injured daily. The worldwide estimated cost of work injuries is over US$ 400 billion a year. In Switzerland, the number of work injuries recognised by the Swiss National Accident Insurance Institution has remained stagnant at approximately 95 work injuries per 1,000 full-time employees annually, after a decrease in work injuries in the decade before. The stagnation of the decrease and the middle rank for work injury risk in the European comparison has resulted in a demand for revising prevention measures. A preliminary literature search on potentially important but disregarded causes of work injuries revealed that little is known about the personal factors influencing work injuries and that sleep problems may be a relevant but underestimated risk for work injury. Sleep problems are one of the most common health complaints with a varying prevalence of up to 40 % depending on the sleep problem type and examination method. Sleep problems may constrict the recovery function of sleep and lead to sleepiness during the day. Sleepiness may in turn reduce work performance and increase the risk of work injury. The role of sleep as a potential risk factor in injury prevention is still under debate. The strong belief and consensus among specialists that sleep problems have an impact on the incidence of work injuries has never been approached systematically and pooled quantitatively. No data from Switzerland are currently available on this topic. Furthermore, it is unclear whether sleep quality, sleep duration and daytime sleepiness influence the various types of work injuries differently. Additionally, limited and conflicting evidence is available on factors that modify the relationship between sleep problems and work injuries.
OBJECTIVES
Derived from the above knowledge gaps and research needs, the overall aims of this thesis were to (i) better understand the influence of sleep problems on work injuries, (ii) identify susceptible types of work injuries and populations most at risk and (iii) investigate whether our international findings can be verified for Switzerland.
METHODS
The research questions of this thesis were addressed in the framework of two separate study parts. First, a systematic literature review was performed consisting of a search of several databases. Original articles quantifying the relationship between sleep problems and work injuries were included up to July 7th, 2011. Pooled relative risks expressed in odds ratios (OR) and 95 % confidence intervals (CI) were calculated through random effects models. Several subgroup meta-analyses and meta-regression analyses were performed, and the population attributable risk was estimated. Second, a case-control study including 180 cases and 551 controls was conducted at the University Hospital of Basel, Switzerland, from December 1st 2009 to June 30th, 2011. Work injuries were defined according to Swiss law. Data on sleep problems were collected using the validated German versions of the Pittsburgh Sleep Quality Index (PSQI) and the Epworth Sleepiness Scale (ESS). The potential confounders considered included socioeconomic, health, lifestyle, occupational and environmental factors. Data analysis was performed in two steps; work injuries were investigated first, and then, we analysed the full case-control sample.
RESULTS
Through the systematic review, we identified 27 studies reporting 54 estimates for the relationship between sleep problems and work injuries. Meta-analysis suggested that sleep problems significantly increased the risk of suffering a work injury by 62 % (OR = 1.62, 95 % CI 1.43 – 1.84). Approximately 13 % of the work injuries were attributed to sleep problems. Subgroup meta-analysis showed that every type of sleep problem was significantly related to work injury; the highest risks were observed for taking sleep medication and breathing related sleep problems. Sleep problems tended to increase the work injury severity. Additionally, work injury risks tended to be higher in workers with more severe sleep problems. Findings from the case-control study suggested that workers with poor sleep quality had a 78 % (OR = 1.78, 95 % CI 1.01 – 3.17) higher risk of being injured at work than workers with good sleep quality. More severe sleep problems were associated with a higher work injury risk, and having sleep problems resulted in a greater history of work injuries, independent of case status. The analysis of the work injury data revealed that the work injury types most susceptible to sleep problems were falls and musculoskeletal injuries, injuries while working with or being injured by a tool or machine, and injuries while performing a side task. Sleep quality, sleep duration and daytime sleepiness were significant risk factors for at least one type of work injury. The populations identified as most at risk for sleep problem related work injuries were workers older than 30 years, sleeping 7 hours or less per night, and working 50 hours or more per week.
CONCLUSIONS AND OUTLOOK
This thesis adds further evidence that sleep problems are a considerable risk for work injuries. We not only systematically confirmed the suggested association between sleep problems and work injuries, we also quantitatively pooled the estimated risks for the first time. Furthermore, this thesis is the first comparison between international and Swiss results. Similar risks for sleep problem related work injuries were observed, and the international findings could therefore be verified for Switzerland. The socioeconomic burden of sleep problem related work injuries was estimated as considerable. Approximately CHF 290 million are spent on the consequences of sleep problem related work injuries in Switzerland every year. Up to every fifth work injury may be prevented if sleep problems are eliminated. The knowledge about the impact of sleep problems on work safety obliges responsible parties to take preventive action. This thesis adds valuable information on how to identify the risk of sleep problem related work injuries. The identification of the work injury types most susceptible to sleep problems may contribute to a better understanding of the injury causation and thus support a comprehensive recognition of injury causes. It may be useful to check workers involved in a fatigue related work incident for the sleep problems that are found to be associated with work injuries in this thesis to prevent them from similar events. Another approach may be to target sleep-related prevention measures to the population most at risk for sleep problem related work injuries identified in this thesis. Future studies on this topic should be conducted in basic research and applied science. Basic research in the field of sleep problem related work injuries needs to better characterise the mechanisms involved in the ways that sleep problems affect work injuries. For this purpose, laboratory simulations and epidemiological studies are needed. Furthermore, newly proposed analysis methods should be verified, and measures to assess which injury relevant aspects of sleep in the workplace setting need improvement. Applied science should be used to provide practical knowledge on how to protect workforces from sleep problem related work injuries. For a successful implementation of fatigue prevention measures, evidence-based information is needed along the causal chain of events potentially leading to an incident. To predict fatigue at the organisational and individual levels, behaviourally based methodologies need post-implementation research to define thresholds. The possibility for reducing the number of work injuries through sleep education needs to be evaluated for targeted injury prevention. Before launching a screening program for sleep problems, questions on feasibility or effectiveness need to be answered. Fatigue detection technologies and fatigue proofing systems need validation. Furthermore, occupational health and safety officers need to be trained in identifying fatigue-related factors that can cause injuries. In practice, many ideas on structural and behavioural strategies for work injury prevention exist. However, there are many unanswered questions about assessing fatigue management in the workplace. These questions need to be resolved before fatigue management systems can realise their full potential for contributing to injury prevention and helping to reduce the number of work injuries.