The purpose of this study was to investigate the relationship between work organization factors and WRSP in a large representative sample of Korean workers. There were three key findings from this study. First, organizational factors related to violence, discrimination, work-life imbalance, job dissatisfaction, high work demands and intensity, and job insecurity were associated with an increased prevalence of WRSP even after adjusting for an array of potential confounders. Second, male gender, age group, presence of illness, and shift/night work were background risk factors associated with high WRSP prevalence. Third, the overall prevalence of WRSP was 5.1 % in this population. Although the results must be interpreted with caution because of the cross-sectional nature of the study design, the analyses of this large population-based representative survey suggest that work organization factors are important risk factors for WRSP among Korean workers.
Those who experienced sexual harassment at work had a 3.5 times higher risk of WRSP compared to those who had not experienced sexual harassment at work. Although we could not locate studies specifically focused on a relationship between sexual harassment and workers’ sleep problems, several studies have reported the relationship between sexual harassment and workers’ physical and mental health. A study on female flight attendants showed that for those who experienced sexual harassment, the risk of poor self-rated health was 2.8 times higher than for those who had not had such an experience (Ballard et al. 2006
). There are also reports that sexual harassment heightens the risk of depression, somatic symptoms, posttraumatic stress disorder (PTSD), and other medical conditions (Street et al. 2008
), which could relate to sleep problems. Sexual harassment also raises the risk of the victims’ harmful alcohol use (Gradus et al. 2008
). Given such evidence, workers who experienced sexual harassment may have an increased risk for suffering sleep problems.
This study found that the participants who perceived sex- and age-related discrimination had more than twice the risk of WRSP than those workers who did not. Discrimination is a crucial social issue not only in multiethnic nations such as the United States but also in non-multiethnic nations as well. In the United States, the occurrence of perceived discrimination over one’s lifetime is 33.5 %, but the prevalence differs greatly by racial/ethnic group; for non-Hispanic whites, it is 30.9 %, for non-Hispanic blacks, 48.9 %, and for other racial/ethnic groups, 50.2 % (Kessler et al. 1999
). The results of the 1977–1989 US Longitudinal Survey of Mature Women (n
= 1,778) indicated that perceived workplace discrimination ranged between 11.11 and 15.14 % in black women, while it ranged between 12.10 and 16.03 % in white women. Workplace discrimination was found to be one of the strongest predictors for emotional distress and functional limitation (Pavalko et al. 2003
). In the current study, the occurrence of age and sex discrimination at the workplace was 3.4 and 1.4 %, respectively, which was lower than those of studies conducted in the United States (Kessler et al. 1999
; Pavalko et al. 2003
), but the impact on sleep seems substantial. Taking these findings into consideration, workplace discrimination may have a long-lasting negative influence on sleep behavior, possibly resulting in poor mental health of affected workers.
Additionally, in this study, those who experienced violence at their work sites were twice as likely to suffer from sleep problems as those who did not. A study of Nurses’ aides revealed that those who had been exposed to threats or violence at work had a 19 % increased risk of poor sleep compared to those without such exposures (Eriksen et al. 2008
). With fear acting as a mediator, the experience of violence is known to adversely affect workers’ health both mentally and physically (Rogers and Kelloway 1997
). Even when an individual is not a direct victim of violence, being a witness to a threatening act has been reported to exert negative effects (anxiety, illness symptoms, and negative occupational outcomes) (Hall and Spector 1991
). The result of this study corresponds with the notion and that workers who are exposed to threats of violence had an equivalent risk of sleep problems as those who actually had undergone violence at work.
Work-life imbalance has become an emerging issue in Korea because of an increase in working hours (Park et al. 2010
). Work-family imbalance has been reported to be a risk factor for depression (Frone et al. 1996
), reduced well-being (Grant-Vallone and Donaldson 2001
), exhaustion (Demerouti et al. 2004
), and alcohol abuse (Wang et al. 2010
). The work-life interface has also been reported to be related to sleep. Those who had difficulties combining work and private life had increased odds for sleep disorders (men adjusted OR 1.54, 95 % CI 1.12–2.10 and women adjusted OR 1.81, 95 % CI 1.31–2.49) (Hammig and Bauer 2009
). Another study in medical residents showed that work-family conflict was associated with sleep deprivation (Geurts et al. 1999
). Our study found that work-life imbalance is related to increased sleep problems in Korean workers as well.
Job satisfaction has been consistently associated with sleep problems in earlier studies (Doi et al. 2003
; Kuppermann et al. 1995
; Nakata et al. 2004a
; Scott and Judge 2006
). The results of our study are in line with these findings. For example, Scott and Judge (2006
) reported that insomnia is positively related to job dissatisfaction and this relationship is mediated by hostility, joviality, and attentiveness in US administrative employees (Scott and Judge 2006
). Doi et al. (2003
) found that job dissatisfaction is the second major factor for poor sleep quality, which resulted in a twofold increase in the prevalence of disturbed sleep among white-collar employees in Japan (Doi et al. 2003
). Another study in Japan revealed that low job satisfaction created a significantly increased risk for insomnia including difficulty maintaining sleep (DMS) after adjusting for multiple confounding factors (Nakata et al. 2004a
). Our study, together with those from other countries, indicates that job dissatisfaction is a risk factor associated with sleep problems.
High cognitive and emotional demands, as well as high work intensity, increased the risk of sleep problems. A significant association between cognitive demands and difficulty initiating sleep (DIS) was found in male white-collar daytime workers in Japan (Nakata et al. 2004a
). Urponen et al. (1988
) also reported that mental workload was one of the most important factors that interfered with falling asleep (Urponen et al. 1988
). In terms of work intensity, there is consensus that high job demands are related to insomnia (Cahill and Landsbergis 1996
; Kalimo et al. 2000
; Pelfrene et al. 2002
). Excessive mental/cognitive demands and working too hard may disturb the ability to fall asleep, which in turn may impair the quality of sleep.
In our study, social support at work was not associated with sleep problems after adjusting for confounding factors. Although the majority of published studies (Cahill and Landsbergis 1996
; Eriksen et al. 2008
; Jansson and Linton 2006
; Kageyama et al. 1998
; Kim et al. 2011
; Nakata et al. 2001
; Nordin et al. 2005
; Pelfrene et al. 2002
; Runeson et al. 2011
) indicate that poor social support at work is related to sleep problems, some studies suggest that the statistical significance of this relationship is attenuated after controlling for confounders (Nakata et al. 2004a
). This finding may be relevant to the fact that social support often exerts a buffering effect on health outcomes and that the significant relationship disappears if controlled for related variables. However, it is important to note that social support from one’s workplace is often more protective than social support from family or friends, suggesting the importance of workplace social support (Nakata et al. 2001
A significant association between job insecurity and sleep problems was found in this study. After the 1998 financial crisis in East Asia, Korea was no exception with regard to increased job insecurity. At the time of the crisis, a large number of workers lost their jobs and since then businesses have not been active in recruiting permanent employees (preferring temporary employees), and employers are facing organizational restructuring over time. Workers who feel their jobs are insecure may succumb to sleep disorders resulting in long-term mental stress. A study of civil servants in Britain reported that male workers who experienced organizational change tended to have increased sleep problems (Ferrie et al. 1998
). Another Swedish study discovered that workers who expected that they would lose their jobs experienced sleep disturbances (Mattiasson et al. 1990
). The results of this study support the notion that job insecurity is connected to sleep problems.
The overall prevalence of WRSP in this study was 5.1 %, which was comparable to that of 8.7 % in the fourth EWCS (Table ). The sleep problems question used in both the KWCS and the EWCS was targeted specifically to work-related sleep problems. A study in Sweden (Swedish Work Environment Survey; SWES) used a similar method to define sleep disturbances as both the KWCS and EWCS and showed a strong predictability of medically certified sickness absence (Westerlund et al. 2008
). In comparison with earlier studies that defined sleep problems in general, the definition used in the KWCS, EWCS, and SWES might have a stronger predictive validity than merely asking about general sleep problems because general sleep problems may also capture problems related to or caused by non-work-related issues. However, it is also true that the significant associations found in this study are subject to the ‘triviality trap’; that is the measurement of the independent (WRSP) and dependent (organization factors) variables is conceptually overlapping and the observed associations may be spurious (Kristensen 1996
). Thus, future studies should be undertaken to validate our finding by using objective sleep measures in a prospective study design.
The analyses of underlying factors associated with WRSP revealed that men had a 1.5 times higher odds of WRSP than women (Table ). In studies investigating sex differences in sleep problems, the majority of studies discovered that sleep problems are more frequent in women than in men (Chen et al. 2005
; Kim et al. 2011
; Paparrigopoulos et al. 2010
). However, in this study, as the definition of sleep problems was ‘work-related,’ it may be that working men in Korea have more sleep problems due to work than working women do. In the EWCS, the prevalence of sleep problems in men was 8.9 %, while it was 8.5 % in women. Thus, it is likely that the higher prevalence of sleep problems in men than in women may depend on how ‘sleep problems’ are defined. As suggested in Table , the higher prevalence of WRSP in workers with illness and working the shift/night schedule is in line with previous findings, indicating that the association was in the expected direction.
Strengths and limitations of the study
The specific strengths of this study are that: (a) the sample was both nationally representative of the Korean working population and was large in size, (b) the study measured a number of work organization factors, (c) the analyses controlled for a broad array of potential confounders related to work organization and sleep problems, and d) the survey measures were collected via face-to-face interviews resulting in very little missing data. A major criticism of the methodology of the present study is that we evaluated WRSP with a single question, which prevented us from judging the severity of sleep problems and did not allow us to compare our results with other studies that used more general questions. Moreover, the definition of WRSP may include not only those with general sleep problems, that is, insomnia, poor sleep quality, and sleep loss, but also those with more specific sleep disorders, that is, sleep apnea, excessive daytime sleepiness, severe bruxism, etc. We also acknowledge other potential limitations. First, the study is cross-sectional in nature; thus, no causal interpretations can be made. However, it may be speculated that sleep problems affect the rating of work conditions; workers with sleep problems may have issues with irritability with colleagues and supervisors, an inability to concentrate at work, difficulty accomplishing assigned tasks in a timely manner, and uncertainty that they will be able to continue their employment, leading to expressions of higher work stress (Nakata et al. 2007
). Meanwhile, poor working conditions may influence sleep problems. A two-year prospective study of the effort-reward imbalance model, the job demand-control model, and insomnia revealed that those who were not insomniac at the baseline became insomniac when exposed to high overcommitment to work (OR 1.75, p
< 0.05) and high job strain (OR 1.72, p
< 0.05) (Ota et al. 2009
). Second, most of the work organization measures consisted of single item that may raise questions as to the validity and reliability of the results. However, items such as ‘job satisfaction’ are known to hold as high a reliability as multi-item scales (Wanous et al. 1997
). Third, even though we have statistically controlled for existing disorders, it is possible that those who are suffering from sleep problems may be affected by comorbid disorders.