Impact of working hours on sleep and mental health

Abstract

Background

The number of hours people are required to work has a pervasive influence on both physical and mental health. Excessive working hours can also negatively affect sleep quality. The impact at work of mental health problems can have serious consequences for individuals’ as well as for organizations’ productivity.

Aims

To evaluate differences in sleep quality and anxiety and depression symptoms between longer working hours group (LWHG) and regular working hours group (RWHG). To examine factors influencing weekly working hours, sleep quality and anxiety and depressive symptoms.

Methods

Participants were divided into two groups, RWHG and LWHG, based on working hours, with a cut-off of 48 h per week. We used the Hospital Anxiety and Depression Scale (HADS) to assess anxiety and depression symptoms and the Pittsburgh Sleep Quality Index (PSQI) to measure the quality and patterns of sleep.

Results

The response rate was 23%. Among the 429 study participants, those in the LWHG group (n = 256, 53%) had significantly more depressive and anxiety symptoms and worse sleep quality than those in RWHG (n = 223, 47%). Working time was significantly positively correlated with higher corporate position and HADS scores. Moreover, HADS scores were positively correlated with PSQI scores and negatively correlated with age.

Conclusions

This study suggests that longer working hours are associated with poorer mental health status and increasing levels of anxiety and depression symptoms. There was a positive correlation between these symptoms and sleep disturbances.

Introduction

Long working hours are commonplace worldwide and have been one of the most important topics in occupational health since the late 19th century. The European Working Time Directive (Directive 2003/88/EC) established minimum general safety and health requirements for the organization of certain aspects of working time in the European Union’s 28 member states, including for the health professions. The directive states in its pre amble that ‘the improvement of workers’ safety, hygiene and health at work is an objective which should not be subordinated to purely economic consideration’. Furthermore, it stipulates that workers should have a maximum weekly working time of 48 h, including overtime. Over recent decades, significant progress has been made worldwide in establishing statutory limits on working hours. As a result, the majority of countries now have statutory limits <48 h, and around half have a 40-h limit in place [1]. Despite this, ~22% of workers worldwide are still working >48 h per week [2].

The number of hours people are required to work has a pervasive influence not only on physical health but also on mental health. Excessive weekly working time has negative effects on workers’ health, including increasing the risk of hypertension, cardiovascular disease, chronic infection, diabetes, metabolic syndrome, sleep disturb ance, anxiety and depression [1,3–6]. Additionally, excessive working time has been implicated in several sudden deaths caused by cardiovascular diseases (e.g. stroke, acute cardiac failure, myocardial infarction and aortic aneurysm rupture) in middle-aged workers. In Japan, such deaths are called karoshi, meaning ‘death from overwork’ [7]. In Japan, the number of workers suffering from cardiovascular disease, cerebrovascular disease and mental disorders due to work has increased 3-fold in the last decade [3].

Mental health problems in the workplace have serious consequences not only for the individual, but also for the productivity of the organization. In Organisation for Economic Co-operation and Development countries, mental ill-health is responsible for between one-third and half of all long-term sickness and disability in the working age population. Data show that many people with common mental health problems struggle at work. For example, 69% of people with moderate mental health problems report having difficulty with job performance, compared with 26% of those without mental health problems [8]. Sleep disturbance is associated with substantial impairment in an individual’s quality of life. Compared with good sleepers, people with persist ent sleep disturbance are more prone to accidents, have higher rates of work absenteeism, diminished job performance, decreased quality of life and increased health care use [9]. Several studies have revealed that working overtime is related to short or disturbed sleep and can correlate with reduced sleep quality in a dose-response manner [10–12].

The aim of this study was to examine the effect of longer working hours on sleep quality, anxiety and depressive symptoms in white-collar workers.

Methods

We sent an e-mail invitation to participate in this survey, with a unique hyperlink to a questionnaire, to all alumni of the Portuguese AESE-Business School. Participation in the study was voluntary and the questionnaire was confidential and anonymous. The study received ethical approval from the institutional review board. We defined long working hours as >48 working hours per week. According to this criterion, participants were divided into a regular working hours group (RWHG) and a longer working hours group (LWHG). We designed a questionnaire to collect demographic and work characteristics data and used the Hospital Anxiety and Depression Scale (HADS) to elicit anxiety and depressive symptoms [13]. HADS is a self-reported 14-item questionnaire composed of two 7-item subscales, one measuring anxiety and one depression, which are scored separately. Each item is answered on a four-point (0–3) Likert scale, so possible scores range from 0 to 21 for both anxiety and depression, with higher scores indicating a higher level of depression or anxiety. We assessed the quality and patterns of sleep using the Pittsburgh Sleep Quality Index (PSQI) [14]. This self-reported questionnaire rates sleep quality and patterns during the previous month and evaluates seven components of sleep: subjective quality, latency, duration, usual efficiency, sleep disturbances, medication use and daytime dysfunction. A score >5 is suggestive of a sleep disorder.

Standard descriptive summary statistics were used to characterize the full sample and the two groups. Associations between variables were evaluated using the χ² test (categorical variables) and the independent t-test with unequal variances and estimated degrees of freedom (continuous variables). Regression analysis was performed on average work hours per week, PQSI and HADS scores, social and demographic variables, working habits and sleep patterns. The backward selection method using the Akaike Information Criterion was used for model selection. All analyses were performed using commercially available and open source statistical software (IBM SPSS 22.0, R 3.2.4). In all regressional analysis, the symmetry of residuals and large sample size guaranteed estimates’ quality. A P value <0.05 was considered significant.

Results

Surveys were sent to 2059 alumni and 479 completed surveys (23%) were returned and validated. The responders were divided into RWHG (n = 223, 47%) and LWHG (256, 53%). The average weekly working hours were 38 (SD 11.8) in RWHG and 55 (SD 6.5) in LWHG. In addition, a larger proportion of the LWHG reported working >5 days per week (32 versus 7%). Characteristics of the study participants are shown in Table 1. In both groups, participants were mostly married men with children. The propensity to work long hours was associated with level in the corporate hierarchy. Interestingly, LWHG members had higher level corporate positions than RWHG subjects. This means that those with higher level corporate positions were statistically significantly more likely to work more weekly hours than participants with lower positions. Moreover, LWHG subjects were more likely to take work home (75%) than those in the RWHG (55%; P < 0.001). We found no significant differences in shift work between the two groups.

An independence test to rule out any confounding between sex and job level, using the χ² statistic, yielded P >0.99. A similar test was performed for sex and having children, with P = 0.83. Both of these factors can be considered independent of sex.

Data on PSQI and HADS scores are reported in Table 2. The RWHG had significantly more sleeping time (mean 6.7 h, SD 0.8) than the LWHG (mean 6.4 h, SD 0.9; P < 0.001), so sleeping hours were significantly negatively associated with weekly working hours (P < 0.05). As shown in Table 2, PSQI scores were not significantly higher for those in LWHG. Nonetheless, using a cut-off score of 5 on the PSQI scale, a significantly higher number of subjects in LWHG (66%) reported more sleep disorders than in the RWHG (54%). In addition, there were significantly higher total HADS scores and HADS subscale scores for anxiety and depression in LWHG members compared with those in RWHG. Although HADS scores do not provide definitive diagnoses of anxiety and depressive disorders, these results show that LWHG members reported significantly more anxiety and depression symptoms than those in RWHG.

Results of the regression analysis are shown in Tables 3–5.

As shown in Table 3, a significant positive relationship was found between working hours per week and work in some professional areas, having a higher level of corpor ate responsibility, taking work home and the number of working days per week. Additionally, a negative correlation was found between working hours per week and the number of vacation days annually.

The results from the regression analysis for PSQI scores (Table 4) suggested a positive correlation between PSQI scores and both HADS-depression and HADS-anxiety subscale scores.

There were positive correlations between the total HADS score and both PSQI score and taking work home. In addition, there was a negative correlation between the HADS total score and age.

Discussion

Our study found significantly higher anxiety and depression symptom scores in respondents reporting long working hours compared with those reporting regular hours. These findings are similar to those of several previous studies [7,15–17]. Moreover, there was a significant negative correlation between total HADS score and age. This relationship can probably be explained by burnout, since age has been found to be related to burnout. For instance, in younger employees, the level of burnout is higher than in those over 30 or 40 years old [18], suggesting that burnout appears early in a person’s career and may be a risk factor for developing depression [19]. However, the apparent relationship between burnout and age is inconsistent and further studies are needed to clarify this [20].

There is general agreement that long hours of work adversely affect sleep [21]. In our study, there were more participants reporting sleep disturbance in the LWHG than the RWHG, which is compatible with previous observations [12,22]. Additionally, our results showed a significant inverse relationship between working time and sleep duration. Inadequate recovery because of sleep deprivation is considered an important component of the pathway from long work hours to increased fatigue and risk of health problems [23,24]. Moreover, shift work is associated with sleep disturbance [1,21,25], which may bias the results. However, there were only seven shift workers in the RWHG (3%) and 12 in the LWHG (5%), a non-significant difference unlikely to have biased the results. Sleep problems may be associated with psychiatric conditions. Thus, there is growing experimental evidence that the relationship between psychiatric disorders and sleep is complex and includes bi-directional causation [26]. The positive correlation between PSQI scores and HADS-anxiety and HADS-depression scores seem to support this relationship. In other words, our results showed an association between poor sleep quality and anxiety and depression symptoms.

A sex-specific difference was also found between the two groups, with more men in the LWHG (73%) than the RWHG (62%). Similar results were obtained in a large survey regarding working conditions in the European Union [27]. Women tend to work shorter hours than men, presumably because they still retain primary responsibility for the majority of housework and childcare. Not surprisingly, LWHG members had significantly less vacation time, worked more days per week and took more work home than RWHG members.

Our study has several limitations. Firstly, it was a cross-sectional study, whereas longitudinal research would be necessary to clarify the long-term effects of long working hours on mental health and sleep quality. Secondly, long working hours may in part affect mental health through factors not measured in our study, such as work–family conflicts [28], burnout [18], a prolonged increase in cortisol levels [28,29] and alcohol abuse [30]. Finally, the participants in the study were alumni from a business school, so the results may not be applicable to other workers. In particular, the participants were white-collar workers and with a higher level of education than the general population.

Almost a century has passed since the 1919 adoption of the first international labour standard on working hours, which established the principle of the 8-h working day and 48-h working week. Despite progress in legislation, ~22% of workers worldwide still work >48 h per week [2]. Surprisingly, 53% of workers in our study reported working >48 h per week, suggesting that the European Working Time Directive has been ineffective, at least at higher corporate levels.

Work is important for economic self-sufficiency and a meaningful way of living. However, as demonstrated in this study, long working hours can also be associated with problems such as an increased risk of sleep disturbance and symptoms of anxiety and depression. Our findings suggest that we still need to advocate shorter working hours in order to preserve health and well-being.

Conflicts of interest

None declared.

References

Author notes