Introduction: Aging and the Multifaceted Influences on Adaptation to Working Time

This special issue of Chronobiology International presents a selection of papers originally delivered at the 18th International Symposium on Shift Work and Working Time, held at Yeppoon, Australia, in August 2007. The key theme of the symposium was “Aging and Working Time: Creating Safe Environments.” Older workers are widely believed to experience greater difficulty than younger workers adapting to shift work and irregular work schedules. However, while the three reviews of age effects published here (Costa & Di Milia, ; Folkard, ; Gander & Signal, ) identify evidence that older workers do indeed adapt less well, they also demonstrate that much more research is urgently required. The remaining papers address various aspects of the impact of work schedules on health, safety, sleep, and performance. They can be divided into three broad categories: circadian and other periodic factors; sleep, sleepiness, and fatigue; and other aspects of health and adjustment. This collection of papers showcases the best of contemporary research on the safety and health effects of working hours, continuing the tradition established by the two previous issues of the journal devoted to earlier symposia on shift work and working time.     

Diurnal urinary 6-sulfatoxymelatonin levels among healthy Danish nurses during work and leisure time

The present study aims to examine the influence of evening and night shift work, compared to day shift work, on melatonin secretion in nurses in a field setting. Effects were examined during a workday and during a day off. Both fixed schedules and mixed or rotating schedules were studied. In total, 170 nurses were studied: 89 nurses worked fixed schedules, 27 nurses worked the day shift, 12 nurses worked the evening shift, 50 nurses worked the night shift, and 82 nurses worked mixed schedules, with data collected during a day (n=17), evening (n=14), or night shift (n=50). All spot urine samples were collected during 24 h from the participants on a work day and on a day off and were analyzed for 6-sulphatoxymelatonin. On the day of urine sampling, participants filled in the Karolinska Sleep Diary. Additional information was collected through a telephone interview. Data were analyzed using a mixed procedure with autoregressive covariance structure. The present study showed that shift work affected the concentrations of 6-sulphatoxymelatonin in the short term by lower excretion in urine from nurses working the night compared to day shift on a workday and on a day off as well. No significant differences were observed between a workday and a day off when doing day and evening shifts, irrespective of mixed and fixed schedules. Sleep length was reduced workdays (from 6.1-6.8 h) among all nurses, compared to days off (from 7.8-8.7 h).     

Diurnal Urinary 6‐Sulfatoxymelatonin Levels among Healthy Danish Nurses during Work and Leisure Time

The present study aims to examine the influence of evening and night shift work, compared to day shift work, on melatonin secretion in nurses in a field setting. Effects were examined during a workday and during a day off. Both fixed schedules and mixed or rotating schedules were studied. In total, 170 nurses were studied: 89 nurses worked fixed schedules, 27 nurses worked the day shift, 12 nurses worked the evening shift, 50 nurses worked the night shift, and 82 nurses worked mixed schedules, with data collected during a day (n=17), evening (n=14), or night shift (n=50). All spot urine samples were collected during 24 h from the participants on a work day and on a day off and were analyzed for 6‐sulphatoxymelatonin. On the day of urine sampling, participants filled in the Karolinska Sleep Diary. Additional information was collected through a telephone interview. Data were analyzed using a mixed procedure with autoregressive covariance structure. The present study showed that shift work affected the concentrations of 6‐sulphatoxymelatonin in the short term by lower excretion in urine from nurses working the night compared to day shift on a workday and on a day off as well. No significant differences were observed between a workday and a day off when doing day and evening shifts, irrespective of mixed and fixed schedules. Sleep length was reduced workdays (from 6.1–6.8 h) among all nurses, compared to days off (from 7.8–8.7 h).     

Flexible Working Hours,Health, and Well-Being in Europe: Some Considerations from a SALTSA Project

The project brought together researchers from 9 EU-Countries and resulted in a number of actions, in particular the following: (a) There is an urgent need of defining the concept of flexible working hours, since it has been used in many different and even counterintuitive ways; the most obvious distinction is where the influence over the working hours lies, that is between the “company-based flexibility” and the “individual-oriented flexibility”; (b) The review of the Legislation in force in the 15 European countries shows that the regulation of working times is quite extensive and covers (Council Directive 93/104/EC) almost all the various arrangements of working hours (i.e., part-time, overtime, shift, and night work), but fails to provide for flexibility; (c) According to the data of the Third EU Survey on Working Conditions, longer and “irregular” working hours are in general linked to lower levels of health and well-being; moreover, low (individual) flexibility and high variability of working hours (i.e., company-based flexibility) were consistently associated with poor health and well-being, while low variability combined with high autonomy showed positive effects; (d) Six substudies from different countries demonstrated that flexible working hours vary according to country, economic sector, social status, and gender; overtime is the most frequent form of company-based flexibility but has negative effects on stress, sleep, and social and mental health; individual flexibility alleviates the negative effects of the company-based flexibility on subjective health, safety, and social well-being; (e) The literature review was able to list more than 1,000 references, but it was striking that most of these documents were mainly argumentative with very little empirical data. Thus, one may conclude that there is a large-scale intervention ongoing in our society with almost completely unknown and uncontrolled effects. Consequently, there is a strong need for systematic research and well-controlled actions in order to examine in detail what flexible working hours are considered, what and where are their positive effects, in particular, as concerns autonomy, and what regulation seem most reasonable.     

The 24-hour society between myth and reality

The 24-hour society appears to be an ineluctable process towards a social organisation where time constraints are no more "restricting" the human life. But, what kind of 24-hour society do we need? At what costs? Are they acceptable/sustainable? Shift work, night work, irregular and flexible working hours, together with new technologies, are the milestone of this epochal passage, of which shift workers are builders and victims at the same time. The borders between working and social times are no more fixed and rigidly determined: not only the link between work place and working hours is broken, but also the value of working time changes according to the different economic/productive/social effects it can make. What are the advantages and disadvantages for the individual, the companies, and the society? What is the cost/benefit ratio in terms of physical health; psychological well-being, family and social life? The research on irregular working hours and health shows us what can be the negative consequences of non-human-centered working times organisations. Coping properly with this process means avoiding a passive acceptance of it with consequent maladjustments at both individual and social level, but adopting effective preventive and compensative strategies aimed at building a more sustainable society, at acceptable costs and with the highest possible benefits.     

The interference of flexible working times with the circadian temperature rhythm--a predictor of impairment to health and well-being?

In order to analyze whether impairments to health and well-being under flexible working hours can be predicted from specific characteristics of the work schedules, periodic components in flexible working hours and their interference with the circadian temperature rhythm were analyzed applying univariate and bivariate spectrum analyses to both time series. The resulting indicators of spectral power and phase shift of these components were then related to reported health impairments using regression analysis. The results show that a suppression of both the 24 and the 168 h components in the work schedules (i.e., a lack of periodicity) can be used to predict reported health impairments, and that if there are relatively strong 24 and 168 h components left in the work schedules, their phase difference with the temperature rhythm (as an indicator of the interference between working time and the circadian rhythm) further predicts impairment. The results indicate that the periodicity of working hours and the amount of (circadian) desynchronization induced by flexible work schedules can be used for predicting the impairing effects of flexible work schedules on health and well-being. The results can thus be used for evaluating and designing flexible shift rosters.     

Work Ability of Health Care Shift Workers: What Matters?

This paper aims at identifying variables associated with inadequate work ability among nursing personnel at a public hospital, considering factors related to socio‐demographic, lifestyles, working conditions, and health outcomes. A cross‐sectional study was conducted in a university hospital in São Paulo, Brazil, as part of a larger research study on tolerance to 12 h night work. Nursing staff included registered nurses, nurse technicians, and nurse aides; in total, there were 996 healthcare workers (878 female; 118 male) at the time of the study. Some 696 workers (69.9%) of the population agreed to participate. Data collection (October 2004–July 2005) was based on a comprehensive questionnaire about living and working conditions (including incivility at work, work demands, work control, and support), mental and physical health symptoms (fatigue and sleep problems), and work ability. This report presents analyses of the adapted Brazilian version of the Work Ability Index (WAI) and associated variables. The study population worked one of the following shift schedules at this hospital: 12 h nights followed by 36 h off or 9 h or 6 h day (morning or afternoon) shifts. The mean age of the respondents was 34.9 (S.D.±10.4) years of age; 31.5% of the participants held two jobs. Statistical analyses using a hierarchical multiple logistic regression model were performed to evaluate the factors associated with inadequate (moderate and low scores) of the WAI. The significantly associated factors were socio‐demographic (income responsibility, sole breadwinner, raising kids, age group), working conditions (thermal discomfort, organization of the workplace, and verbal abuse), and health outcomes (high body mass index, obesity, sleep problems, and fatigue). In spite of limitations of the study design, results indicate that the nursing profession is associated with stressful working conditions, contributing to inadequate WAI. This is in addition to bad living conditions and precarious work. Intervention measures, either at the workplace or at individual levels, are necessary to prevent a decrease in work ability, even in this quite young working population.     

Flexible working hours, health, and well-being in Europe: some considerations from a SALTSA project

The project brought together researchers from 9 EU-Countries and resulted in a number of actions, in particular the following: (a) There is an urgent need of defining the concept of flexible working hours, since it has been used in many different and even counterintuitive ways; the most obvious distinction is where the influence over the working hours lies, that is between the “company-based flexibility” and the “individual-oriented flexibility”; (b) The review of the Legislation in force in the 15 European countries shows that the regulation of working times is quite extensive and covers (Council Directive 93/104/EC) almost all the various arrangements of working hours (i.e., part-time, overtime, shift, and night work), but fails to provide for flexibility; (c) According to the data of the Third EU Survey on Working Conditions, longer and “irregular” working hours are in general linked to lower levels of health and well-being; moreover, low (individual) flexibility and high variability of working hours (i.e., company-based flexibility) were consistently associated with poor health and well-being, while low variability combined with high autonomy showed positive effects; (d) Six substudies from different countries demonstrated that flexible working hours vary according to country, economic sector, social status, and gender; overtime is the most frequent form of company-based flexibility but has negative effects on stress, sleep, and social and mental health; individual flexibility alleviates the negative effects of the company-based flexibility on subjective health, safety, and social well-being; (e) The literature review was able to list more than 1,000 references, but it was striking that most of these documents were mainly argumentative with very little empirical data. Thus, one may conclude that there is a large-scale intervention ongoing in our society with almost completely unknown and uncontrolled effects. Consequently, there is a strong need for systematic research and well-controlled actions in order to examine in detail what flexible working hours are considered, what and where are their positive effects, in particular, as concerns autonomy, and what regulation seem most reasonable.     

Payroll data based description of working hours in the Danish regions

ABSTRACT

The aim was to describe the organization of working hours in the Danish regions according to sex, age and calendar year. Based on the Danish Working Hour Database (DWHD), individuals were classified according to schedules: Permanent day (57.8%), evening (1.7%), or night (1.2%); day/evening (22.0%); day/night (6.6%); evening/night (0.6%); and day/evening/night (10.2%). More men (9.1%) than women (5.9%) worked day/night, whereas more women (10.9%) than men (7.4%) worked day/evening/night. More young than older employees worked day/evening/night, and fewer worked permanent day or night. From 2008 to 2015 we observed a trend towards more employees working permanent day and fewer employees working other schedules. Altogether DWHD provides a strong tool in research on working hours.     

Factors Associated With Shift Work Disorder in Nurses Working With Rapid-Rotation Schedules in Japan: The Nurses’ Sleep Health Project

Workers who meet the criteria for shift work disorder (SWD) have elevated levels of risk for various health and behavioral problems. However, the impact of having SWD on shiftworkers engaged in rapid-rotation schedules is unknown. Moreover, the risk factors for the occurrence of SWD remain unclear. To clarify these issues, we conducted a questionnaire-based, cross-sectional survey on a sample of shiftworking nurses. Responses were obtained from 1202 nurses working at university hospitals in Tokyo, Japan, including 727 two-shift workers and 315 three-shift workers. The questionnaire included items relevant to age, gender, family structure, work environment, health-related quality of life (QOL), diurnal type, depressive symptoms, and SWD. Participants who reported insomnia and/or excessive sleepiness for at least 1 mo that was subjectively relevant to their shiftwork schedules were categorized as having SWD. The prevalence of SWD in the sampled shiftworking nurses was 24.4%; shiftworking nurses with SWD showed lower health-related QOL and more severe depressive symptoms, with greater rates of both actual accidents/errors and near misses, than those without SWD. The results of logistic regression analyses showed that more time spent working at night, frequent missing of nap opportunities during night work, and having an eveningness-oriented chronotype were significantly associated with SWD. The present study indicated that SWD might be associated with reduced health-related QOL and decreased work performance in shiftworking nurses on rapid-rotation schedules. The results also suggested that missing napping opportunities during night work, long nighttime working hours, and the delay of circadian rhythms are associated with the occurrence of SWD among shiftworking nurses on rapid-rotation schedules. (Author correspondence: yuinoue@tokyo-med.ac.jp)     

SHIFTWORK,WORK-FAMILY CONFLICT AMONG ITALIAN NURSES,AND PREVENTION EFFICACY

Shiftwork may be a demanding situation because it raises problems for reconciling work and nonwork activities; as such, this conflict may be mitigated by designing and implementing effective preventative actions at the workplace. There is a paucity of research directly examining the impact of work schedules and preventative measures at work on work-family conflict. Hence, the authors posed the following questions in their study: What is the impact of different work schedules on work-family conflict? Is a preventative culture associated with less work-family conflict? Is work-family conflict associated with specific health and well-being indicators and if so, how does work-family conflict affect well-being as compared with other potential determinants? A subset of 750 nurses (≈10% of total workforce) were randomly selected from a larger sample. Nurses completed the Italian version of the NEXT questionnaire plus newly developed items to create an index on occupational safety and health prevention at work. Data were explored using two data mining techniques, Random Forests and Bayesian Networks, and modeled using hierarchical linear regression models. In all, 664 (88.5% of sample) nurses answered the questionnaire. The authors found that different work schedules had a differential impact on work-family conflict. In addition, effective risk communication between workers and people in charge of safety and health, and participation in preventative activities, quantitative workload, performing tasks not belonging to the nursing profession, and the number of weekends/month spent at work were all strongly associated with work-family conflict. The variable “time schedules” also acted as an effect modifier in the relationship between effective communication and participation in preventative activities and work-family conflict. In addition, quantitative demands played a role as a mediator (30% of total effect) in the relationship between effective communication and participation in preventative activities and work-family conflict. Work-family conflict was significantly associated with burnout, sleep, and presenteeism; its association with burnout was higher than other precursors. Shift schedules that involved night work implied different workload demands, less effective communication, and participation in preventative activities than the other work schedules considered. The presence of a preventative culture directly reduced work-family conflict and indirectly via reduction of work demands. The authors conclude that the development of a preventative culture among irregular and night shiftworkers can be effective in reducing work-family conflict, while positively increasing well-being and job performance. (Author correspondence: donatella.camerino@unimi.it)     

Shiftworkers in developing countries: health and well-being and supporting measures

Developing countries currently represent approximately 79% of the world population. Living and working conditions in middle and low income countries are harder and worse than for workers in industrialized countries. In developing countries, workers usually face more dangerous workplaces and unhealthy environmental and occupational conditions than those of industrial countries. Shiftworkers can face even more difficulties, due to constraints caused by their working time and consequences on health. Occupational health actions oriented by health policies were implemented during the 1990s in several Asian countries and in Brazil. these actions are important to promote workers' health. The general aims of this report are: a) to discuss topics related to equity and health; b) to present the main items of international and Brazilian legislation for shiftworkers; and c) to review general and specific measures of occupational health for shiftworkers in developing countries. In order to have equity on health and well-being, supporting measures should encompass micro and macro improvements at local, regional and national levels. Governmental and non-governmental organizations, professional bodies, labor unions, research institutes, universities, technical schools and syndicates, would play important roles to achieve these goals.     

生态系统健康与生物多样性*

生态系统健康学是一门研究人类活动、社会组织、自然系统及人类健康的整合性学科,主要探讨资源环境管理对策,以及生态系统健康与人类健康的关系。生态系统健康是人类健康的基础,是人类可持续发展的重要前提,维护生态系统健康,保护生物多样性,也就是维护人类生存的机会。人类健康依附于健康的生态系统功能和服务日益为人们所认识,关注和理解生物多样性、生态系统健康、人类健康之间的相互联系已成为全球可持续发展的必要条件。本文着重综述了生态系统健康的研究内容及全球环境变化背景下生物多样性的变化对生态系统健康的影响效应。     

Exploring sleepiness and entrainment on permanent shift schedules in a physiologically based model

The effects of permanent shift work on entrainment and sleepiness are examined using a mathematical model that combines a model of sleep-wake switch in the brain with a model of the human circadian pacemaker entrained by light and nonphotic inputs. The model is applied to 8-hour permanent shift schedules to understand the basic mechanisms underlying changes of entrainment and sleepiness. Average sleepiness is shown to increase during the first days on the night and evening schedules, that is, shift start times between 0000 to 0700 h and 1500 to 2200 h, respectively. After the initial increase, sleepiness decreases and stabilizes via circadian re-entrainment to the cues provided by the shifts. The increase in sleepiness until entrainment is achieved is strongly correlated with the phase difference between a circadian oscillator entrained to the ambient light and one entrained to the shift schedule. The higher this phase difference, the larger the initial increase in sleepiness. When entrainment is achieved, sleepiness stabilizes and is the same for different shift onsets within the night or evening schedules. The simulations reveal the presence of a critical shift onset around 2300 h that separates schedules, leading to phase advance (night shifts) and phase delay (evening shifts) of the circadian pacemaker. Shifts starting around this time take longest to entrain and are expected to be the worst for long-term sleepiness and well-being of the workers. Surprisingly, we have found that the circadian pacemaker entrains faster to night schedules than to evening ones. This is explained by the longer photoperiod on night schedules compared to evening. In practice, this phenomenon is difficult to see due to days off on which workers switch to free sleep-wake activity. With weekends, the model predicts that entrainment is never achieved on evening and night schedules unless the workers follow the same sleep routine during weekends as during work days. Overall, the model supports experimental observations, providing new insights into the mechanisms and allowing the examination of conditions that are not accessible experimentally.     

Influence of flexibility and variability of working hours on health and well-being

Flexible working hours can have several meanings and can be arranged in a number of ways to suit the worker and/or employer. Two aspects of “flexible” arrangement of working hours were considered: one more subjected to company control and decision (variability) and one more connected to individual discretion and autonomy (flexibility). The aim of the study was to analyze these two dimensions in relation to health and well-being, taking into consideration the interaction with some relevant background variables related to demographics plus working and social conditions. The dataset of the Third European Survey on working conditions, conducted in 2000 and involving 21,505 workers, was used. Nineteen health disorders and four psycho-social conditions were tested by means of multiple logistic regression analysis, in which mutually adjusted odds ratios were calculated for age, gender, marital status, number of children, occupation, mode of employment, shift work, night work, time pressure, mental and physical workload, job satisfaction, and participation in work organization. The flexibility and variability of working hours appeared inversely related to health and psycho-social well-being: the most favorable effects were associated with higher flexibility and lower variability. The analysis of the interactions with the twelve intervening variables showed that physical work, age, and flexibility are the three most important factors affecting health and well-being. Flexibility resulted as the most important factor to influence work satisfaction; the second to affect family and social commitment and the ability to do the same job when 60 years old, as well as trauma, overall fatigue, irritability, and headache; and the third to influence heart disease, stomachache, anxiety, injury, and the feeling that health being at risk because of work. Variability was the third most important factor influencing family and social commitments. Moreover, shift and night work confirmed to have a significant influence on sleep, digestive and cardiovascular troubles, as well and health and safety at work. Time pressure also showed a relevant influence, both on individual stress and social life. Therefore, suitable arrangements of flexible working time, aimed at supporting workers' coping strategies, appear to have a clear beneficial effect on worker health and well-being, with positive consequences also at the company and social level, as evidenced by the higher “feeling to be able to work until 60 years of age”.     

Beneficial effects on employment and preventive health care: the concept and results of counselling processes from a German project

Since December 1998 a project of working time counselling named "Design of Modern Working Times" is supported by the federal state of North Rhine-Westphalia in Germany and the European Union; AWiS-consult is entrusted to carry out this project. The service offered to all companies, institutions, work committees, and employees interested covers information, assessment of existing working time schedules, development of alternative or new working time schedules, and accompanying implementation processes. Up to June 2001 nearly 300 inquiries were worked on, most of them from industry, service companies, and from the field of care and hospitals. Working time design in this project aims not only at work safety and health care but also at beneficial effects on employment. In a special campaign from May 2000 to May 2001, 61 companies were supported by AWiS-consult, with the result of more than 400 new employees and 16 companies with employment secured, so the combination of preventive health care and beneficial effects on employment by working time design can be assessed as successful.     

A prospective multiple case study of the impact of emerging scientific evidence on established colorectal cancer screening programs: a study protocol

In this editorial, we reflect on the arguments for starting a scientific society focused on research on how to improve healthcare. This society would take an inclusive approach to what constitutes healthcare. For instance, it should include mental health healthcare, treatment for substance abuse, the work of allied health professions, and preventive healthcare. The society would be open to researchers from all traditions. Thus, we take an inclusive approach to what constitutes scientific research, as long as it uses rigorous methods, is focused on improving healthcare, and aims at knowledge that can be transferred across settings. The society would primarily target scientific researchers but would invite others with an interest in this area of research, regardless of their discipline, position, field of application, or group affiliation (e.g., improvement science, behavioral medicine, knowledge translation). A society would need fruitful collaboration with related societies and organizations, which may include having combined meetings. Special links may be developed with one or more journals. A website to provide information on relevant resources, events, and training opportunities is another key activity. It would also provide a voice for the field at funding agencies, political arenas, and similar institutions. An organizational structure and financial resources are required to develop and run these activities. Our aim is to start an international debate, to discover if we can establish a shared vision across academics and stakeholders engaged with creating scientific knowledge on how to improve healthcare. We invite readers to express their views in the online questionnaire accessed by following the URL link provided at the end of the editorial.     

Why artificial light at night should be a focus for global change research in the 21st century

The environmental impacts of artificial light at night have been a rapidly growing field of global change science in recent years. Yet, light pollution has not achieved parity with other global change phenomena in the level of concern and interest it receives from the scientific community, government and nongovernmental organizations. This is despite the globally widespread, expanding and changing nature of night‐time lighting and the immediacy, severity and phylogenetic breath of its impacts. In this opinion piece, we evidence 10 reasons why artificial light at night should be a focus for global change research in the 21st century. Our reasons extend beyond those concerned principally with the environment, to also include impacts on human health, culture and biodiversity conservation more generally. We conclude that the growing use of night‐time lighting will continue to raise numerous ecological, human health and cultural issues, but that opportunities exist to mitigate its impacts by combining novel technologies with sound scientific evidence. The potential gains from appropriate management extend far beyond those for the environment, indeed it may play a key role in transitioning towards a more sustainable society.     

DEPRESSED MOOD IN THE WORKING POPULATION: ASSOCIATIONS WITH WORK SCHEDULES AND WORKING HOURS

The impact of working time arrangements (WTA) on health has been studied extensively. Still, little is known about the interrelation between work schedules, working hours, and depressed mood. For work schedules, the underlying assumptions regarding depressed mood refer to a disturbance of social and biological rhythms, whereas for working hours, the assumptions relate to workload and work capacity. Conversely, depressed mood may urge an employee to adjust his/her work schedule and/or number of working hours/week (h/wk). The aim of this study was to assess the association between work schedule and working hours with depressed mood. Using baseline data from the Maastricht Cohort Study, depressed mood in day work was compared with depressed mood in different shiftwork schedules (n?=?8843). Within day work, several categories of working h/wk were studied in association with depressed mood (n?=?7217). The association between depressed mood and several aspects of overtime was assessed separately. Depressed mood was measured with a dichotomous item: “Did you feel down every day over the last two weeks?” Separate logistic regression analyses were conducted for men and women, with adjustments for potential confounders. The odds ratio (OR) for depressed mood was greater for men involved in shiftwork than for men only involved in day work (three-shift OR?=?2.05 [95% confidence interval, CI 1.52–2.77]; five-shift OR?=?1.34 [95% CI 1.00–1.80]; irregular-shift OR?=?1.79 [95% CI 1.27–2.53]). In female employees, five-shift work was associated with a higher prevalence of depressed mood (OR?=?5.96 [95% CI 2.83–12.56]). Regarding the number of working h/wk, men working <26?h/wk had a higher prevalence of depressed mood than men working 36–40?h/wk (OR?=?2.73 [95% CI 1.35–5.52]). After conducting trend analyses, a significant decreasing trend was found in men, whereas an increasing trend was found in women working a high number of hours. Furthermore, a dose-response relationship was present in men regarding the number of overtime h/wk. This study showed that different work schedules and working hours are associated with depressed mood. Shiftwork was related to a higher prevalence of depressed mood than day work. The association was more pronounced for male employees. Regarding the number of working h/wk, male and female employees showed an opposite trend in depressed mood. Because of the possibility of a healthy worker effect and the possibility of a reciprocal relationship between WTA and depressed mood, the reported relation might be underestimated. This study has illustrated that occupational physicians, who deal with depressed mood among workers, should carefully consider the impact of WTA. (Author coorespondence: Karolien.Driesen@epid.unimaas.nl)