The mutual relationship between shift work and depressive complaints--a prospective cohort study.

OBJECTIVE: The aim of this study was to examine longitudinally the mutual relationship between shift work and depressive complaints. METHODS: Data from the ongoing Maastricht cohort study (1998-2008) were used. Firstly, the impact of shift work on the development of depressive complaints, defined as depressed mood, was studied. Both prospective and retrospective approaches were used, conducting, respectively, survival and logistic regression analyses, correcting for possible confounding factors. Secondly, the impact of depressed mood on changes in shift work at one-year follow-up was studied. All analyses were stratified for men and women and, where possible, for age (<45 versus ≥45 years). RESULTS: Overall, the impact of shift work on the development of depressed mood over a ten-year period was rather small, although, male shift workers ≥45 years did contribute to a higher risk of developing depressed mood [hazard risk (HR) 1.37, 95% confidence interval (95% CI) 1.01-1.86]. Retrospective analyses found higher odds of depressed mood and depressive disorder among former or current male shift workers than "never shift workers" [odds ratio (OR) 1.39, 95% CI 1.09-1.79 and OR 1.79, 95% CI 1.32-2.42, respectively]. Results lacked significance when correcting for demographic and work-related factors. Analyses studying the impact of depressed mood on changes in work schedules showed that the risk to change from shift to day work or from shift work to sick leave was higher when depressed mood was reported at baseline [relative risk (RR) shift to day work 1.98, 95% CI 1.13-3.47; RR shift work to sick leave 2.96, 95% CI 2.00-4.29]. CONCLUSIONS: Although shift work did not have a large impact on the development of depressed mood, results might be underestimated due to selection processes and possibly overcorrection.

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.