Length of exposure to long working hours and night work and risk of sickness absence: a register-based cohort study

Abstract

Background There is inconsistent evidence that long working hours and night work are risk factors for sickness absence, but few studies have considered variation in the length of exposure time window as a potential source of mixed findings. We examined whether the association of long working hours and night work with sickness absence is dependent on the length of exposure to the working hour characteristics. Methods We analysed records of working hours, night work and sickness absence for a cohort of 9226 employees in one hospital district in Finland between 2008 and 2019. The exposure time windows ranged from 10 to 180 days, and we used Cox’s proportional hazards models with time-dependent exposures to analyse the associations between working-hour characteristics and subsequent sickness absence. Results Longer working hours for a period of 10 to 30 days was not associated with the risk of sickness absence whereas longer working hours for a period of 40 to 180 days was associated with a lower risk of sickness absence. Irrespective of exposure time window, night work was not associated with sickness absence. Conclusions It is important to consider the length of exposure time window when examining associations between long working hours and sickness absence, whereas the association between night work and sickness absence is not similarly sensitive to exposure times.

A Longitudinal Study on Trajectories of Night Work and Sickness Absence among Hospital Employees

“…The healthy worker effect assumes that those who work nights irregular working hours might be a selected population which may be seen in a relatively stable and large number of employees who did not work nights at all in the 12-year follow-up. This might also shed some light on why the increased risk of SA has not been seen in all earlier studies [22].…”

“…Such a study with a detailed frequency of night shifts and assessment of SA might be among the first with such a comprehensive period of 12 years. Earlier studies have focused on limited assessment time periods for night work [22][23][24] or have applied prospective study designs in which night work has been assessed at one time-point at baseline [19]. Another strength of our study is in separate trajectories of night shifts for those with and without SA.…”

“…There are also some limitations of this study. Besides the designs of earlier studies on night work, measures of SA have varied, limiting the comparability of findings [19,[22][23][24]. While earlier studies used various measures of SA, e.g., short (≤7 days), long SA (≥7 days) [21], or very long (≥30 consecutive days) SA [19], in this study, only the first SA episode without assessment of the length was evaluated.…”

“…However, longitudinal assessments of night work and how the frequency of night work may change in anticipation of healthrelated outcomes such as SA are scarce. To date, most studies have focused on limited assessment time periods for night work [22][23][24] or have applied prospective study designs in which night work has been assessed at one time-point at baseline [19].…”

The Time-Varying Effect of Participatory Shift Scheduling on Working Hour Characteristics and Sickness Absence: Evidence from a Quasi-Experiment in Hospitals

“…Evidence from a systematic review on nurses suggests that the health problems associated with shift work are mediated by at least chronotype and sex [ 13 ]. Besides selection or individual preferences, a study from Finnish healthcare found that there is no association between longer working hours and the risk of sickness absence in the short exposure time of 10 to 30 days, and the risk is lower on exposure of 40 days or more [ 14 ], suggesting that the exposure time window plays an important role in the potential health effects of long working hours. Other studies on nurses have found that it is not only shift work that affects health, but rather how shift work is organized in terms of weekly hours, irregular schedules, and length of recovery periods [ 11 , 15 , 16 , 17 ].…”