8289524 Permanent night work and risk of injuries: a register-based cohort study

<h3>Objectives</h3> Night work has been associated with a higher risk of injuries, but the extent to which the impact of different types of night work schedules influences the risk remains unclear. This study examines whether the risk of injuries differs between employees with permanent night work and those with other shift schedules, including rotating shift work with night shifts. <h3>Materials and Methods</h3> We conducted a nationwide register-based cohort study using payroll data from the Danish Working Hour Database (DAD), which comprises day-by-day information about working hours among hospital employees. Based on the proportion of night, evening, and day shifts worked in the preceding 52 weeks, the following sic work schedules were applied: permanent day; permanent evening; permanent night; day/evening; day/night; evening/night, and day/evening/night. Injuries were identified using the Danish National Patient Register by use of a unique personal identifier applied to all residents. Poisson regression with generalized estimating equations (GEE) was applied with a running window of one day to estimate incidence rate ratios (IRRs) for injuries on the following day by work schedule. Main analyses were adjusted for sex, age, and job type. <h3>Results</h3> Among 191,224 employees contributing 179 million observation days, permanent night workers had a lower injury risk compared with all other work schedules, except permanent day workers (IRR; CI). Compared to permanent night workers, the highest injury risk was observed among evening/night workers (IRR=1.38; 95% CI: 1.19–1.59) and day/evening/night workers (IRR=1.30; 95% CI: 1.19–1.42). <h3>Conclusion</h3> Our results suggest that permanent night workers have lower injury risk than rotating shift workers with night shifts. Differences in work tasks, adaptation, and selection effects may contribute to this pattern. <h3>Funding</h3> The current project was funded by research grants from The Danish Working Environment Research Fund (23-2017-09) and the National Research Centre for the Working Environment. Denmark.