O-47 Beyond night work: why shift work without night work may still be harmful

Abstract

<h3>Objective</h3> Most literature examining the health effects of shift work prioritize night work as the exposure of interest. However, little attention has been paid to the co-occurrence of working time characteristics beyond shift type (e.g. night vs day) that may lead to circadian rhythm disruption; characteristics such as shift intensity, shift duration, rotation pattern, and weekend work. We hypothesize that the co-occurrence of these characteristics with and without night work could explain why shift work without night work is sometimes associated with adverse health effects. <h3>Methods</h3> Time-registry data on 14,430 full-time (&gt;150 shifts/year) healthcare workers from 2012–2016 were sourced from the Working Hours in the Finnish Public Sector (WHFPS) study to describe the prevalence and co-occurrence of working time characteristics that may lead to circadian rhythm disruption. First, each characteristic (type, intensity, duration, rotational pattern, and weekend work) was cross-classified in a matrix to examine its co-occurrence with all other characteristics (e.g. how many night shifts were also long shifts). Second, the prevalence of each working hour characteristic by annual shift schedules (permanent or rotating day/evening/night) were examined. <h3>Results</h3> Our results provide evidence that working hour characteristics hypothesized to cause circadian rhythm disruption have a varying distribution with each other and across shift schedules- even schedules that don’t include nights. While day shifts are thought to not cause circadian rhythm disruption, 32% of day shifts versus 34% of night shifts co-occurred with long work hours, quick returns, and rotations. Furthermore, despite not including nights, the Day/Evening schedule had more quick returns than the Day/Evening/Night schedule and still contained rotations, long hours, and weekend work. <h3>Conclusion</h3> Thus, a cautious interpretation of the association between night work and human health may be warranted, as circadian rhythm disruption may be caused by long hours, rotations, or quick returns which may or may not accompany night work.