0399 Sleep Timing in Relation to Circadian Phase and Turnover in Early-Morning Shift Workers

Abstract Introduction Shiftwork is associated with numerable adverse health outcomes including cardiovascular disease, obesity, and depression. Additionally, turnover intention is higher in those working shiftwork, however these feelings are not ubiquitous. Reasons why some individuals contemplate leaving their role during shiftwork, while others do not, have yet to be established. One mechanism may be the degree of circadian alignment an individual experiences during shiftwork. Thus, we investigated the relationship between turnover intention and the timing of sleep in relation to circadian phase (i.e., phase angle of entrainment) in new bus operators during their transition to early-morning shiftwork. Methods Twenty-eight volunteers (9 female; aged average ± SD 35.4 ± 7.1yr) underwent an ~8h evening in-laboratory stay in dim-lighting ( 5 lux) and completed a 1-week sleep diary during a day-oriented onboarding. Following onboarding, operators either transitioned to a shiftwork schedule (n=21; 33% of shifts starting before 7am) or maintained a daywork schedule (n=7; 33%) and completed weekly diaries over 17 weeks to capture turnover intention. Circadian phase was determined via salivary dim-light melatonin onset (DLMO; 3pg/ml) and phase angle was calculated by average onboarding sleep onset minus DLMO. Turnover intention was measured via survey with the question “I am seriously thinking about quitting my job” with Likert-scale responses of 1-Strongly Disagree to 5-Strongly Agree, with the highest score calculated for each participant. Associations between phase angle and turnover intention were calculated by group via Pearson Correlation. Results There was a significant negative correlation between phase angle and turnover intention within the shiftwork group (r=-0.46, p=0.04), such that narrower phase angle correlated with higher intention to leave; there was no significant association within the daywork group (r=0.63, p=0.13). Conclusion During the transition to an early-morning shiftwork schedule, a narrower phase angle was associated with higher turnover intention in those working shiftwork but not daywork. These findings could explicate a mechanism by which some individuals consider changing roles during shiftwork. Further research into circadian alignment and turnover intention, particularly in overnight shift workers, could elucidate possible intervention targets to promote wellbeing and reduce turnover intention in shift working employees. Support (if any) OHSU School of Nursing PhD Student Scholarship Award