Occupational
Quantifying cumulative exposure to circadian disruption based on lifetime shift work information and biological sleep-wake timing in female nurses Linske de Bruijn* Linske de Bruijn Nina E. Berentzen Jelle J. Vlaanderen Roel C.H. Vermeulen Hans Kromhout Flora E. van Leeuwen Michael Schaapveld
Background: Shift work-induced circadian disruption (CD) may affect health. In epidemiological research, night shift work exposure and its frequency are mainly used as proxies for CD. However, night shift work may inadequately reflect CD as workers may also experience CD during other shift types if these shifts interfere with a worker’s biological night. We aim to quantify individual cumulative CD based on past shift work and preferred sleep-wake timing in a cohort of nurses.
Methods: Data were derived from 59,947 Dutch female nurses who participated in the Nightingale Study (18-65 years (y) at baseline in 2011; mean [SD] age: 46.9y [11.0]). They retrospectively reported their job history since the start of their nursing career including start-stop years and shift-specific duration and frequency, allowing us to assess their cumulative exposure to shift work. In 2017, this information was updated in a second questionnaire (n=37,731, 63%) and additionally, sleep timing was collected (preferred sleep and wake time in a work-free period) and used to define biological night. To determine the individual cumulative exposure to CD, we quantified the overlap in hours (h) between shift work times and the biological night for 35,006 nurses.
Results: Regarding specific shift types, the median CD was 9.0 h (IQR 8.5-9.5) for night shifts, 2.5 h (2.3-3.3) for morning, and 1.0 h (0.5-1.5) for evening shifts (Figure). The median cumulative CD was 4,404 h (1,032-9,861) and ranged from 1,584 h in nurses with a work duration <10y to 8,285 h in nurses with a work duration ≥30y. Night shift work exposure (never/ever) and its frequency explained 13% and 33% of the variance in CD, respectively.
Conclusion: We assessed the cumulative shift work-related CD of nurses. CD is just partly correlated to classical measures of night shift work exposure as used in most epidemiological studies. This novel cumulative exposure metric may improve association studies on exposure to CD and health issues.
