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Title: Temporal dynamics of circadian phase shifting response to consecutive night shifts in healthcare workers: role of light-dark exposure.
Austin Authors: Stone, Julia E;Sletten, Tracey L;Magee, Michelle;Ganesan, Saranea;Mulhall, Megan D;Collins, Allison L ;Howard, Mark E ;Lockley, Steven W;Rajaratnam, Shantha M W
Affiliation: Cooperative Research Centre for Alertness, Safety and Productivity, Melbourne, Victoria, Australia
School of Psychological Sciences and Monash Institute of Cognitive and Clinical Neurosciences, Faculty of Medicine, Nursing & Health Sciences, Monash University, Clayton, Victoria, Australia
Institute for Breathing and Sleep, Austin Health, Heidelberg, Victoria, Australia
Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, Massachusetts, USA
Division of Sleep Medicine, Harvard Medical School, Boston, Massachusetts, USA
Issue Date: Jun-2018
Date: 2018-04-06
Publication information: The Journal of physiology 2018; 596(12): 2381-2395
Abstract: Shift work is highly prevalent and is associated with significant adverse health impacts. There is substantial inter-individual variability in the way the circadian clock responds to changing shift cycles. The mechanisms underlying this variability are not well understood. We tested the hypothesis that light-dark exposure is a significant contributor to this variability; when combined with diurnal preference, the relative timing of light exposure accounted for 71% of individual variability in circadian phase response to night shift work. These results will drive development of personalised approaches to manage circadian disruption among shift workers and other vulnerable populations to potentially reduce the increased risk of disease in these populations. Night shift workers show highly variable rates of circadian adaptation. This study examined the relationship between light exposure patterns and the magnitude of circadian phase resetting in response to night shift work. In 21 participants (nursing and medical staff in an intensive care unit) circadian phase was measured using 6-sulphatoxymelatonin at baseline (day/evening shifts or days off) and after 3-4 consecutive night shifts. Daily light exposure was examined relative to individual circadian phase to quantify light intensity in the phase delay and phase advance portions of the light phase response curve (PRC). There was substantial inter-individual variability in the direction and magnitude of phase shift after three or four consecutive night shifts (mean phase delay -1:08 ± 1:31 h; range -3:43 h delay to +3:07 h phase advance). The relative difference in the distribution of light relative to the PRC combined with diurnal preference accounted for 71% of the variability in phase shift. Regression analysis incorporating these factors estimated phase shift to within ±60 min in 85% of participants. No participants met criteria for partial adaptation to night work after three or four consecutive night shifts. Our findings provide evidence that the phase resetting that does occur is based on individual light exposure patterns relative to an individual's baseline circadian phase. Thus, a 'one size fits all' approach to promoting adaptation to shift work using light therapy, implemented without knowledge of circadian phase, may not be efficacious for all individuals.
DOI: 10.1113/JP275589
ORCID: 0000-0002-0005-7838
Journal: The Journal of physiology
PubMed URL: 29589871
Type: Journal Article
Subjects: circadian
phase shift
shift work
Appears in Collections:Journal articles

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