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0261 The effects of night work and light exposure on salivary melatonin concentration during work days and days off
  1. Stine Daugaard1,
  2. Anne Helene Garde2,3,
  3. Jens Peter Bonde3,4,
  4. Jens Christoffersen5,
  5. Aase Marie Hansen3,
  6. Jakob Markvart6,
  7. Vivi Schlünssen2,7,
  8. Debra Skene8,
  9. Helene Tilma Vistisen1,
  10. Henrik Kolstad1
  1. 1Department of Occupational Medicine, Danish Ramazinni Centre, Aarhus University Hospital, Aarhus, Denmark
  2. 2National Research Centre for the Working Environment, Copenhagen, Denmark
  3. 3Institute of Public Health, Copenhagen University, Copenhagen, Denmark
  4. 4Department of Occupational Medicine, Bispebjerg Hospital, Copenhagen, Denmark
  5. 5Stakeholder Communications and Sustainability, VELUX, Hørsholm, Denmark
  6. 6Department of Energy Performance, Indoor Environment and Sustainability of Buildings, Danish Building Research Institute, Aalborg University, Copenhagen, Denmark
  7. 7Department of Public Health, Aarhus University, Aarhus, Denmark
  8. 8Chronobiology, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK


Objective We aimed to examine the effects of night work on salivary melatonin concentrations during and subsequent to night work and the mediating role of light.

Methods We included 254 day workers and 87 night workers that were followed during 322 work days and 301 days off work. Each day was defined as the 24 hour period starting from the beginning of a night shift or awakening in mornings with daytime work and days off. Light levels were recorded and synchronised with diary information on start and end of sleep and work. On average, participants provided four saliva samples per day, and these were analysed for melatonin concentration. Differences between day and night workers on work days and days off were assessed with multilevel regression models with melatonin concentrations as outcome. All models were stratified or adjusted by time of the day. For light exposure, we estimated the total, direct, and indirect effects of night work on melatonin concentrations obtaining 95% confidence intervals trough bootstrapping.

Results On work days, night workers showed 16.5% (95% CI 0.2; 30.5) lower salivary melatonin concentration compared with day workers. Light exposure seemed to mediate about 40% of the melatonin suppression seen during night, but no mediating effect of light was seen during day time. On days off, we observed no difference in melatonin concentration between day and night workers.

Conclusion These findings are in accordance with a transient and partly light mediated effect of night work on melatonin concentration.

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