Objectives: The aim was to investigate how working in an extreme and isolated environment in the Arctic affected the diurnal rhythm of saliva cortisol.
Study design: Field study.
Methods: Twenty-five male tunnel workers were screened during 3 different working cycles with different light conditions during a 9-month construction period; April/May (24 hours [h] light), September/October (approximately 12 h light and 12 h darkness) and November/December (24 h darkness). The work schedule was 10 h on/14 h off, 21 days at work/21 days off work. The workers alternated between the day shift in 1 work period and the night shift in the next. Four saliva samples were collected on day 14 in all 3 periods; immediately after awakening, and then 30 minutes, 6 hours and 12 hours after awakening.
Results: Regardless of shift schedule, the workers' cortisol levels were significantly lower in the period with 24 hours of light per day compared to the period with "normal" light conditions. There were no differences in the cortisol levels of the workers on night shifts in the period with 24 hours of darkness compared to those in the period with "normal" light conditions, but the workers who were on day shifts in the period with 24 of hours darkness had a disturbed cortisol rhythm (lower peak after awakening and lack of the normal decrease during the day).
Conclusions: External light conditions and shift schedule were important factors in regulating the workers' cortisol rhythm. It seems to be easier to adapt to a night rhythm than an early morning rhythm in an isolated and extreme environment.