Seasonal Impacts on Sleep in Arctic Shift Workers: Insights from Wearable Monitoring

Introduction: Studies suggest that seasons may influence sleep, though findings are inconsistent. In Arctic settings, the extreme light conditions including polar night (dark season) and midnight sun (light season) may have a distinct impact on the relationship between shift work and sleep. This observational crossover study aimed to examine seasonal variations in sleep among Arctic shift workers using both subjective and objective sleep measures.

Methods: A cohort of 112 rotational shift working process operators (mean age 32 ± 11.3 years, 21% women) from an industrial plant at 71°N in Norway participated during both light and dark seasons. Their work schedule included seven consecutive morning shifts and seven consecutive night shifts, separated by four rest days. Objective sleep duration was measured over 20 days with the Oura smart ring, while subjective sleep was measured over 25 days by sleep diary.

Results: Preliminary results indicate that objectively measured sleep duration (minutes; mean ± SEM) after night shifts was slightly longer in the dark season 385 ± 4 compared with the light season 374 ± 4. The opposite trend was observed for seasonal effects on sleep after morning shifts: 379 ± 3 in the dark season; 387 ± 3 in the light season. Sleep on free days followed the same pattern as morning shifts, with shorter duration in the dark season (443 ± 6) compared with the light season (452 ± 6). Overall, our findings indicate that sleep duration tends to be longer on free days than on workdays. The timing of sleep measured objectively as mid-sleep (hours past midnight), was similar after night shifts across dark and light seasons; at 11.6 and 11.5, respectively. Mid-sleep during the dark and light seasons after morning shifts occurred at 3.0 and 3.3; and on free days, at 5.7 and 6.0; respectively. Subjective sleep duration (minutes; mean ± SEM) in dark and light season after night shifts was 404 ± 5 and 406 ± 5; after morning shifts 411 ± 5 and 404 ± 4; and on free days 492 ± 8 and 489 ± 6, respectively. These subjective ratings were somewhat higher than the objective measures.

Conclusion: Our data suggests that night shifts and seasonal variations have only a minor impact on objective and subjective measures of total sleep duration among these Arctic shift workers. Follow-up analyses will explore potential underlying factors, day-to-day variation and individual variability. Support: This research is supported by the RRESEARCH COUNCIL OF NORWAY; the PETROMAKS2 program ID# 326291.

Publication History

Article published online:
08 October 2025