Andreas Næss Holme

• Holme, Andreas Næss; Moen, Line Victoria; Sallinen, Mikael; Nilsen, Kristian Bernhard; Boccara, Charlotte & Phillips, Andrew JK [Show all 8 contributors for this article] (2026). Adaptation across consecutive night shifts at 71°N under Arctic summer daylight and winter darkness. Effects on alertness, sleepiness, and fatigue. Scandinavian Journal of Work, Environment and Health. ISSN 0355-3140. 52(4), p. 403–414. doi: 10.5271/sjweh.4295. Full text in Research Archive Show summary

  Objectives: This study aimed to investigate how alertness, sleepiness, and fatigue change across consecutive night compared to morning shifts among Arctic shift workers and whether these effects differ between seasons of midnight sun and polar night. Methods: We conducted an observational crossover study of 118 shift workers from an industrial plant at a high latitude (71°N) in northern Norway. Eighty-one individuals participated in both the light (near 24-hour daylight) and dark (minimal natural light) seasons. Work schedules included blocks of seven consecutive morning shifts and seven consecutive night shifts, separated by four rest days. Alertness (psychomotor vigilance test), subjective sleepiness (Karolinska Sleepiness Scale), and subjective fatigue were measured at the end of shifts on days 1, 3, and 6 of each shift block. We analyzed data using multilevel mixed-effects regression models with season, shift type (morning/night), and consecutive workday number as fixed effects. Results: Night shifts were linked to lower alertness and higher sleepiness and fatigue in both seasons, with the largest impairments on the first night. Across six consecutive night shifts, alertness improved and sleepiness and fatigue decreased, with similar trajectories in both seasons. There was no evidence that season significantly affected alertness, sleepiness, or fatigue. Conclusions: Night shifts generally impair alertness and increase sleepiness and fatigue, yet outcomes improved across consecutive nights. Despite the well-established effects of natural light on circadian rhythms, the seasonal photoperiod altered neither the shift-related impairments in alertness, sleepiness or fatigue nor the subsequent improvements across consecutive nights; workers showed similar adaptation in both seasons.

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• Holme, Andreas Næss; Moen, Line Victoria; Sallinen, Mikael; Nilsen, Kristian Bernhard; Boccara, Charlotte & Haugen, Fred [Show all 7 contributors for this article] (2026). Night Shift Work as an Arctic Hazard: Do Seasonal Light Extremes Affect Alertness, Sleepiness, and Fatigue? Full text in Research Archive Show summary

  Introduction: Light is the primary entrainment mechanism (‘zeitgeber’) of the circadian clock. Its sensitivity to light means that seasonal changes in photoperiod can affect circadian entrainment in shift workers, potentially influencing their adaptation to night work. At high latitudes, such as the Arctic, extreme daylight variations across seasons provide a unique context for studying consequences of such light sensitivity. Polar nights and midnight sun may further challenge circadian entrainment mechanisms. Whether shift work and seasonal variations cumulate or combine their effect in the photoperiodic zeitgeber remains unclear. This study investigates how seasonal variations may interact with consecutive morning and night shifts to impact alertness, sleepiness and fatigue in shift workers. Methods: We recruited 112 three-shift process operators at 71°N, among which 81 participated during both the dark and light seasons. The work schedule included seven consecutive morning shifts and seven consecutive night shifts, separated by four rest days. Objective alertness was measured by the 3-minute Psychomotor Vigilance Task (PVT-B), using lapses (omissions ≥355ms) and response speed (inverse response time) as outcome variables. Subjective sleepiness and fatigue were assessed by the Karolinska Sleepiness Scale (KSS) and a separate question to assess mental fatigue, respectively. Tests were conducted at the end of shift on days 1, 3, and 6 of each 7-day shift block. Data were analysed using multilevel linear mixed-effects regression models with season, shift type (morning/night) and consecutive workday number as fixed effects. Results: Night shifts were associated with lower alertness and higher levels of sleepiness and fatigue, especially on the first night shift, compared to morning shifts. Furthermore, the results indicated significant improvements in alertness and reduced sleepiness and fatigue over the consecutive six night shifts. There was no effect of season on any of the outcome variables. Conclusion: These findings suggest that while night shifts generally impair alertness, as well as increase sleepiness and fatigue, workers may gradually adapt over consecutive shifts, as evidenced by improvements by the sixth night. The lack of significant seasonal effects on sleepiness and fatigue suggests that workers might adapt equally well to night shifts regardless of the photoperiod.

• Moen, Line Victoria; Holme, Andreas Næss; Matre, Dagfinn & Haugen, Fred (2025). Seasonal Impacts on Sleep in Arctic Shift Workers: Insights from Wearable Monitoring. Sleep Science. ISSN 1984-0659. 18(S2), p. S1–S1. doi: 10.1055/s-0045-1812747. Full text in Research Archive Show summary

  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.

• Holme, Andreas Næss; Moen, Line Victoria; Sallinen, Mikael; Nilsen, Kristian Bernhard; Boccara, Charlotte & Haugen, Fred [Show all 7 contributors for this article] (2025). Night Work During Midnight Sun and Polar Nights: Impact on Alertness, Sleepiness and Fatigue. doi: 10.1055/s-0045-1812737. Full text in Research Archive Show summary

  Introduction: The circadian clock's sensitivity to light means that seasonal changes in photoperiod can affect circadian entrainment in shift workers, thus influencing their adaptation to night work. At high latitudes, such as the Arctic, extreme daylight variations across seasons, provide a unique context for studying such circadian disruption. Polar nights and midnight sun may further challenge circadian entrainment mechanisms. Whether shift work and seasonal variations cumulate or combine their effect in the photoperiodic zeitgeber remains unclear. This study investigates how seasonal variations may interact with consecutive morning and night shifts to impact alertness, sleepiness and fatigue. Methods: We recruited 112 three-shift process operators at 71°N, among which 84 participated during both the dark and light seasons. Their work schedule included blocks of seven consecutive morning shifts and seven consecutive night shifts, separated by four rest days. Alertness was measured by the 3-minute Psychomotor Vigilance Task (PVT-B), using lapses (omissions ≥355ms) and response speed (inverse response time) as outcome variables. Sleepiness was assessed by the Karolinska Sleepiness Scale (KSS). A separate question was used to assess mental fatigue. Tests were conducted at the end of the operators’ shift on days 1, 3, and 6 of each shift block. KSS was also assessed at the start and end of all shifts. Data were analyzed using multilevel mixed-effects regression models with season, shift type (morning/night) and consecutive workday number as fixed effects. Results: Night shifts were linked to lower alertness, as well as higher sleepiness and fatigue, especially on the first night shift. Interaction effects indicated improved response speed, fewer lapses, and reduced sleepiness and fatigue over six-night shifts, with significant differences between night 1 and night 6. These patterns were similar for both seasons across all variables. However, PVT-tests showed that the overall contrast between morning and night shifts was only significant during the dark season (response speed: p < 0.0001, lapses: p≈0.005), but not during the light season. Neither sleepiness, nor fatigue, were significantly affected by seasons. Conclusion: These findings suggest that while night shifts generally impair alertness, as well as increase sleepiness and fatigue, workers may gradually adapt over consecutive shifts, as evidenced by improvements by the sixth night. The lack of significant seasonal effects on sleepiness and fatigue suggests that workers might adapt equally well to night shifts regardless of the photoperiod. However, the more pronounced differences in alertness between morning and night shifts during the dark season highlight the potential interplay between reduced daylight’s influence on circadian rhythms and adaptability to work night shifts.

• Moen, Line Victoria; Holme, Andreas Næss; Matre, Dagfinn & Haugen, Fred (2025). SEASONAL IMPACTS ON SLEEP IN ARCTIC SHIFT WORKERS: INSIGHTS FROM WEARABLE MONITORING. Full text in Research Archive Show summary

  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 cross-over 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 to 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 to 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 (if any) This research is supported by the RRESEARCH COUNCIL OF NORWAY; the PETROMAKS2 program ID# 326291

• Holme, Andreas Næss; Moen, Line Victoria; Matre, Dagfinn André & Haugen, Fred (2024). Impacts of night work and season on sleep duration in an Arctic work environment. Full text in Research Archive
• Moen, Line Victoria; Holme, Andreas Næss; Sallinen, Mikael; Phillips, Andrew J.K.; Nilsen, Kristian Bernhard & Lie, Jenny-Anne Sigstad [Show all 8 contributors for this article] (2024). Impacts of night work and season on sleepiness and vigilance in Arctic industrial workers. Full text in Research Archive
• Haugen, Fred; Matre, Dagfinn; Moen, Line Victoria; Holme, Andreas Næss & Lie, Jenny-Anne Sigstad (2024). Does the Arctic winter make you a night owl? A study of seasons’ effect on chronotype in shift workers. Full text in Research Archive
• Haugen, Fred; Holme, Andreas Næss; Matre, Dagfinn & Moen, Line Victoria (2026). «Polarnatt 1». Målinger av døgnrytmeforstyrrelser ved nattarbeid i Nordområdene og betydningen av mørketid og midnattssol. STAMI - Statens arbeidsmiljøinstitutt. Full text in Research Archive Show summary

  Målet med Polarnatt-1 er å bidra til redusert risiko for sikkerhetshendelser og langsiktige helseplager og sykdommer knyttet til nattarbeid og døgnrytmeforstyrrelser. Prosjektet har særlig søkelys på petroleumsvirksomhet i Nordområdene, og skal gi helt ny kunnskap om hvorvidt det bør tas spesielle hensyn til arbeidstidsordninger i ulike årstider. Prosjektet benyttet state-of-the-art, vitenskapelig validerte metoder for måling av døgnrytme, opprinnelig utviklet og validert i ikke-skiftpopulasjoner. Prosjektet anvendte disse metodene blant skiftarbeidere i et naturlig arbeidsmiljø i Nordområdene for å kvantifisere graden av døgnrytmeforstyrrelse etter påfølgende nattskift. Ettersom metodene ikke er spesifikt validert for skiftarbeidere, må resultatene tolkes med forbehold.

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