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  • 1.
    Persson, Roger
    et al.
    National Research Centre of Working Environment, Denmark.
    Helene Garde, Anne
    National Research Centre of Working Environment, Denmark.
    Marie Hansen, Ase
    National Research Centre of Working Environment, Denmark.
    Osterberg, Kai
    Lund University.
    Larsson, Britt
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Rehabilitation Medicine . Östergötlands Läns Landsting, Centre for Medicine, Pain and Rehabilitation Centre.
    Orbaek, Palle
    National Research Centre of Working Environment, Denmark.
    Karlson, Bjorn
    Lund University.
    Seasonal Variation in Human Salivary Cortisol Concentration2008In: Chronobiology International, ISSN 0742-0528, E-ISSN 1525-6073, Vol. 25, no 6, p. 923-937Article in journal (Refereed)
    Abstract [en]

    Measurement of cortisol concentration can contribute important information about an individuals ability to adjust to various environmental demands of both physical and psychosocial origin. However, one uncertainty that affects the possibilities of correctly interpreting and designing field studies is the lack of observations of the impact of seasonal changes on cortisol excretion. For this reason, the month-to-month changes in diurnal cortisol concentration, the awakening cortisol response (ACR), maximum morning concentration, and fall during the day were studied in a group of 24 healthy men and women 32 to 61 yrs of age engaged in active work. On one workday for 12 consecutive months, participants collected saliva at four time points for determination of cortisol: at awakening, +30min, +8h, and at 21:00h. Data were analyzed by a repeated measures design with month (12 levels) and time-of-day (4 levels) as categorical predictors. Cortisol concentrations were analyzed on a log scale. The diurnal pattern of cortisol was similar across months (interaction between month and time of day: p0.4). The main effects of month and time-of-day were statistically significant (p0.001). Highest concentrations were observed in February, March, and April, and lowest concentrations were observed in July and August. There were no statistically significant effects in any of the other measures, or between men and women. In conclusion, a seasonal variation in salivary cortisol concentrations was detected in an occupationally active population. Thus, seasonal variation needs to be taken into account when designing and evaluating field studies and interventions and when making comparisons across studies.

  • 2.
    van Leeuwen, Wessel M. A.
    et al.
    Stockholm University, Sweden .
    Kircher, Albert
    Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Dahlgren, Anna
    KTH Royal Institute of Technology, Sweden.
    Lutzhoft, Margareta
    Chalmers University of Technology, Gothenburg, Sweden.
    Barnett, Mike
    Southampton Solent University, UK.
    Kecklund, Goran
    Stockholm University, Sweden .
    Åkerstedt, Torbjörn
    Stockholm University, Sweden .
    Sleep, Sleepiness, and Neurobehavioral Performance While on Watch in a Simulated 4 Hours on/8 Hours off Maritime Watch System2013In: Chronobiology International, ISSN 0742-0528, E-ISSN 1525-6073, Vol. 30, no 9, p. 1108-1115Article in journal (Refereed)
    Abstract [en]

    Seafarer sleepiness jeopardizes safety at sea and has been documented as a direct or contributing factor in many maritime accidents. This study investigates sleep, sleepiness, and neurobehavioral performance in a simulated 4 h on/8 h off watch system as well as the effects of a single free watch disturbance, simulating a condition of overtime work, resulting in 16 h of work in a row and a missed sleep opportunity. Thirty bridge officers (age 30 +/- 6 yrs; 29 men) participated in bridge simulator trials on an identical 1-wk voyage in the North Sea and English Channel. The three watch teams started respectively with the 00-04, the 04-08, and the 08-12 watches. Participants rated their sleepiness every hour (Karolinska Sleepiness Scale [KSS]) and carried out a 5-min psychomotor vigilance test (PVT) test at the start and end of every watch. Polysomnography (PSG) was recorded during 6 watches in the first and the second half of the week. KSS was higher during the first (mean +/- SD: 4.0 +/- 0.2) compared with the second (3.3 +/- 0.2) watch of the day (p andlt; 0.001). In addition, it increased with hours on watch (p andlt; 0.001), peaking at the end of watch (4.1 +/- 0.2). The free watch disturbance increased KSS profoundly (p andlt; 0.001): from 4.2 +/- 0.2 to 6.5 +/- 0.3. PVT reaction times were slower during the first (290 +/- 6 ms) compared with the second (280 +/- 6 ms) watch of the day (p andlt; 0.001) as well as at the end of the watch (289 +/- 6 ms) compared with the start (281 +/- 6 ms; p = 0.001). The free watch disturbance increased reaction times (p andlt; 0.001) from 283 +/- 5 to 306 +/- 7 ms. Similar effects were observed for PVT lapses. One third of all participants slept during at least one of the PSG watches. Sleep on watch was most abundant in the team working 00-04 and it increased following the free watch disturbance. This study reveals that-within a 4 h on/8 h off shift system-subjective and objective sleepiness peak during the night and early morning watches, coinciding with a time frame in which relatively many maritime accidents occur. In addition, we showed that overtime work strongly increases sleepiness. Finally, a striking amount of participants fell asleep while on duty.

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