Torbjörn är professor emeritus vid Stressforskningsinstitutet, där han också ingår i en forskningsgrupp som fokuserar på stress, sömn och återhämtning och då särskilt på sömnens roll i trötthetsregleringen. Här ingår också preventiva insatser som t.ex. stresshantering, sömnrådgivning och vakenhetshöjande åtgärder. Torbjörn är också biträdande föreståndare för Stockholm Stress Center.
Fokus för min forskning är vad sömnkvalitet och sömnstörning egentligen är, liksom betydelsen av sömnkvalitet och sömnlängd för långsiktig funktionsförmåga, hälsa och mortalitet. Betydelsen av ålder, kön, stress, mm undersöks.
Ett annat fokus är effekterna av skiftarbete (oregelbundna arbetstider) på hälsa, funktionsförmåga och mortalitet.
De projekt som drivs är bl.a. följande
- Den rapporterade sömnlängdens och sömnkvalitetens betydelse för överlevnad och sjukdomar som demens, hjärt-/kärlsjukdom, diabetes, cancer, mm. Inflytande av ålder, pensionering, yrke, kön, mfl faktorer sambanden med dödlighet och ålder. Nära relaterat till ovanstående är att identifiera optimal sömnlängd (ur mortalitetsperspektiv) och vilka faktorer som påverkar. Är det lika stor risk att avlida med kort och lång sömn? Vad spelar helgsömnen för roll för mortaliteten?
- Den fysiologiska representationen av vad som utgör bra sömn. Här genomförs polysomnografi (PSG), dvs registrering av EEG, EOG (ögonrörelser) och EMG för att ge information om sömnstadier, uppvaknanden, sömneffektivitet, mm. Avsikten är att komma fram till vilka PSG-variabler som kan kopplas till rapporterad sömnstörning. Här ingår studier PSG-data från hundratals män och kvinnor, liksom av patienter under behandling. Viktiga delfrågor är könsskillnader, åldersskillnader, effekter av stress. Speciella frågeställningar rör om kvinnor verkligen sover objektivt sämre än män, om äldre verkligen är så objektivt sömnstörda som rapporteras, hur negativt stress är för sömnen, vad i den objektiva sömnen som förbättras med Kognitiv Beteendeterapeutisk behandling av insomni,
- Trötthet och sömnighet, båda ganska försummade forskningsområden, men som börjar komma i fokus. Frågeställningar rör: Hur farligt är sömnighet i trafiken? Hur förändras trötthet och sömnighet med ålder (det ser ut som om man blir mindre trött med ökad ålder, t.ex). Hur trötthetsframkallande är olika flygschemakarakteristika för piloter och kabinpersonal. Kan man förutsäga trötthet/sömnighet utifrån kunskap om arbetstider? Vilka faktorer driver trötthet/sömnighet (sömn, stress, fysiskt arbete, långa arbetstider, sjukdom)? Hur ser den trötta hjärnan ut, vilka hjärnstrukturer ändrar sin aktivitet? Vilka skiftschemakarakteristika (natt, långa pass, etc) utgör de stora problemen för dem som arbetar skift. Innebär Nattarbete en ökad risk att avlida och påverkas detta av rollen som arbetare/tjänsteman eller kön.
Många av projekten drivs i samarbete med andra forskare (Uppsala Universitet (Prof Eva Lindberg), Stockholms Universitet (Dr Johanna Schwarz, Prof Hui-Xin Wang, Prof Göran Kecklund), Karolinska institutet (Prof Viktor Kaldo, Doc Susanna Jernelöw, Dr Anna-Karin Hedström, Doc Ylva Trolle-Lageros), Finska arbetshälsoinstitutet (Prof Mikael Sallinen), Universitetet i Milano/Bicocca (Prof Rino Bellocco), Holländska flygforskningsinstitutet (NLR) (Dr Henk van Dijk), Tyska flyg- och rymdforskningsinstitutet (Dr Daniel Aeschbach)
I urval från Stockholms universitets publikationsdatabas
Total workload and recovery in relation to worktime reduction – a randomized controlled intervention study with time-use data
Helena Schiller (et al.).
Objectives: A 25% reduction of weekly work hours for full-time employees has been shown to improve sleep and alertness and reduce stress during both workdays and days off. The aim of the present study was to investigate how employees use their time during such an intervention: does total workload (paid and non-paid work) decrease, and recovery time increase, when work hours are reduced?
Methods: Full-time employees within the public sector (N=636; 75% women) were randomized into intervention group and control group. The intervention group (N=370) reduced worktime to 75% with preserved salary during 18 months. Data were collected at baseline, after 9 months and 18 months. Time-use was reported every half hour daily between 06 and 01 a.m. during one week at each data collection. Data were analyzed with multilevel mixed modeling.
Results: Compared to the control group, the intervention group increased the time spent on domestic work and relaxing hobby activities during workdays when worktime was reduced (p≤0.001). On days off, more time was spent in free-time activities (p=0.003). Total workload decreased (-65 minutes) and time spent in recovery activities increased on workdays (+53 minutes). The pattern of findings was similar in subgroups defined by gender, family status and job situation.
Conclusions: A worktime reduction of 25% for full-time workers resulted in decreased total workload and an increase of time spent in recovery activities, which is in line with the suggestion that worktime reduction may be beneficial for long-term health and stress.
Aging and the Change in Fatigue and Sleep - A Longitudinal Study Across 8 Years in Three Age Groups
2018. Torbjörn Åkerstedt (et al.). Frontiers in Psychology 9Artikel
Fatigue is prevalent in the population and usually linked to sleep problems, and both are related to age. However, previous studies have been cross-sectional. The purpose of the present study was to investigate the trajectories of sleep and fatigue across 8 years of aging in a large group (N > 8.000) of individuals. A second purpose was to investigate whether fatigue trajectories would differ between age groups, and whether different trajectories of fatigue would be reflected in a corresponding difference in trajectories for sleep variables. Results from mixed model analyses showed that fatigue decreased across 8 years in all age groups, while sleep problems increased, non-restorative sleep decreased, weekend sleep duration decreased, and weekday sleep duration showed different patterns depending on age. Furthermore, the larger the decrease in fatigue, the larger was the increase in sleep duration across years, the lower was the increase of sleep problems, and the larger was the decrease of non-restorative sleep. The results suggest that aging has positive effects on fatigue and sleep and that these changes are linked.
Are professional drivers less sleepy than non-professional drivers?
2018. Anna Anund (et al.). Scandinavian Journal of Work, Environment and Health 44 (1), 88-95Artikel
Objective It is generally believed that professional drivers can manage quite severe fatigue before routine driving performance is affected. In addition, there are results indicating that professional drivers can adapt to prolonged night shifts and may be able to learn to drive without decreased performance under high levels of sleepiness. However, very little research has been conducted to compare professionals and non-professionals when controlling for time driven and time of day.
Method The aim of this study was to use a driving simulator to investigate whether professional drivers are more resistant to sleep deprivation than non-professional drivers. Differences in the development of sleepiness (self-reported, physiological and behavioral) during driving was investigated in 11 young professional and 15 non-professional drivers.
Results Professional drivers self-reported significantly lower sleepiness while driving a simulator than nonprofessional drivers. In contradiction, they showed longer blink durations and more line crossings, both of which are indicators of sleepiness. They also drove faster. The reason for the discrepancy in the relation between the different sleepiness indicators for the two groups could be due to more experience to sleepiness among the professional drivers or possibly to the faster speed, which might unconsciously have been used by the professionals to try to counteract sleepiness.
Conclusion Professional drivers self-reported significantly lower sleepiness while driving a simulator than non-professional drivers. However, they showed longer blink durations and more line crossings, both of which are indicators of sleepiness, and they drove faster.
Criteria for self-reported quantitative sleep characteristics of individuals who sought medical help for disturbed sleep - a survey of a representative sample of the Swedish population
2018. Anna Miley-Åkerstedt, Jerker Hetta, Torbjorn Åkerstedt. Nature and Science of Sleep 10, 295-301Artikel
Background: The public often seeks rule-of-thumb criteria for good or poor sleep, with a particular emphasis on sleep duration, sleep latency, and the number of awakenings each night. However, very few criteria are available. Aim: The present study sought to identify such criteria. Methods: Whether or not a person has sought medical help for sleep problems was selected as an indicator of poor sleep. The group that was studied constituted a representative sample of the general Swedish population (N=1,128), with a response rate of 72.8%. Results: Logistic regression analysis, with an adjustment for age and gender, showed an increased OR for a weekday sleep duration of <= 6 hour, (OR >2, and for <5 hour: OR >6). For weekend sleep, the value was <= 6 hour (OR >2). For awakenings per night, the critical value was >= 2 (OR >2, and for awakenings: OR >9), and for a sleep latency the critical value was >= 30 minutes (OR >2, and for >= 45 minutes: OR >6). Adding difficulties falling asleep and early morning awakening (considered qualitative because of the reflected difficulty), led to the elimination of all the quantitative variables, except for the number of awakenings. The addition of negative effects on daytime functioning and sleep being a big problem resulted in the elimination of all the other predictors except age. Conclusion: It was concluded that weekday sleep <= 6 hour, >= 2 awakenings/night, and a sleep latency of >= 30 minutes, can function as criteria for poor sleep, but that qualitative sleep variables take over the role of quantitative ones, probably because they represent the integration of quantitative indicators of sleep.
Does sleep deprivation increase the vulnerability to acute psychosocial stress in young and older adults?
2018. Johanna Schwarz (et al.). Psychoneuroendocrinology 96, 155-165Artikel
Sleep loss and psychosocial stress often co-occur in today’s society, but there is limited knowledge on the combined effects. Therefore, this experimental study investigated whether one night of sleep deprivation affects the response to a psychosocial challenge. A second aim was to examine if older adults, who may be less affected by both sleep deprivation and stress, react differently than young adults. 124 young (18–30 years) and 94 older (60–72 years) healthy adults participated in one of four conditions: i. normal night sleep & Placebo-Trier Social Stress Test (TSST), ii. normal night sleep & Trier Social Stress Test, iii. sleep deprivation & Placebo-TSST, iv. sleep deprivation & TSST. Subjective stress ratings, heart rate variability (HRV), salivary alpha amylase (sAA) and cortisol were measured throughout the protocol. At the baseline pre-stress measurement, salivary cortisol and subjective stress values were higher in sleep deprived than in rested participants. However, the reactivity to and recovery from the TSST was not significantly different after sleep deprivation for any of the outcome measures. Older adults showed higher subjective stress, higher sAA and lower HRV at baseline, indicating increased basal autonomic activity. Cortisol trajectories and HRV slightly differed in older adults compared with younger adults (regardless of the TSST). Moreover, age did not moderate the effect of sleep deprivation. Taken together, the results show increased stress levels after sleep deprivation, but do not confirm the assumption that one night of sleep deprivation increases the responsivity to an acute psychosocial challenge.
Gray Matter Volume Correlates of Sleepiness
2020. Torbjörn Åkerstedt (et al.). Nature and Science of Sleep 12, 289-298Artikel
Background: Subjectively experienced sleepiness is a problem in society, possibly linked with gray matter (GM) volume. Given a different sleep pattern, aging may affect such associations, possibly due to shrinking brain volume.
Purpose: The purpose of the present study was to investigate the association between subjectively rated sleepiness and GM volume in thalamus, insula, hippocampus, and orbitofrontal cortex of young and older adults, after a normal night’s sleep.
Methods: Eighty-four healthy individuals participated (46 aged 20– 30 years, and 38 aged 65– 75 years). Morphological brain data were collected in a 3T magnetic resonance imaging (MRI) scanner. Sleepiness was rated multiple times during the imaging sessions.
Results: In older, relative to younger, adults, clusters within bilateral mid-anterior insular cortex and right thalamus were negatively associated with sleepiness. Adjustment for the immediately preceding total sleep time eliminated the significant associations.
Conclusion: Self-rated momentary sleepiness in a monotonous situation appears to be negatively associated with GM volume in clusters within both thalamus and insula in older individuals, and total sleep time seems to play a role in this association. Possibly, this suggests that larger GM volume in these clusters may be protective against sleepiness in older individuals. This notion needs confirmation in further studies.
Reciprocal relations between work stress and insomnia symptoms
2020. Johanna Garefelt (et al.). Journal of Sleep Research 29 (2)Artikel
Work stress and poor sleep are closely related in cross-sectional data, but evidence from prospective data is limited. We analysed how perceived stress and work stressors (work demands, decision authority and workplace social support) are related to key dimensions of insomnia over time, using structural equation modelling. Biennial measurements from a large sample of the working population in Sweden enabled us to analyse both the relationship from stress to sleep as well as that from sleep to stress. Overall, we found reciprocal relations between insomnia and all four stress measures. However, looking at the relation between each dimension of insomnia and each stress measure, there were some differences in direction of effects. In the direction from stress to sleep, all work stressors as well as perceived stress predicted both difficulties initiating sleep and difficulties maintaining sleep. The same was found for non-restorative sleep, with the exception for decision authority. In the opposite direction, difficulties maintaining sleep predicted increased levels of work demands and perceived stress. Difficulties initiating sleep stood out among the insomnia symptoms as not predicting any of the stress measures, while non-restorative sleep was the only symptom predicting all stress measures. The results advance the understanding of the stress-sleep relationship and indicate a potential vicious circle between insomnia and perceived stress as well as work stressors, suggesting that the workplace could be an arena for interventions to alleviate insomnia.
Relationship between sleep characteristics and markers of inflammation in Swedish women from the general population
2020. Francesca Ghilotti (et al.). Journal of Sleep ResearchArtikel
Systemic inflammation is thought to mediate the link between sleep and cardiovascular outcomes, but previous studies on sleep habits and inflammation markers have found inconsistent results. This study investigated the relationship between sleep characteristics and C-reactive protein (CRP), interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF alpha). A representative sample of 319 Swedish women was randomly selected from the general population for in-home polysomnography, sleep questionnaire and blood samples. As variables were highly correlated, principal component analysis was used to reduce the number of original variables. Linear regression with log-transformation of the outcomes (lnCRP, lnIL-6 and lnTNF alpha) and quantile regression were fitted to estimate cross-sectional relationships. Multivariable linear regression models suggested a significant association of insomnia symptoms (self-reported) with higher lnCRP levels (beta = 0.11; 95% confidence interval [CI] = 0.02; 0.21), but not with lnIL-6 and lnTNF alpha. From quantile regression analysis we found that a high non-restorative index (subjective) and insomnia symptoms (self-reported) were associated with higher values of CRP, especially in the highest quantiles of the CRP distribution (90th percentile: beta = 0.71; 95% CI = 0.17; 1.24. beta = 1.23; 95% CI = 0.44; 2.02, respectively). Additionally, higher amounts of rapid eye movement (REM) sleep were associated with lower CRP values (90th percentile: beta = -0.80; 95% CI = -0.14; -1.46). In conclusion, sleep disturbances (self-reported), specifically difficulties maintaining sleep and early morning awakenings, but not sleep duration (neither subjective nor objective), were associated with higher CRP levels. No association was found with IL-6 or TNF alpha. Elevated REM sleep was associated with lower CRP levels. The results suggest that inflammation might be an intermediate mechanism linking sleep and health in women.
Short- and long-term mortality following hypnotic use
2020. Anna Karin Hedström (et al.). Journal of Sleep ResearchArtikel
Potential long-term consequences of hypnotics remain controversial. We used the prospective Swedish National March Cohort, a study based on 41,695 participants with a mean follow-up duration of 18.9 years. Logistic regression models and Cox proportional hazards models with attained age as timescale were used to assess associations of hypnotic use with short- and long-term mortality. The proportion of subjects who initiated or discontinued hypnotic use during follow-up was substantial. All groups of hypnotics were associated with increased mortality within 2 years after a first prescription, with an overall OR of 2.38 (95% CI, 2.13-2.66). The association was more pronounced among subjects younger than 60 years (OR, 6.16; 95% CI, 3.98-9.52). There was no association between hypnotic use and long-term mortality. The association between hypnotic use and increased mortality was thus restricted to a relatively short period after treatment initiation, and may be explained in terms of confounding by indication.
Association Between Insomnia And Mortality Is Only Evident Among Long Sleepers
2019. Anna Karin Hedström (et al.). Nature and Science of Sleep 11, 333-342Artikel
Background: Previous studies investigating the relationship between insomnia and mortality have been inconsistent. Purpose: We aimed to assess whether nocturnal insomnia symptoms and non-restorative sleep are associated with all-cause mortality and whether they modify the associations between short and long sleep duration and all-cause mortality. Patients and methods: The present report is based on a prospective cohort study of 39,139 participants with a mean follow-up time of 19.6 years. Cox proportional hazard models with attained age as timescale were used to estimate overall mortality hazard ratios (HRs) with 95% confidence intervals (CI) for different categories of sleep duration and insomnia symptoms. Results: Both difficulty initiating sleep and daytime sleepiness were independently associated with increased mortality among those with sleep duration of 9 hrs or more (HR 1.51, 95% CI 1.11-2.07 and HR 1.37, 95% CI 1.03-1.82). Mortality increased with increasing severity of difficulties initiating sleep (p for trend 0.04) and daytime sleepiness (p for trend 0.01) among the long sleepers. None of the insomnia symptoms were associated with mortality among those who reported sleep duration of 8 hrs or less. Conclusion: Long sleep in combination with difficulties initiating sleep and daytime sleepiness, possibly due to psychiatric or physical disorders, was thus associated with increased mortality, whereas long sleep without difficulties falling asleep or daytime sleepiness was not associated with mortality. Our study emphasizes the need to take nocturnal insomnia symptoms and daytime sleepiness into consideration when assessing the influence of sleep duration on mortality. Additional research is needed to elucidate the relationship between long sleep, insomnia and related psychiatric and physical disorders.
Psychosocial work demands and physical workload decrease with ageing in blue-collar and white-collar workers
2019. Torbjörn Åkerstedt (et al.). BMJ Open 9 (9)Artikel
Objectives Psychosocial work demands and physical workload are important causes of ill health. The dramatic demographic changes in society make it important to understand if such factors change with ageing, but this is presently not known. The purpose of the present study was to investigate whether psychosocial work demands and physical workload change across 8years of ageing, whether occupational groups show different trajectories of change and if such trajectories are reflected in sleep or fatigue. Methods A cohort of 5377 participants (mean age: 47.611.6 (SD) years, 43.2% males, 40.2% blue-collar workers) was measured through self-report in five biannual waves across 8 years. Mixed model regression analyses was used to investigate change across ageing. Results Psychosocial work demands decreased significantly across 8 years (Coeff: -0.016 +/- 0.001), with the strongest decrease in the high white-collar group (Coeff=-0.031 +/- 0.003) and the oldest group. Physical workload also decreased significantly (Coeff=-0.032 +/- 0.002), particularly in the blue-collar group (Coeff=-0.050 +/- 0.004) and in the oldest group. Fatigue decreased, and sleep problems increased with ageing, but with similar slopes in the occupational groups. All effect sizes were small, but extrapolation suggests substantial decreases across a working life career. Conclusions The decrease in psychosocial work demands and physical workload suggests that the burden of work becomes somewhat lighter over 8 years. The mechanism could be 'pure' ageing and/or increased experience or related factors. The gradual improvement in the work situation should be considered in the discussion of the place of older individuals in the labour market, and of a suitable age for retirement. The results also mean that prospective studies of work and health need to consider the improvement in working life with ageing.
Shift Work - Sleepiness and Sleep in Transport
2019. Torbjörn Åkerstedt. Sleep Medicine Clinics 14 (4), 413-421Artikel
Driving a vehicle during a night shift increases the accident risk and incidents of falling asleep at the wheel. Individuals having worked a night shift (in any type of occupation) run a similar risk when commuting home from a night shift. Early starts of driving may increase risk. Detailed field studies of sleepiness indicate high levels of sleepiness during late night driving. The mechanism includes exposure to the circadian trough of alertness during work and sleep loss. High levels of sleepiness and sleep loss associated with night and early morning work define the diagnosis of shift work disorder.
Short sleep-poor sleep? A polysomnographic study in a large population-based sample of women
2019. Torbjorn Åkerstedt (et al.). Journal of Sleep Research 28 (4)Artikel
There is a lack of studies on the association between total sleep time (TST) and other polysomnographical parameters. A key question is whether a short sleep is an expression of habitual short sleep, or whether it reflects temporary impairment. The purpose of the present study was to investigate the association between TST and amount of sleep stages and sleep continuity measures, in a large population-based sample of women (n = 385), sleeping at home in a normal daily life setting. The results show that sleep efficiency, N1 (min), N2 (min), REM (min), REM% and proportion of long sleep segments, increased with increasing TST, whereas the number of awakenings/hr, the number of arousals/hr, N1% and REM intensity decreased. In addition, longer sleep was more associated with TST being perceived as of usual duration and with better subjective sleep quality. TST was not associated with habitual reported sleep duration. It was concluded that short TST of a recorded sleep in a real-life context may be an indicator of poor objective sleep quality for that particular sleep episode. Because individuals clearly perceived this reduction, it appears that self-reports of poor sleep quality often may be seen as indicators of poor sleep quality. It is also concluded that PSG-recorded sleep duration does not reflect habitual reported sleep duration in the present real-life context.
Sleep duration and mortality - Does weekend sleep matter?
2019. Torbjörn Åkerstedt (et al.). Journal of Sleep Research 28 (1)Artikel
Previous studies have found a U-shaped relationship between mortality and (weekday) sleep duration. We here address the association of both weekday and weekend sleep duration with overall mortality. A cohort of 43,880 subjects was followed for 13 years through record-linkages. Cox proportional hazards regression models with attained age as time-scale were fitted to estimate multivariable-adjusted hazard ratios and 95% confidence intervals for mortality; stratified analyses on age (<65 years, >= 65 years) were conducted. Among individuals <65 years old, short sleep (<= 5 hr) during weekends at baseline was associated with a 52% higher mortality rate (hazard ratios 1.52; 95% confidence intervals 1.15-2.02) compared with the reference group (7 hr), while no association was observed for long (>= 9 hr) weekend sleep. When, instead, different combinations of weekday and weekend sleep durations were analysed, we observed a detrimental association with consistently sleeping <= 5 hr (hazard ratios 1.65; 95% confidence intervals 1.22-2.23) or >= 8 hr (hazard ratios 1.25; 95% confidence intervals 1.05-1.50), compared with consistently sleeping 6-7 hr per day (reference). The mortality rate among participants with short sleep during weekdays, but long sleep during weekends, did not differ from the rate of the reference group. Among individuals >= 65 years old, no association between weekend sleep or weekday/weekend sleep durations and mortality was observed. In conclusion, short, but not long, weekend sleep was associated with an increased mortality in subjects <65 years. In the same age group, short sleep (or long sleep) on both weekdays and weekend showed increased mortality. Possibly, long weekend sleep may compensate for short weekday sleep.
Effects of late-night short-sleep on in-home polysomnography
2018. Torbjörn Åkerstedt (et al.). Journal of Sleep Research 27 (4)Artikel
Bedtime is frequently delayed by many factors in life, and a homeostatic response to the delay may compensate partly for increased time awake and shortened sleep. Because sleep becomes shorter with age and women complain of disturbed sleep more often than men, age and sex differences in the homeostatic response to a delayed bedtime may modify the homeostatic response. The purpose of the present study was to investigate the effect of late-night short-sleep (3 h with awakening at about 07:00 hours) on in-home recorded sleep in men and women in two age groups (20-30 and 65-75 years). Results (N = 59) showed that late-night short-sleep was associated with an increase in percentage of N3 sleep and a decrease in percentage of rapid eye movement sleep, as well as decreases in several measures of sleep discontinuity and rapid eye movement density. Men showed a smaller decrease in percentage of rapid eye movement sleep than women in response to late-night short-sleep, as did older individuals of both sexes compared with younger. Older men showed a weaker percentage of N3 sleep in response to late-night short-sleep than younger men. In general, men showed a greater percentage of rapid eye movement sleep and a lower percentage of N3 sleep than women, and older individuals showed a lower percentage of N3 sleep than younger. In particular, older men showed very low levels of percentage of N3 sleep. We conclude that older males show less of a homeostatic response to late-night short-sleep. This may be an indication of impaired capacity for recovery in older men. Future studies should investigate if this pattern can be linked to gender-associated differences in morbidity and mortality.
Are long-haul truck drivers unusually alert? A comparison with long-haul airline pilots
2020. Mikael Sallinen (et al.). Accident Analysis and Prevention 137Artikel
Background: Recent studies suggest heavy vehicle drivers self-estimate their sleepiness unexpectedly low during night duties. The present study compared sleepiness ratings of long-haul truck drivers with those of long-haul airline pilots during night and non-night duties. In addition, the correspondence between self-rated manifest and predicted latent sleepiness was examined in the two groups. Methods: Twenty-two drivers and 33 pilots participated. Their working hours, sleep, on-duty sleepiness, and use of sleepiness countermeasures were measured in naturalistic conditions. Predictions of latent sleepiness were based on the measurements of working hours and sleep using the Sleep/Wake Predictor modelling tool. Results: Drivers rated lower levels of sleepiness than pilots during both duty types, though predicted latent sleepiness levels were very similar among the two groups. Neither the results of sleep nor those of sleepiness countermeasures explained the difference in self-rated sleepiness. Discussion: The results raise the possibility that long-haul truck drivers are actually sleepier than they report, and thus are at an increased risk for not responding to sleepiness in a timely manner. A potential explanation for this behavior is lack of education and training on sleepiness among truck drivers as compared with airline pilots. Alternatively, long-haul truck drivers may be exceptionally tolerant to soporific working conditions. The first reported results do not, however, support this hypothesis.