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
Shiftworkers’ attitude to their work hours, positive or negative, and why?
2022. Torbjörn Åkerstedt, Mikael Sallinen, Göran Kecklund. International Archives of Occupational and Environmental HealthArtikel
Objective Shift work is associated with impaired health and safety but there is a lack of systematic knowledge of shift workers attitude to their shift systems. This may be important for the ability to retain valuable personnel in the company/organization, and to attract new employees. The purpose of the present study was to investigate: the prevalence of shift characteristics (nights, long shifts, short rest, etc.) in traditional shift systems, the workers’ attitude to their shift systems, if combinations of problematic shift characteristics are associated with the workers’ attitude, and if work stress and poor sleep, fatigue, or social difficulties are associated with attitudes to shift systems.
Methods A representative sample of 3,500 individuals with non-day work in the general population of Sweden were asked to participate in the study. A total of 1965 workers remained after drop-outs. The material was analyzed by Chi2 analysis and hierarchical multiple regression.
Results The results showed that traditional shift systems included many more shift characteristics than those constituting the core of the systems. All included day work, for example. 90.2% of those with roster work had shifts > 10 h at least once a month. 66.9% of those with roster work without nights had < 11 h rest between shifts at least once a month. Less than 25% of the respondents had a rather or very negative attitude to their shift system, with the lowest level for those who work either fixed days or nights (7.6 and 5.7%, respectively) and highest for three-shift work (21.2%) and roster work without night work (24.4%). Shiftwork or roster work with nights had highest levels (> 50%) of sleep problems and fatigue. The difference across shift systems was significant at p < .001 in all cases. Combinations of the most problematic shift characteristics were associated with some increase in negative attitude to the shift schedule. Among schedule characteristics, only long weeks turned out significant in the multivariable regression. The strongest predictor of negative attitude to work hours were social difficulties due to work schedule [ß = 4.98 (95% Confidence interval (Ci) = 3.41, 7.27; p < .001], fatigue caused by schedule (ß = 3.20 Ci = 2.03, 5.05; p < .001), sleep problems caused by schedule (ß = 2.10 Ci = 1.46, 3.01; p = .01), and stressful work (ß = 1.52 Ci = 1.10, 2.11; p < .05).
Conclusion It was concluded that shift systems often included many different shift characteristics, that night shift systems had a large proportion of long shifts, and that split shifts mainly occurred in roster day work. Furthermore, it was concluded that the attitude to the worker’s present shift systems seems to be positive for the majority, with the highest level for those who work either fixed days or nights, compared to those who work alternating shifts (including night shifts). Negative attitude to shift systems was more linked to social difficulties, fatigue or sleep problems due to the shift schedule, than to schedule characteristics per se.
Acute and cumulative effects of scheduling on aircrew fatigue in ultra-short-haul operations
2021. Torbjörn Åkerstedt (et al.). Journal of Sleep Research 30 (5)Artikel
Aircrew fatigue constitutes a safety hazard in aviation, which authorities attempt to mitigate through flight time limitations. Some gaps in knowledge exist, however. The purpose of the present study was to investigate the associations of schedule characteristics with fatigue and amount of sleep in the acute 24-h window, and as cumulative effects across the 7-day work period. One hundred and six aircrew (14% cabin crew) participated. They rated fatigue on the Karolinska Sleepiness Scale (KSS) three times per flight day for four 7-day work periods, with up to 7 days off between work periods. Mixed model regression was applied to the data. In the multivariable model, more sleep was associated with lower fatigue (p = .000)), corresponding to 0.26 KSS units less per hour of sleep. Very early, early and late duty types, as well as duty time, were associated with higher fatigue. For the 7-day work period, accumulation of very early duties and longer duty time were associated with increased fatigue, and more accumulated sleep was associated with lower fatigue in the adjusted model (0.08 KSS units per hour of sleep) (p = .000). Accumulated duty time was not significant when analysed as a single variable, but became so after adjustment for sleep. The results suggest that sleep, duty time and early starts are important predictors of fatigue in the 24-h window and that the number of very early starts and short sleep have cumulative effects on fatigue across a 7-day work period.
Cortical thickness and resting-state cardiac function across the lifespan
2021. Julian Koenig (et al.). Psychophysiology 58 (7)Artikel
Understanding the association between autonomic nervous system [ANS] function and brain morphology across the lifespan provides important insights into neurovisceral mechanisms underlying health and disease. Resting-state ANS activity, indexed by measures of heart rate [HR] and its variability [HRV] has been associated with brain morphology, particularly cortical thickness [CT]. While findings have been mixed regarding the anatomical distribution and direction of the associations, these inconsistencies may be due to sex and age differences in HR/HRV and CT. Previous studies have been limited by small sample sizes, which impede the assessment of sex differences and aging effects on the association between ANS function and CT. To overcome these limitations, 20 groups worldwide contributed data collected under similar protocols of CT assessment and HR/HRV recording to be pooled in a mega-analysis (N = 1,218 (50.5% female), mean age 36.7 years (range: 12–87)). Findings suggest a decline in HRV as well as CT with increasing age. CT, particularly in the orbitofrontal cortex, explained additional variance in HRV, beyond the effects of aging. This pattern of results may suggest that the decline in HRV with increasing age is related to a decline in orbitofrontal CT. These effects were independent of sex and specific to HRV; with no significant association between CT and HR. Greater CT across the adult lifespan may be vital for the maintenance of healthy cardiac regulation via the ANS—or greater cardiac vagal activity as indirectly reflected in HRV may slow brain atrophy. Findings reveal an important association between CT and cardiac parasympathetic activity with implications for healthy aging and longevity that should be studied further in longitudinal research.
Effects of alcohol consumption and smoking on risk for RA
2021. Louise Hedenstierna (et al.). RMD Open 7 (1)Artikel
Objective Several, but not all studies, have shown a dose-dependent inverse association with alcohol consumption and rheumatoid arthritis (RA), whereas smoking is an established risk factor for RA. We aimed to study the association between alcohol consumption and RA incidence and investigate a potential interaction between alcohol and smoking habits, regarding RA incidence.
Methods We used a prospective cohort study, based on 41 068 participants with detailed assessment of alcohol intake, smoking and potential confounders at baseline in 1997. We ascertained a total of 577 incident cases of RA during a mean of 17.7 years of follow-up through linkage to nationwide and essentially complete databases. Multivariate Cox proportional hazards models were used to estimate HR with 95% CI. Interaction on the additive scale between alcohol and smoking was estimated by calculating the attributable proportion due to interaction (AP).
Results Overall, alcohol consumption was associated with a 30% reduced incidence of RA (HR 0.69, 95% CI 0.55 to 0.86) with a dose-response relationship (p value for trend <0.001) which remained significant after stratification by age and smoking habits. The positive association between smoking and RA incidence was reduced with increasing alcohol consumption (p value for trend <0.001). A synergistic effect was observed between alcohol and smoking (AP 0.40, 95% CI 0.15 to 0.64), indicating that 40% of the cases among the double exposed are due to the interaction per se.
Conclusions Our findings suggest an inverse association between alcohol consumption and RA incidence, and a synergistic effect between alcohol and smoking.
Insomnia in the context of short sleep increases suicide risk
2021. Anna Karin Hedström (et al.). Sleep 44 (4)Artikel
Study objectives: The relationship between insomnia and suicide risk is not completely understood. We aimed to investigate the influence of insomnia on suicide risk, taking both sleep duration and depression into consideration.
Methods: The present study is based on a Swedish prospective cohort study of 38,786 participants with a mean follow-up time of 19.2 years. Cox proportional hazards models with attained age as time-scale were used to estimate hazard ratios (HRs) of death by suicide with 95% confidence intervals (CI) for participants categorized by frequency of insomnia symptoms. Causal mediation analysis was performed to assess to what extent the relationship between insomnia and suicide risk is mediated by depression.
Results: Insomnia was only associated with suicide risk among short sleepers, whereas no significant association was observed among those who slept 7 h/night or more. The total effect of insomnia in the context of short sleep on suicide risk, expressed on the HR scale, was 2.85 (95% CI 1.42-5.74). The direct effect was 2.25 (95% CI 1.12-4.54) and the indirect effect, mediated by depression, was 1.27 (95% CI 1.05-1.53). Of the total effect, 32% was mediated by depression. The association between insomnia and suicide risk became more pronounced with decreasing depressive symptoms (p value for trend <0.05).
Conclusions: Insomnia in the context of short sleep increases suicide risk, both directly and indirectly by affecting the risk of depression. Abnormalities of sleep duration and insomnia symptoms should be evaluated when assessing suicide risk.
Self-reported reasons for on-duty sleepiness among commercial airline pilots
2021. Mikael Sallinen (et al.). Chronobiology International 38 (9), 1308-1318Artikel
Experimental and epidemiological research has shown that human sleepiness is determined especially by the circadian and homeostatic processes. The present field study examined which work-related factors airline pilots perceive as causing on-duty sleepiness during short-haul and long-haul flights. In addition, the association between the perceived reasons for sleepiness and actual sleepiness levels was examined, as well as the association between reporting inadequate sleep causing sleepiness and actual sleep-wake history. The study sample consisted of 29 long-haul (LH) pilots, 28 short-haul (SH) pilots, and 29 mixed fleet pilots (flying both SH and LH flights), each of whom participated in a 2-month field measurement period, yielding a total of 765 SH and 494 LH flight duty periods (FDPs) for analyses (FDP, a period between the start of a duty and the end of the last flight of that duty). The self-reports of sleepiness inducers were collected at the end of each FDP by an electronic select menu. On-duty sleepiness was rated at each flight phase by the Karolinska Sleepiness Scale (KSS). The sleep-wake data was collected by a diary and actigraph. The results showed that “FDP timing” and “inadequate sleep” were the most frequently reported reasons for on-duty sleepiness out of the seven options provided, regardless of FDP type (SH, LH). Reporting these reasons significantly increased the odds of increased on-duty sleepiness (KSS ≥ 7), except for reporting “inadequate sleep” during LH FDPs. Reporting “inadequate sleep” was also associated with increased odds of a reduced sleep-wake ratio (total sleep time/amount of wakefulness ≤ 0.33). Both “FDP timing” and “inadequate sleep” were most frequently reported during early morning and night FDPs, whereas the other options showed no such phenomenon. The present study suggests that airline pilots’ perceptions of work-related factors that make them sleepy at work are in line with the previous experimental and epidemiological studies of sleepiness regulation.
Sleep duration and mortality - Influence of age and occupational group in retired individuals
2021. Torbjörn Åkerstedt, Jurgita Narusyte, Pia Svedberg. Sleep Medicine 80, 199-203Artikel
The importance of sleep duration for health or mortality attracts much public attention. Prior work indicates that both long and short sleep duration predicts mortality, with optimal sleep duration (lowest risk) at 7 h. However, we believe this may differ between subgroups. This may be the case with, for example, age groups (due to aging), or blue-collar and white-collar worker (due to work exposure). It is also likely that retirement, which permits extension of the time in bed, may confound analyses. The purpose of the present study was to investigate how occupational group (blue-collar/white-collar worker) and age influence the pattern of association between sleep duration and mortality in retired individuals. Retired individuals were selected since it was hypothesized that effects of occupation may accumulate over years and since the transition into retirement may be a confounder. We used a sample of 14 000 individuals from the Swedish Twin Registry, which had provided data on sleep duration and a number of covariates. Cox proportional hazards analysis was applied to data. The results show that occupational group did not influence the association, but showed significant hazard ratios (HR) for long (>= 9.5 h) and short (<6.5 h) sleep in both groups (HR > 1.35), with optimal sleep duration (lowest HR) with a wide span (6.5-9.5 h). Age groups in tertiles also showed significant U-shapes, with a wide span (6.5-9.5 h) for the younger 2/3 (54-74 years), but a weaker pattern for the oldest third (>= 75 years), for which optimal sleep fell in the 6.5-7.5 h interval. It was concluded that occupational group does not influence the association between sleep duration and mortality in retired individuals, but that age does.
Sleep duration and mortality, influence of age, retirement, and occupational group
2021. Torbjörn Åkerstedt (et al.). Journal of Sleep ResearchArtikel
Previous work has shown that both long and short sleep duration is associated with increased mortality, with lowest risk around 7 hr. This has had widespread impact on views on the optimal sleep duration. However, age, being employed/retired, and blue-/white-collar status, may influence the time available for sleep and thus, confound the association. We investigated the role of these factors on the association between sleep duration and mortality. We used employed and retired participants (N = 25,430) from the Swedish National March Cohort and Cox proportional hazards regression to model the shape of the association. We found a significant U-shaped association in a multivariable model with a hazard ratio (HR) of 1.24 (95% confidence interval [CI] 1.10, 1.39) for <5-hr sleep duration, and a HR of 1.30 (95% CI 1.12, 1.51) for >= 9-hr sleep duration, with the lowest HR for 7 hr, but with a span of low HRs from 5 to 8 hr. Unadjusted values showed a pronounced U-shape. Adjusting for age accounted for most of the attenuation in the multivariable model. Stratification into five age groups showed a significant U-shape only in those aged >60.3 years at baseline. The shape of the association did not differ between blue-/white-collar workers, nor between employed and retired groups. We conclude that the U-shaped association between sleep duration and mortality is present only in older individuals.
The mediating role of insomnia severity in internet-based cognitive behavioral therapy for chronic stress
2021. Elin Lindsäter (et al.). Behaviour Research and Therapy 136Artikel
The aim of this study was to investigate insomnia symptom severity as a putative mediator of treatment response in therapist-guided internet-based cognitive behavioral therapy (ICBT) for chronic stress, using data from a randomized controlled trial. Participants (N = 100) were randomized to 12 weeks of ICBT or to a waitlist control condition (WLC). Insomnia severity was assessed weekly with the Insomnia Severity Index (ISI), as were the stress-related outcomes the Perceived Stress Scale (PSS) and the Shirom-Melamed Burnout Questionnaire (SMBQ). Latent growth models indicated that ICBT (vs. WLC) predicted a decrease in insomnia severity (alpha-path), and that growth in insomnia severity was predictive of growth in perceived stress and exhaustion (beta-paths). Most importantly, there were also significant indirect effects (alpha beta products) such that the beneficial effects of ICBT on perceived stress and exhaustion were mediated by a reduction in insomnia symptom severity (PSS: alpha beta =-0.44, 95% CI [-0.92,-0.14]; SMBQ: alpha beta =-0.08, 95% CI [-0.15, 0.04]). Explorative analysis of moderated mediation showed that more severe insomnia symptoms at baseline were associated with larger mediated effects. We conclude that reducing insomnia severity could be of importance for achieving successful treatment outcomes in ICBT for chronic stress.
The relationship between nightmares, depression and suicide
2021. Anna Karin Hedström (et al.). Sleep Medicine 77, 1-6Artikel
Objective: Previous studies investigating the association between nightmares and suicide have yielded different results. We aimed to investigate whether nightmares, directly or indirectly, influence the incidence of suicide.
Methods: We used a prospective cohort study, based on 40,902 participants with a mean follow-up duration of 19.0 years. Cox proportional hazards models with attained age as time-scale were fitted to estimate hazard ratios (HR) of suicide with 95% confidence intervals (CI) as a function of the presence or absence of depression and nightmares. Mediation analysis was used to asses to what extent the relationship between nightmares and the incidence rate of suicide could be mediated by depression.
Results: No association was observed between nightmares and the incidence of suicide among participants without depression. Compared with non-depressed participants without nightmares, the incidence of suicide among participants with a diagnosis of depression was similar among those with and without nightmares (HR 12.3, 95% CI 5.55-27.2 versus HR 13.2, 95% CI 7.25-24.1). The mediation analysis revealed no significant effects of nightmares on suicide incidence. However, the incidence of depression during follow-up was higher among those who suffered from nightmares than among those who did not (p < 0.001).
Conclusions: Our findings indicate that nightmares have no influence on the incidence rate of suicide, but may reflect pre-existing depression. This is supported by a recent discovery of a strong genetic correlation of nightmares with depressive disorders, with no evidence that nightmares would predispose to psychiatric illness or psychological problems. Interventions targeting both depression and nightmares, when these conditions co-occur, may provide additional therapeutic benefit.
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.
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.
A combined fMRI and EMG study of emotional contagion following partial sleep deprivation in young and older humans
2020. Sandra Tamm (et al.). Scientific Reports 10 (1)Artikel
Sleep deprivation is proposed to inhibit top-down-control in emotion processing, but it is unclear whether sleep deprivation affects emotional mimicry and contagion. Here, we aimed to investigate effects of partial sleep deprivation on emotional contagion and mimicry in young and older humans. Participants underwent partial sleep deprivation (3 h sleep opportunity at the end of night), crossed-over with a full sleep condition in a balanced order, followed by a functional magnetic resonance imaging and electromyography (EMG) experiment with viewing of emotional and neutral faces and ratings of emotional responses. The final sample for main analyses was n = 69 (n = 36 aged 20–30 years, n = 33 aged 65–75 years). Partial sleep deprivation caused decreased activation in fusiform gyri for angry faces and decreased ratings of happiness for all stimuli, but no significant effect on the amygdala. Older participants reported more anger compared to younger participants, but no age differences were seen in brain responses to emotional faces or sensitivity to partial sleep deprivation. No effect of the sleep manipulation was seen on EMG. In conclusion, emotional contagion, but not mimicry, was affected by sleep deprivation. Our results are consistent with the previously reported increased negativity bias after insufficient sleep.
The Stockholm sleepy brain study: effects of sleep deprivation on cognitive and emotional processing in young and old. https://clinicaltrials.gov/ct2/show/NCT02000076.
Fatigue and sleepiness responses to experimental inflammation and exploratory analysis of the effect of baseline inflammation in healthy humans
2020. Julie Lasselin (et al.). Brain, behavior, and immunity 83, 309-314Artikel
Inflammation is believed to be a central mechanism in the pathophysiology of fatigue. While it is likely that dynamic of the fatigue response after an immune challenge relates to the corresponding cytokine release, this lacks evidence. Although both fatigue and sleepiness are strong signals to rest, they constitute distinct symptoms which are not necessarily associated, and sleepiness in relation to inflammation has been rarely investigated. Here, we have assessed the effect of an experimental immune challenge (administration of lipopolysaccharide, LPS) on the development of both fatigue and sleepiness, and the associations between increases in cytokine concentrations, fatigue and sleepiness, in healthy volunteers. In addition, because chronic-low grade inflammation may represent a risk factor for fatigue, we tested whether higher baseline levels of inflammation result in a more pronounced development of cytokine-induced fatigue and sleepiness. Data from four experimental studies was combined, giving a total of 120 subjects (LPS N = 79, 18 (23%) women; Placebo N = 69, 12 (17%) women). Administration of LPS resulted in a stronger increase in fatigue and sleepiness compared to the placebo condition, and the development of both fatigue and sleepiness closely paralleled the cytokine responses. Individuals with stronger increases in cytokine concentrations after LPS administration also suffered more from fatigue and sleepiness (N = 75), independent of gender. However, there was no support for the hypothesis that higher baseline inflammatory markers moderated the responses in fatigue or sleepiness after an inflammatory challenge. The results demonstrate a tight connection between the acute inflammatory response and development of both fatigue and sleepiness, and motivates further investigation of the involvement of inflammation in the pathophysiology of central fatigue.
Long-term effect of mobile phone use on sleep quality
2020. Giorgio Tettamanti (et al.). Environment International 140Artikel
Background: Effects of radiofrequency electromagnetic field exposure (RF-EMF) from mobile phone use on sleep quality has mainly been investigated in cross-sectional studies. The few previous prospective cohort studies found no or inconsistent associations, but had limited statistical power and short follow-up. In this large prospective cohort study, our aim was to estimate the effect of RF-EMF from mobile phone use on different sleep outcomes.
Materials and methods: The study included Swedish (n = 21,049) and Finnish (n = 3120) participants enrolled in the Cohort Study of Mobile Phone Use and Health (COSMOS) with information about operator-recorded mobile phone use at baseline and sleep outcomes both at baseline and at the 4-year follow-up. Sleep disturbance, sleep adequacy, daytime somnolence, sleep latency, and insomnia were assessed using the Medical Outcome Study (MOS) sleep questionnaire.
Results: Operator-recorded mobile phone use at baseline was not associated with most of the sleep outcomes. For insomnia, an odds ratio (OR) of 1.24, 95% CI 1.03-1.51 was observed in the highest decile of mobile phone call-time (> 258 min/week). With weights assigned to call-time to account for the lower RF-EMF exposure from Universal Mobile Telecommunications Service (UMTS, 3G) than from Global System for Mobile Communications (GSM, 2G) the OR was 1.09 (95% CI 0.89-1.33) in the highest call-time decile.
Conclusion: Insomnia was slightly more common among mobile phone users in the highest call-time category, but adjustment for the considerably lower RF-EMF exposure from the UMTS than the GSM network suggests that this association is likely due to other factors associated with mobile phone use than RF-EMF. No association was observed for other sleep outcomes. In conclusion, findings from this study do not support the hypothesis that RF-EMF from mobile phone use has long-term effects on sleep quality.
Night work, mortality, and the link to occupational group and sex
2020. Torbjorn Åkerstedt, Jurgita Narusyte, Pia Svedberg. Scandinavian Journal of Work, Environment and Health 46 (5), 508-515Artikel
Objective Night shifts are associated with several major diseases. Mortality has been studied only to a limited extent, and the association with night shifts remains unclear. The purpose of the present study was to investigate the association between duration of night shift exposure and mortality in a large sample from the Swedish Twin Registry (the SALT cohort).
Methods Cox proportional hazards regression models were used to analyze the data (N=42 731) over a followup period of 18 years, with years of night shift work as the exposure variable and adjustment for lifestyle factors and age, and stratification on gender and occupational group.
Results The hazard ratio (HR) for “ever” night shifts for total mortality was 1.07 [95% confidence interval (CI) 1.01–1.15] but 1.15 (95% CI 1.07–1.25) for longer exposure (>5 years). Also, HR for cause-specific mortality due to cardiovascular disease was significant, with higher HR for longer night shift exposure. Mortality due to cancer was significant for longer exposure only. White-collar workers showed significant HR for longer exposure. In particular, male white-collar workers showed a significant HR, with a highest value for longer exposure [HR 1.28 (95% CI 1.09–1.49)]. Heredity did not influence the results significantly.
Conclusions Long duration of exposure to night shift work is associated with increased mortality, particularly in male white-collar workers. The lack of effects of accumulated exposure suggests that the results should be interpreted with caution.
Prospective study of job stress and risk of infections in Swedish adults
2020. Francesca Ghilotti (et al.). Occupational and Environmental Medicine 77 (10), 681-690Artikel
Objectives Psychological stress may influence both susceptibility and severity of infections. Although work-related stress is a widespread concern among many employees, few studies have been conducted with the focus on work stressors and infections. We therefore aimed to investigate this association in a prospective cohort study.
Methods Our study included 25 029 employed individuals who filled-out a questionnaire in September 1997 and were followed through record linkages until retirement or December 2016. Work stress was assessed at baseline using a Swedish version of the Demand-Control Questionnaire, whereas hospital contacts related to infections were identified from the National Patient Register. We fitted extensions of the standard Cox model to account for recurrent infections.
Results In total, we observed 8257 infections. Individuals in the third tertile of job demand had a 13% higher hazard of infections (HR=1.13; 95% CI=1.03 to 1.24) compared with individuals in the first tertile, specifically an increased incidence of upper respiratory tract infections (HR=1.15; 95% CI=1.00 to 1.33) and urinary tract infections (HR=1.31; 95% CI=1.09 to 1.57) was found. Employees with the highest job control (third tertile) had no lower risk of infections than individuals in the lowest tertile (HR=1.02; 95% CI=0.92 to 1.13). When combining the demand and control dimensions into job strain scale, no association between high job strain and infections was observed (HR=1.08; 95% CI=0.97 to 1.21).
Conclusion High job demand, but not low job control, is associated with an increased occurrence of infections. No difference was observed in workers with high strain jobs compared with those with low strain jobs.
Sleepiness, sleep duration, and human social activity
2020. Benjamin C. Holding (et al.). Proceedings of the National Academy of Sciences of the United States of America 117 (35), 21209-21217Artikel
Daytime sleepiness impairs cognitive ability, but recent evidence suggests it is also an important driver of human motivation and behavior. We aimed to investigate the relationship between sleepiness and a behavior strongly associated with better health: social activity. We additionally aimed to investigate whether a key driver of sleepiness, sleep duration, had a similar relationship with social activity. For these questions, we considered bidirectionality, time of day, and differences between workdays and days off. Over 3 wk, 641 working adults logged their behavior every 30 min, completed a sleepiness scale every 3 h, and filled a sleep diary every morning (rendering >292,000 activity and >70,000 sleepiness datapoints). Using generalized additive mixed-effect models, we analyzed potential nonlinear relationships between sleepiness/sleep duration and social activity. Greater sleepiness predicted a substantial decrease in the probability of social activity (odds ratio 95% CI = 0.34 to 0.35 for days off), as well as a decreased duration of such activity when it did occur. These associations appear especially robust on days off and in the evenings. Social duration moderated the typical time-of-day pattern of sleepiness, with, for example, extended evening socializing associated with lower sleepiness. Sleep duration did not robustly predict next-day social activity. However, extensive social activity (>5 h) predicted up to 30 min shorter subsequent sleep duration. These results indicate that sleepiness is a strong predictor of voluntary decreases in social contact. It is possible that bouts of sleepiness lead to social withdrawal and loneliness, both risk factors for mental and physical ill health.
Teacher Stress and Students’ School Well-being
2020. Joacim Ramberg (et al.). Scandinavian Journal of Educational Research 64 (6), 816-830Artikel
Stress and stress-related complaints such as fatigue and depressed mood are common among teachers. Yet, knowledge about the links between the overall level of teacher stress within a school and individual student outcomes is scarce. This study investigates if the levels of teacher-reported stress, fatigue and depressed mood within a school are associated with students’ ratings of their school satisfaction and perceived teacher caring, respectively. Data derives from two separate data collections performed in upper secondary schools in 2016, the Stockholm School Survey (SSS) and the Stockholm Teacher Survey (STS), which were linked together (5367 students and 1045 teachers in 46 schools). Two-level linear regression analyses were performed. Results showed negative associations between school-level teacher stress, fatigue, and depressed mood and students’ school satisfaction and perceived teacher caring, even when controlling for student- and school-level sociodemographic characteristics. The ﬁndings suggest that teacher stress may have negative implications for students.
The impact of driver sleepiness on fixation-related brain potentials
2020. Christer Ahlström (et al.). Journal of Sleep Research 29 (5)Artikel
The effects of driver sleepiness are often quantified as deteriorated driving performance, increased blink durations and high levels of subjective sleepiness. Driver sleepiness has also been associated with increasing levels of electroencephalogram (EEG) power, especially in the alpha range. The present exploratory study investigated a new measure of driver sleepiness, the EEG fixation-related lambda response. Thirty young male drivers (23.6 +/- 1.7 years old) participated in a driving simulator experiment in which they drove on rural and suburban roads in simulated daylight versus darkness during both the daytime (full sleep) and night-time (sleep deprived). The results show lower lambda responses during night driving and with longer time on task, indicating that sleep deprivation and time on task cause a general decrement in cortical responsiveness to incoming visual stimuli. Levels of subjective sleepiness and line crossings were higher under the same conditions. Furthermore, results of a linear mixed-effects model showed that low lambda responses are associated with high subjective sleepiness and more line crossings. We suggest that the fixation-related lambda response can be used to investigate driving impairment induced by sleep deprivation while driving and that, after further refinement, it may be useful as an objective measure of driver sleepiness.