Autoimmune diseases in primary sclerosing cholangitis and their first-degree relatives

BACKGROUND

Primary sclerosing cholangitis (PSC) is linked to inflammatory bowel disease (IBD). However, there is limited overlap between IBD and PSC risk genes, but a stronger association between PSC and other autoimmune conditions. We aimed to assess coexistence and familial association of autoimmune disorders in PSC, and the influence of autoimmune co-morbidity on severe outcomes.

METHOD

In a matched cohort study, 1,378 individuals with PSC and 13,549 general population comparators and their first-degree relatives were evaluated. National registries provided data on diagnoses and outcomes (liver transplantation, hepatobiliary cancer, liver related death). Odds ratio (OR) of autoimmune disease was estimated by logistic regression. Fine & Gray competing risk regression estimated hazard ratios (HRs) for severe outcomes.

RESULTS

Prevalence of non-IBD, non-autoimmune hepatitis (AIH), autoimmune disease was 18% in PSC and 11% in comparators, OR 1.77(95%CI; 1.53-2.05). Highest odds were seen for celiac disease [OR 4.36(95%CI; 2.44-7.49)], sarcoidosis [OR 2.74(95%CI; 1.29-5.33)], diabetes type 1 [OR 2.91(95%CI; 2.05-4.05)], and autoimmune skin disease [OR 2.15(95%CI; 1.52-2.96)]. First-degree relatives of individuals with PSC had higher odds for developing IBD, AIH and any autoimmune disease than relatives of the comparators [OR 3.25 95% CI (2.68-3.91); OR 5.94 95% CI (2.82-12.02); OR 1.34 (95% CI: 1.19-1.50)]. Autoimmune co-morbidity in PSC was not associated with poorer outcome, HR 0.96 (95%CI; 0.71-1.28).

CONCLUSION

Individuals with PSC and their first-degree relatives had higher odds for autoimmune disease compared to matched comparators. This finding provides validation for prior genetic discoveries at a phenotypic level. Autoimmune comorbidity did not impact severe outcome.

The cascade of care for patients with chronic hepatitis delta in Southern Stockholm, Sweden for the past 30 years

BACKGROUND AND AIMS

Previous studies have shown suboptimal screening for hepatitis D virus (HDV) among patients with chronic hepatitis B (CHB). This study presents the cascade of care for HDV infection in a major secondary referral centre in Southern Stockholm, Sweden.

METHODS

HBsAg+ve patients attending Karolinska University Hospital (KUH) from 1992 to 2022 were identified. The prevalence of anti-HDV and/or HDV RNA positivity, interferon (IFN) therapy and maintained virological responses (MVR) after HDV treatment were assessed. Also, time to anti-HDV testing was analysed in relation to liver-related outcomes with logistic regression.

RESULTS

Among 4095 HBsAg+ve persons, 3703 (90.4%) underwent an anti-HDV screening; within a median of 1.8 months (range 0.0-57.1) after CHB diagnosis. This screening rate increased over time, to 97.9% in the last decade. Overall, 310 (8.4%) were anti-HDV+ve, of which 202 (65.2%) were HDV RNA+ve. Eighty-five (42%) received IFN, and 9 (10.6%) achieved MVR at the last follow-up. The predictive factors for anti-HDV screening were Asian origin, diagnosis after the year 2012, HIV co-infection (negative factor) and HBV DNA level < 2000 IU/mL in univariable analysis, while HIV co-infection was the only remaining factor in multivariable analysis. Delayed anti-HDV test >5 years was independently associated with worsened liver-related outcomes (adjusted odds ratio = 7.6, 95% CI 1.8-31.6).

CONCLUSION

Higher frequency of HDV screening than previously published data could be seen among CHB patients at KUH in a low-endemic setting. Receiving a delayed screening test seems to be associated with worse outcomes, stressing the need of a strategy for timely HDV diagnosis.

Age-specific and sex-specific risks for HCC in African-born persons with chronic hepatitis B without cirrhosis

BACKGROUND

The international recommendations of HCC surveillance for African-born persons with chronic hepatitis B (CHB) without cirrhosis are divergent, probably due to scarce data on incidence rate (IR) for HCC.

METHODS

We assembled a cohort with prospectively collected data of Swedish residents of African origin with diagnosed CHB without cirrhosis at baseline from 1990 to 2015. Data from nationwide registers were used to calculate the sex-specific IR and IR ratio (incidence rate ratios) in relation to age, comorbidities, and birth region, using a generalized linear model with a log-link function and Poisson distribution.

RESULTS

Among 3865 African-born persons with CHB without cirrhosis at baseline, 31 (0.8%; 77.4% men) developed HCC during a median of 11.1 years of follow-up, with poor survival after HCC diagnosis. The mean age at HCC diagnosis was 46.8 (SD±14.7; range 23-79) in men. HCC IR exceeded the recommended surveillance threshold of 0.2%/year at ages 54 and 59 years in men and women, respectively, and at ages 20-40 years if HCV or HDV co-infection was present. African-born men with CHB had an incidence rate ratios of 10.6 (95% CI 4.4-31.5) for HCC compared to matched African-born peers without CHB, and an incidence rate ratios of 35.3 (95% CI 16.0-88.7) compared to a matched general population.

CONCLUSIONS

African-born men with CHB without cirrhosis reached an IR of 0.2%/year between 50 and 60 years, and at younger ages if HCV or HDV co-infection was present. Our findings need further confirmation, and new cost-effectiveness analyses specific for young populations are needed, to provide personalized and cost-effective HCC surveillance.

Unmasking artifactual links: A reanalysis reveals No direct causal relationship between self-esteem and quality of social relations

A meta-analysis conducted by Harris and Orth (2020) found positive prospective cross-lagged effects between quality of social relations and self-esteem in included longitudinal studies. Harris and Orth concluded that the link between self-esteem and quality of social relations is reciprocal and characterized by a positive feedback loop. However, meta-analytic effects were estimated while controlling for a prior measurement of the outcome and such effects are known to be susceptible to artifactual (i.e. spurious) effects due to correlations with measurement errors and reversion to mediocrity. We reanalyzed the same data and found paradoxical effects indicating, simultaneously, both increasing and decreasing effects between self-esteem and social relations. These findings suggest that prospective effects between self-esteem and quality of social relations are artifactual rather than due to a true reciprocal effect. Thus, these findings have important theoretical implications and challenge both the risk regulation model, which posits that self-esteem has a causal effect on quality of social relations, and the sociometer theory, which claims that quality of relations is the cause and self-esteem the effect. The present results prompt further investigation into the underlying mechanisms driving these artifactual associations. Additionally, the study highlights the importance of considering methodological limitations in future meta-analyses to improve the accuracy of causal inferences.

Dangers of including outcome at baseline as a covariate in latent change score models: Results from simulations and empirical re-analyses

Latent change score modeling is a type of structural equation modeling used for estimating change over time. Often change is regressed on the initial value of the outcome variable. However, similarly to other regression analyses, this procedure may be susceptible to regression to the mean. The present study employed simulations as well as re-analyses of previously published data, claimed to indicate reciprocal promoting effects of vocabulary and matrix reasoning on each other's longitudinal development. Both in simulations and empirical re-analyses, when adjusting for initial value on the outcome, latent change score modeling tended to indicate an effect of a predictor on the change in an outcome even when no change had taken place. Furthermore, analyses tended to indicate a paradoxical effect on change both forward and backward in time. We conclude that results from latent change score modeling are susceptible to regression to the mean when adjusting for the initial value on the outcome. Researchers are recommended not to regress change on the initial value included in the calculation of the change score when employing latent change score modeling but, instead, to define this parameter as a covariance.

Questioning the vulnerability model: Prospective associations between low self-esteem and subsequent depression ratings may be spurious

BACKGROUND

According to the vulnerability model, low self-esteem makes people more depressed. Support for the vulnerability model comes almost exclusively from analyses using cross-lagged panel models, showing a negative effect of initial self-esteem on subsequent depression ratings when adjusting for initial depression. However, it is well known that such adjusted effects are susceptible to regression toward the mean.

METHODS

Data from four waves of measurements in five different samples (total N = 2703) were analyzed with two different cross-lagged panel models, two different random intercept cross-lagged panel models, and two different latent change score models, predicting change forwards as well as backwards in time.

RESULTS

High initial self-esteem predicted both decreased and increased depression ratings between measurements and an increase in self-esteem between measurements predicted a concurrent decrease in depression ratings.

LIMITATIONS

Only data from two western countries, Switzerland and USA, were analyzed. Whether the main finding, that a prospective effect of self-esteem on subsequent depression ratings might be spurious, applies to other countries and cultures remains an open question.

CONCLUSIONS

Due to the incongruent results, any causal effect of self-esteem on depression ratings, and thus the vulnerability model as such, cannot be corroborated by the data and models analyzed here. Instead, we propose, tentatively, that prospective associations between self-esteem and depression ratings may be spurious due to a combination of reasons, including regression toward the mean. The indication that depression might not be affected by measures to improve individuals' self-esteem is of clinical relevance.

Regression to the mean in latent change score models: an example involving breastfeeding and intelligence

Background

Latent change score models are often used to study change over time in observational data. However, latent change score models may be susceptible to regression to the mean. Earlier observational studies have identified a positive association between breastfeeding and child intelligence, even when adjusting for maternal intelligence.

Method

In the present study, we investigate regression to the mean in the case of breastfeeding and intelligence of children. We used latent change score modeling to analyze intergenerational change in intelligence, both from mothers to children and backward from children to mothers, in the 1979 National Longitudinal Survey of Youth (NLSY79) dataset (N = 6283).

Results

When analyzing change from mothers to children, breastfeeding was found to have a positive association with intergenerational change in intelligence, whereas when analyzing backward change from children to mothers, a negative association was found.

Conclusions

These discrepant findings highlight a hidden flexibility in the analytical space and call into question the reliability of earlier studies of breastfeeding and intelligence using observational data.

Sleepy drivers on a slippery road: A pilot study using a driving simulator

Sleepy drivers have problems with keeping the vehicle within the lines, and might often need to apply a sudden or hard corrective steering wheel movement. Such movements, if they occur while driving on a slippery road, might increase the risk of ending off road due to the unforgiving nature of slippery roads. We tested this hypothesis. Twelve young men participated in a driving simulator experiment with two counterbalanced conditions; dry versus slippery road × day (alert) versus night (sleepy) driving. The participants drove 52.5 km on a monotonous two-lane highway and rated their sleepiness seven times using the Karolinska Sleepiness Scale. Blink durations were extracted from an electrooculogram. The standard deviation of lateral position and the smoothness of steering events were measures of driving performance. Each outcome variable was analysed with mixed-effect models with road condition, time-of-day and time-on-task as predictors. The Karolinska Sleepiness Scale increased with time-on-task (p < 0.001) and was higher during night drives (p < 0.001), with a three-way interaction suggesting a small increased sleepiness with driving time at night with slippery road conditions (p = 0.012). Blink durations increased with time-on-task (p < 0.01) with an interaction between time-of-day and road condition (p = 0.040) such that physiological sleepiness was lower for sleep-deprived participants in demanding road conditions. The standard deviation of lateral position increased with time-on-task (p = 0.026); however, during night driving it was lower on a slippery road (p = 0.025). The results indicate that driving in demanding road condition (i.e. slippery road) might further exhaust already sleepy drivers, although this is not clearly reflected in driving performance.

Sleepiness as motivation: a potential mechanism for how sleep deprivation affects behavior

STUDY OBJECTIVES

To determine how sleepiness and sleep deprivation drive the motivation to engage in different behaviors.

METHODS

We studied the sleepiness of 123 participants who had been randomized to sleep deprivation or normal sleep, and their willingness to engage in a range of everyday behaviors.

RESULTS

Self-reported sleepiness was a strong predictor of the motivation to engage in sleep-preparatory behaviors such as shutting one's eyes (OR = 2.78, 95% CI: 2.19-3.52 for each step up on the Karolinska Sleepiness Scale) and resting (OR = 3.20, CI: 2.46-4.16). Sleepiness was also related to the desire to be cared for by a loved one (OR = 1.49, CI: 1.22-1.82), and preparedness to utilize monetary and energy resources to get to sleep. Conversely, increased sleepiness was associated with a decreased motivation for social and physical activities (e.g. be with friends OR = 0.71, CI: 0.61-0.82; exercise OR = 0.65, CI: 0.56-0.76). Sleep deprivation had similar effects as sleepiness on these behaviors. Neither sleepiness nor sleep deprivation had strong associations with hunger, thirst, or food preferences.

CONCLUSIONS

Our findings indicate that sleepiness is a dynamic motivational drive that promotes sleep-preparatory behaviors and competes with other drives and desired outcomes. Consequently, sleepiness may be a central mechanism by which impaired alertness, for example, due to insufficient sleep, contributes to poor quality of life and adverse health. We propose that sleepiness helps organize behaviors toward the specific goal of assuring sufficient sleep, in competition with other needs and incentives. A theoretical framework on sleepiness and its behavioral consequences are likely to improve our understanding of several disease mechanisms.

Quantifying Cognitive Impairment After Sleep Deprivation at Different Times of Day: A Proof of Concept Using Ultra-Short Smartphone-Based Tests

Cognitive functioning is known to be impaired following sleep deprivation and to fluctuate depending on the time of day. However, most methods of assessing cognitive performance remain impractical for environments outside of the lab. This study investigated whether 2-min smartphone-based versions of commonly used cognitive tests could be used to assess the effects of sleep deprivation and time of day on diverse cognitive functions. After three nights of normal sleep, participants (N = 182) were randomised to either one night of sleep deprivation or a fourth night of normal sleep. Using the Karolinska WakeApp (KWA), participants completed a battery of 2-min cognitive tests, including measures of attention, arithmetic ability, episodic memory, working memory, and a Stroop test for cognitive conflict and behavioural adjustment. A baseline measurement was completed at 22:30 h, followed by three measurements the following day at approximately 08:00 h, 12:30 h, and 16:30 h. Sleep deprivation led to performance impairments in attention, arithmetic ability, episodic memory, and working memory. No effect of sleep deprivation was observed in the Stroop test. There were variations in attention and arithmetic test performance across different times of day. The effect of sleep deprivation on all cognitive tests was also found to vary at different times of day. In conclusion, this study shows that the KWA's 2-min cognitive tests can be used to detect cognitive impairments following sleep deprivation, and fluctuations in cognitive performance relating to time of day. The results demonstrate the potential of using brief smartphone-based tasks to measure a variety of cognitive abilities within sleep and fatigue research.

The new accounting for expected adjusted effect test (AEAE test) has higher positive predictive value than a zero-order significance test

OBJECTIVE

The present simulation study aimed to assess positive predictive value (PPV) and negative predictive value (NPV) for our newly introduced Accounting for Expected Adjusted Effect test (AEAE test) and compare it to PPV and NPV for a traditional zero-order significance test.

RESULTS

The AEAE test exhibited greater PPV compared to a traditional zero-order significance test, especially with a strong true adjusted effect, low prior probability, high degree of confounding, large sample size, high reliability in the measurement of predictor X and outcome Y, and low reliability in the measurement of confounder Z. The zero-order significance test, on the other hand, exhibited higher NPV, except for some combinations of high degree of confounding and large sample size, or low reliability in the measurement of Z and high reliability in the measurement of X/Y, in which case the zero-order significance test can be completely uninformative. Taken together, the findings demonstrate desirable statistical properties for the AEAE test compared to a traditional zero-order significance test.

A comparison of models with weight, height, and BMI as predictors of mortality

Introduction

Body mass index (BMI) is a composite variable of weight and height, often used as a predictor of health outcomes, including mortality. The main purpose of combining weight and height in one variable is to obtain a measure of obesity independent of height. It is however unclear how accurate BMI is as a predictor of mortality compared with models including both weight and height or a weight × height interaction as predictors.

Methods

The current study used conscription data on weight, height, and BMI of Swedish men (N = 48,904) in 1969/70 as well as linked data on mortality (3442 deaths) between 1969 and 2008. Cox proportional hazard models including combinations of weight, height, and BMI at conscription as predictors of subsequent all-cause and cause-specific mortality were fitted to data.

Results

An increase by one standard deviation on weight and BMI were associated with an increase in hazard for all-cause mortality by 5.4% and 11.5%, respectively, while an increase by one standard deviation on height was associated with a decrease in hazard for all-cause mortality by 9.4%. The best-fitting model indicated lowest predicted all-cause mortality for those who weighed 60.5 kg at conscription, regardless of height. Further analyses of cause-specific mortality suggest that this weight seems to be a compromise between lower optimal weights to avoid cancer and CVD mortality and a higher optimal weight to not die by suicide.

Conclusions

According to the present findings, there are several ways to make better use of measured weight and height than to calculate BMI when predicting mortality.

Accounting for Expected Adjusted Effect

The point that adjustment for confounders do not always guarantee protection against spurious findings and type 1-errors has been made before. The present simulation study indicates that for traditional regression methods, this risk is accentuated by a large sample size, low reliability in the measurement of the confounder, and high reliability in the measurement of the predictor and the outcome. However, this risk might be attenuated by calculating the expected adjusted effect, or the required reliability in the measurement of the possible confounder, with equations presented in the present paper.

Threshold-like associations as a function of disturbance

According to the intelligence-creativity threshold hypothesis, there should be a positive association between intelligence and creative potential up to a certain point, the threshold, after which a further increase in intelligence should have no association with creativity. In the present simulation study, the measured intelligence and creativity of virtual subjects were affected by their true abilities as well as a disturbance factor that varied in magnitude between subjects. The results indicate that the hypothesized threshold-like association could be due to some disturbing factor, for example, low motivation, illness, or linguistic confusion, that varies between individuals and that affects both measured intelligence and measured creativity, especially if the actual association between intelligence and creativity is weak. This, together with previous negative findings, calls the validity of the intelligence-creativity threshold hypothesis into question.

Predicting the Effect of a Predictor When Controlling for Baseline

The present simulation study indicates that a method where the regression effect of a predictor (X) on an outcome at follow-up (Y1) is calculated while adjusting for the outcome at baseline (Y0) can give spurious findings, especially when there is a strong correlation between X and Y0 and when the test-retest correlation between Y0 and Y1 is relatively weak. Researchers wishing to avoid spurious findings and Type 1 errors should be aware of this phenomenon and are recommended to verify found effects by an unadjusted effect of X on the Y1-Y0 difference.

Sleep during naturally occurring respiratory infections: A pilot study

There is strong experimental support that infections increase the drive for sleep in animals, and it is widely believed that more sleep is part of an adaptive immune response. While respiratory infections (RI) are very prevalent in humans, there is a striking lack of systematic knowledge on how it affects sleep. We recruited 100 people, among whom 28 became sick with an RI during the study period (fulfilling criteria for influenza-like illness, ILI, or acute respiratory infection, ARI). We measured sick participants' sleep at home, both objectively (actigraphy) and subjectively (diary ratings), for one week as well as four weeks later when healthy. During the week with RI, people spent objectively longer time in bed and had a longer total sleep time compared to the healthy week. During the infection, participants also had more awakenings, but no significant differences in sleep latency or sleep efficiency. While sick, people also reported increased difficulties falling asleep, worse sleep quality, more restless sleep and more shallow sleep, while they did not report sleep to be less sufficient. Most problems occurred at the beginning of the sickness week, when symptoms were strong, and showed signs of recovery thereafter (as indicated by interactions between condition and day/night of data collection for all the 10 sleep outcomes). The degree of symptoms of RI was related to a worse sleep quality and more restless sleep, but not to any of the objective sleep outcomes or the other subjective sleep variables. Having a higher body temperature was not significantly related to any of the sleep variables. This study suggests that having a respiratory infection is associated with spending more time in bed and sleeping longer, but also with more disturbed sleep, both objectively and subjectively. This novel study should be seen as being of pilot character. There is a need for larger studies which classify pathogen type and include baseline predictors, or that manipulate sleep, in order to understand whether the sleep alterations seen during infections are adaptive and whether sleep interventions could be used to improve recovery from respiratory infections.

Estimating statistical power, posterior probability and publication bias of psychological research using the observed replication rate

In this paper, we show how Bayes' theorem can be used to better understand the implications of the 36% reproducibility rate of published psychological findings reported by the Open Science Collaboration. We demonstrate a method to assess publication bias and show that the observed reproducibility rate was not consistent with an unbiased literature. We estimate a plausible range for the prior probability of this body of research, suggesting expected statistical power in the original studies of 48-75%, producing (positive) findings that were expected to be true 41-62% of the time. Publication bias was large, assuming a literature with 90% positive findings, indicating that negative evidence was expected to have been observed 55-98 times before one negative result was published. These findings imply that even when studied associations are truly NULL, we expect the literature to be dominated by statistically significant findings.

Validating and extending the three process model of alertness in airline operations

Sleepiness and fatigue are important risk factors in the transport sector and bio-mathematical sleepiness, sleep and fatigue modeling is increasingly becoming a valuable tool for assessing safety of work schedules and rosters in Fatigue Risk Management Systems (FRMS). The present study sought to validate the inner workings of one such model, Three Process Model (TPM), on aircrews and extend the model with functions to model jetlag and to directly assess the risk of any sleepiness level in any shift schedule or roster with and without knowledge of sleep timings. We collected sleep and sleepiness data from 136 aircrews in a real life situation by means of an application running on a handheld touch screen computer device (iPhone, iPod or iPad) and used the TPM to predict sleepiness with varying level of complexity of model equations and data. The results based on multilevel linear and non-linear mixed effects models showed that the TPM predictions correlated with observed ratings of sleepiness, but explorative analyses suggest that the default model can be improved and reduced to include only two-processes (S+C), with adjusted phases of the circadian process based on a single question of circadian type. We also extended the model with a function to model jetlag acclimatization and with estimates of individual differences including reference limits accounting for 50%, 75% and 90% of the population as well as functions for predicting the probability of any level of sleepiness for ecological assessment of absolute and relative risk of sleepiness in shift systems for safety applications.

Subjective health perception in healthy young men changes in response to experimentally restricted sleep and subsequent recovery sleep

Sleep and subjective health are both prospectively related to objective indices of health and health care use. Here, we tested whether five days with restricted sleep and subsequent recovery days affect subjective health and is related to increased levels of circulating IL-6 and TNF-α and fatigue. Nine healthy men (23-28 ears) went through a 6-week sleep protocol with subjects as their own controls in a repeated measures design with a total of 11 nights in a sleep laboratory. The experimental part of the protocol included three baseline days (sleep 23-07 h), five days with sleep restriction (03-07 h) and three recovery days (23-07 h) in the sleep laboratory. Subjective health and fatigue was recorded daily. Eight blood samples were drawn each day (every third hour) on 8 days of the protocol and analyzed with respect to IL-6 and TNF-α. Subjective health deteriorated gradually during restricted sleep (p=.002) and returned to baseline levels after three days of recovery. IL-6 and TNF-α did not change significantly. Fatigue increased gradually during sleep restriction (p=.001), which significantly contributed to the association between restricted sleep and subjective health. The study is the first to show that subjective health is directly responsive to changes in sleep length and related to increased fatigue. Thus, subjective health is differently appraised after manipulation of one of its presumed determinants. Larger experimental studies would be beneficial to further distinguish causation from association regarding the underpinnings of subjective health.

Factor structure and longitudinal measurement invariance of the demand control support model: an evidence from the Swedish Longitudinal Occupational Survey of Health (SLOSH)

OBJECTIVES

To examine the factor structure and to evaluate the longitudinal measurement invariance of the demand-control-support questionnaire (DCSQ), using the Swedish Longitudinal Occupational Survey of Health (SLOSH).

METHODS

A confirmatory factor analysis (CFA) and multi-group confirmatory factor analysis (MGCFA) models within the framework of structural equation modeling (SEM) have been used to examine the factor structure and invariance across time.

RESULTS

Four factors: psychological demand, skill discretion, decision authority and social support, were confirmed by CFA at baseline, with the best fit obtained by removing the item repetitive work of skill discretion. A measurement error correlation (0.42) between work fast and work intensively for psychological demands was also detected. Acceptable composite reliability measures were obtained except for skill discretion (0.68). The invariance of the same factor structure was established, but caution in comparing mean levels of factors over time is warranted as lack of intercept invariance was evident. However, partial intercept invariance was established for work intensively.

CONCLUSION

Our findings indicate that skill discretion and decision authority represent two distinct constructs in the retained model. However removing the item repetitive work along with either work fast or work intensively would improve model fit. Care should also be taken while making comparisons in the constructs across time. Further research should investigate invariance across occupations or socio-economic classes.

Sleep, physical activity and BMI in six to ten-year-old children measured by accelerometry: a cross-sectional study

Background

The aim of this study is to describe the relationship between objective measures of sleep, physical activity and BMI in Swedish pre-adolescents. The day-to-day association between physical activity and sleep quality as well as week-day and weekend pattern of sleep is also described.

Method

We conducted a cross sectional study consisted of a cohort of 1.231 children aged six to ten years within the Stockholm county area. Sleep and physical activity were measured by accelerometry during seven consecutive days. Outcome measures are total sleep time, sleep efficiency, sleep start and sleep end; physical activity intensity divided into: sedentary (<1.5 METS), light (1.5 to 3 METS) and moderate-to-vigorous (> 3 METS); and Body Mass Index standard deviations score, BMIsds.

Results

Total sleep time decreased with increasing age, and was shorter in boys than girls on both weekdays and weekends. Late bedtime but consistent wake-up time during weekends made total sleep time shorter on weekends than on weekdays. Day-to-day within-subject analysis revealed that moderate-to-vigorous intense physical activity promoted an increased sleep efficiency the following night (CI < 0.001 to 0.047), while total sleep time was not affected (CI -0.003 to 0.043). Neither sleep duration (CI -0.024 to 0.022) nor sleep efficiency (CI -0.019 to 0.028) affected mean physical activity level the subsequent day. The between-subject analysis indicates that the sleep of children characterized by high moderate-to-vigorous physical activity during the day was frequently interrupted (SE = -.23, P < .01). A negative association between BMIsds and sleep duration was found (-.10, p < .01).

Conclusions

Short sleep duration was associated with high BMI in six to ten year old children. This study underscores the importance of consistent bedtimes throughout the week for promoting sleep duration in preadolescents. Furthermore, this study suggests that a large proportion of intensive physical activity during the day might promote good sleep quality.

Beauty sleep: experimental study on the perceived health and attractiveness of sleep deprived people

OBJECTIVE

To investigate whether sleep deprived people are perceived as less healthy, less attractive, and more tired than after a normal night's sleep.

DESIGN

Experimental study.

SETTING

Sleep laboratory in Stockholm, Sweden.

PARTICIPANTS

23 healthy, sleep deprived adults (age 18-31) who were photographed and 65 untrained observers (age 18-61) who rated the photographs.

INTERVENTION

Participants were photographed after a normal night's sleep (eight hours) and after sleep deprivation (31 hours of wakefulness after a night of reduced sleep). The photographs were presented in a randomised order and rated by untrained observers.

MAIN OUTCOME MEASURE

Difference in observer ratings of perceived health, attractiveness, and tiredness between sleep deprived and well rested participants using a visual analogue scale (100 mm).

RESULTS

Sleep deprived people were rated as less healthy (visual analogue scale scores, mean 63 (SE 2) v 68 (SE 2), P<0.001), more tired (53 (SE 3) v 44 (SE 3), P<0.001), and less attractive (38 (SE 2) v 40 (SE 2), P<0.001) than after a normal night's sleep. The decrease in rated health was associated with ratings of increased tiredness and decreased attractiveness.

CONCLUSION

Our findings show that sleep deprived people appear less healthy, less attractive, and more tired compared with when they are well rested. This suggests that humans are sensitive to sleep related facial cues, with potential implications for social and clinical judgments and behaviour. Studies are warranted for understanding how these effects may affect clinical decision making and can add knowledge with direct implications in a medical context.

The importance of individual preferences when evaluating the associations between working hours and indicators of health and well-being

Previous studies indicate that the effect of a given shift schedule may depend on individual factors. The aim of the present study was to investigate whether a misfit between individual preferences and actual working hours affected the association between working hours and self-reported indicators of health and well-being. The study population consisted of 173 female eldercare workers who mainly worked day or evening shifts. We combined self-reported questionnaire data on preferences with actual work schedules during a four-week period. The study showed that a misfit between preferences on one hand and "non-day work", "weekend work" or "only a few consecutive days off" on the other hand was associated with an increased dissatisfaction with working hours and/or an increase in the intention to leave the workplace due to one's working hours.

Reaction of sleepiness indicators to partial sleep deprivation, time of day and time on task in a driving simulator--the DROWSI project

Studies of driving and sleepiness indicators have mainly focused on prior sleep reduction. The present study sought to identify sleepiness indicators responsive to several potential regulators of sleepiness: sleep loss, time of day (TOD) and time on task (TOT) during simulator driving. Thirteen subjects drove a high-fidelity moving base simulator in six 1-h sessions across a 24-h period, after normal sleep duration (8 h) and after partial sleep deprivation (PSD; 4 h). The results showed clear main effects of TOD (night) and TOT but not for PSD, although the latter strongly interacted with TOD. The most sensitive variable was subjective sleepiness, the standard deviation of lateral position (SDLAT) and measures of eye closure [duration, speed (slow), amplitude (low)]. Measures of electroencephalography and line crossings (LCs) showed only modest responses. For most variables individual differences vastly exceeded those of the fixed effects, except for subjective sleepiness and SDLAT. In a multiple regression analysis, SDLAT, amplitude/peak eye-lid closing velocity and blink duration predicted subjective sleepiness bouts with a sensitivity and specificity of about 70%, but were mutually redundant. The prediction of LCs gave considerably weaker, but similar results. In summary, SDLAT and eye closure variables could be candidates for use in sleepiness-monitoring devices. However, individual differences are considerable and there is need for research on how to identify and predict individual differences in susceptibility to sleepiness.

Variation in Sleepiness during Early Morning Shifts: A Mixed Model Approach to an Experimental Field Study of Train Drivers

The present study aimed to experimentally evaluate the effect of early morning shifts on sleep and sleepiness of train drivers during normal working conditions. A total of 17 experienced train drivers were studied during a 4.5 h drive in two directions with a 2.5 h break in between on three different shifts: an early shift that started at 05:49 h (train left at 06:18 h) and ended at 17:41h, a day shift (07:49-19:41 h), and an evening shift (09:49-21:41 h). Retrospective (since the last stop) ratings of mean sleepiness and peak sleepiness (Karolinska Sleepiness Scale--KSS: 1 = very alert, 9= very sleepy, fighting sleep, difficulty staying awake) were assessed at each stop during the drive. The results showed that sleep length was reduced (p <0.001) by 1 h and 2h, respectively, by the early shift compared to the day and evening shifts. The prevalence of severe sleepiness (KSS > or = 7) was high, especially during the early shift when 14 (82%) subjects reported at least one event during the drive. Application of the Generalized Linear Mixed Models (GLMM) to the sleepiness data showed that there was an increased risk for severe sleepiness during the early shift (OR = 4.9) that increased further with the length of the drive between stops (OR = 1.9, 15 min), suggesting an interaction between early morning shift and monotony. The findings have practical implications in risk assessment. Long drives without stops and other monotonous situations should have a higher risk rating for severe sleepiness in shifts with an early start before 06:00 h, compared to shifts that begin 2 h later.

Sleep homeostasis during repeated sleep restriction and recovery: support from EEG dynamics

STUDY OBJECTIVES

Sleep reduction normally causes a homeostatic response during subsequent recovery sleep, but this does not seem to be true for repeated partial sleep loss. The aim of the present study was to test the response to repeated partial sleep loss through detailed focus on spectral data and parts of sleep.

DESIGN

The experiment involved 4 h of sleep across 5 days in the laboratory (partial sleep deprivation [PSD]), followed by 3 days of recovery sleep. PSD was achieved through a delayed bedtime. Nine individuals participated. To avoid "laboratory monotony," subjects were permitted to leave the lab for a few hours each day.

MEASUREMENTS AND RESULTS

All sleep stages and the latencies to sleep and slow wave sleep (SWS) showed a significant reduction during PSD. However, SWS and TST (total sleep time) during the first half of sleep increased gradually across days with PSD. During the first recovery sleep, SWS was significantly increased, while stage 1 and latency to stage 3 were reduced. All were back to baseline on the second night of recovery sleep. Summed spectral power during the first 3.8 h of sleep showed a gradual and robust increase (50% above baseline) in the range 1.25-7.25 Hz across days with PSD up to first recovery sleep and then returned to baseline.

CONCLUSIONS

SWS and summed power density in a broad low-frequency band respond to repeated partial sleep deprivation in a dose-response fashion during the first 4 h sleep, apparently reflecting a robust and stable homeostatic response to sleep loss.

Sleepiness and performance in response to repeated sleep restriction and subsequent recovery during semi-laboratory conditions

There is an ongoing debate of how best to measure the effects of sleep loss in a reliable and feasible way, partly because well controlled laboratory studies and field studies have come to different conclusions. The aims of the present study were to investigate both sleepiness and performance in response to long-term sleep restriction and recovery in a semi-laboratory environment, investigate order effects (i.e., whether levels return to baseline) in a study with seven days of recovery, and characterize individual differences in tolerance to restricted sleep. Nine healthy men (age 23-28 yrs) participated in the protocol, which included one habituation day (sleep 23:00-07:00 h), two baseline days (23:00-07:00 h), five days with restricted sleep (03:00-07:00 h), and seven recovery days (23:00-07:00 h). Participants went outdoors at least twice each day. Reaction-time tests were performed at 08:00, 14:00, and 20:00 h each day in the laboratory. Sleepiness was self-rated by the Karolinska Sleepiness Scale (KSS)after each test. The mixed-effect regression models showed that each day of restricted sleep resulted in an increase of sleepiness by 0.64+/- .05 KSS units (a nine-step scale, p < .001), increase of median reaction times of 6.6+/- 1.6 ms ( p = .003), and increase of lapses/test of 0.69 +/- .16 ms ( p < .001). Seven days of recovery allowed participants to return to the baseline for sleepiness and median reaction time, but not for lapses. The individual differences were larger for performance measures than for sleepiness; the between-subject standard deviation for the random intercept was in the magnitude of the effects of 1.1 days of restricted sleep for sleepiness, 6.6 days of restricted sleep for median reaction time, and 3.2 days for lapses. In conclusion, the present study shows that sleepiness is closely related to sleep pressure, while performance measures, to a larger extent, appear determined by specific individual traits. Moreover, it is suggested to measure sleepiness in a standardized situation so as to minimize the influences of contextual factors.

Subjective sleepiness and accident risk avoiding the ecological fallacy

The present study of sleepiness and accident risk in a HI-FI car simulator aimed to provide subject-level relative risks (RR) with 95% confidence intervals (CI) for different levels of subjective sleepiness measured with the Karolinska Sleepiness Scale (KSS), 1 = very alert, 9 = very sleepy, fighting sleep, an effort to staying awake. Five male and five female shift workers, mean age 37 years, participated with a 2-h drive (08:00-10:00 hours) in a dynamic high-fidelity moving base driving simulator, after a night of work and after a night of sleep. Subjective sleepiness was measured with KSS every 5 min and events of incidents (two wheels outside the right lane), accidents (two wheels off the road or four wheels in opposite lane) and crashes (four wheels off the road) were recorded. The probability of an accident was modelled with a Generalized Linear Mixed Model approach to estimate subject-specific effects, rather than group average effects, to avoid the ecological fallacy. The results showed that sleepiness was strongly related to accident risk. An average subject was estimated at 28.2 times (95% CI RR = 10.7-74.1) increased risk at KSS = 8 and at 185 times (95% CI RR = 42-316) at KSS = 9 compared with KSS = 5. There were large individual differences in event propensity that complicates the prediction of absolute accident risk for individual subjects.

Subjective sleepiness, simulated driving performance and blink duration: examining individual differences

The present study aimed to provide subject-specific estimates of the relation between subjective sleepiness measured with the Karolinska Sleepiness Scale (KSS) and blink duration (BLINKD) and lane drifting calculated as the standard deviation of the lateral position (SDLAT) in a high-fidelity moving base driving simulator. Five male and five female shift workers were recruited to participate in a 2-h drive (08:00-10:00 hours) after a normal night sleep and after working a night shift. Subjective sleepiness was rated on the KSS in 5-min intervals during the drive, electro-occulogram (EOG) was measured continuously to calculate BLINKD, and SDLAT was collected from the simulator. A mixed model anova showed a significant (P < 0.001) effect of the KSS for both dependent variables. A test for a quadratic trend suggests a curvilinear effect with a steeper increase at high KSS levels for both SDLAT (P < 0.001) and BLINKD (P = 0.003). Large individual differences were observed for the intercept (P < 0.001), suggesting that subjects differed in their overall driving performance and blink duration independent of sleepiness levels. The results have implications for any application that needs prediction at the subject level (e.g. driver fatigue warning systems) as well as for research design and the interpretation of group average data.

Effects of acutely displaced sleep on testosterone

CONTEXT

It is not yet clear whether the diurnal variation in testosterone is regulated by circadian or homeostatic (sleep) influences.

OBJECTIVE

The present study tested whether testosterone is driven by a circadian-independent sleep effect by shifting sleep acutely to daytime in a 24-h sampling regiment.

DESIGN, SETTING, AND PARTICIPANTS

In the sleep laboratory, seven healthy young men (age, 22-32 yr) participated in three conditions: habituation (sleep between 2300-0700 h), night sleep (2300-0700 h), and day sleep (0700-1500 h), the latter two in a balanced order.

INTERVENTION AND MAIN OUTCOME MEASURE

Serum testosterone was, in all conditions, sampled by hourly blood drawing for 24 h during constant bed rest.

RESULTS

Mean testosterone levels increased as a log-linear function of time (hours) across both sleep periods (b = 4.88; P < 0.001), from 15.3 +/- 2.1 to 25.3 +/- 2.2 nmol/liter during night sleep and from 17.3 +/- 2.1 to 26.4 +/- 2.9 nmol/liter during day sleep. Similarly, mean testosterone levels decreased with time (log-linear) awake (b = -1.80; P < 0.001). There was also evidence of a weak circadian component (acrophase ranging between 0651-0924 h) and an increase with time in the laboratory. Moreover, all these effects, except for the increase during sleep, differed significantly between individuals.

CONCLUSION

In conclusion, testosterone increased during sleep and fell during waking, whereas circadian effects seemed marginal. Individual differences were pronounced.

Effect of accumulated night work during the working lifetime, on subjective health and sleep in monozygotic twins

The present study sought to investigate the effects of lifetime accumulated night work on subjective health and sleep in monozygotic twins discordant on the exposure to night work. A total of 169 twin pairs (83 males, 86 females) over 65 years of age were analyzed on variables that describe the presence or absence of complaints regarding subjective health, disturbed sleep, repeated awakenings and not being well rested. Significant (P < 0.05) risk ratios (RR) were found for subjective health (RR = 1.67) and disturbed sleep (RR = 2.83) indicating a higher risk of developing complaints to former night workers. There was neither a dose-dependent effect of night work nor an interaction effect with gender observed.

A shorter workday as a means of reducing the occurrence of musculoskeletal disorders

OBJECTIVES

The study examined the relation between daily workhours and the occurrence of neck-shoulder or back pain in physically demanding care work.

METHODS

Unpublished data were obtained from three intervention projects in care institutions. The projects had been conducted independently in Oslo (46 participants, 175 referents before and 158 referents after the intervention), Helsingborg (60 participants, 89 referents) and Stockholm (41 participants, 22 referents) between 1995 and 1998. The intervention was a reduction of daily workhours from > or = 7 to 6 hours (or 30 hours weekly). Full-time salary was retained, and extra personnel were employed to compensate for the reduction in workhours. Data were collected by self-administered questionnaires before and during the intervention periods, lasting from 12 to 22 months.

RESULTS

The prevalence of neck-shoulder pain decreased from 40.9% to 25.6% in Oslo and from 57.1% to 39.1% in Helsingborg after 1.5 years with a 6-hour workday; for Stockholm the decrease was from 81.6% to 68.3% after 1 year. No decrease was observed in the reference groups. The prevalence of back pain did not show the same consistent pattern.

CONCLUSIONS

The shortening of regular workdays from > or = 7 hours to 6 hours may considerably reduce the prevalence of neck-shoulder pain among persons with physically demanding care work. The potential health benefits should encourage intervention studies also in other occupations with increased risk of work-related musculoskeletal disorders.

A 6-hour working day--effects on health and well-being

The effect of the total amount of work hours and the benefits of a shortening is frequently debated, but very little data is available. The present study compared a group (N = 41) that obtained a 9 h reduction of the working week (to a 6 h day) with a comparison group (N = 22) that retained normal work hours. Both groups were constituted of mainly female health care and day care nursery personnel. The experimental group retained full pay and extra personnel were employed to compensate for loss of hours. Questionnaire data were obtained before and 1 year after the change. The data were analyzed using a two-factor ANOVA with the interaction term year*group as the main focus. The results showed a significant interaction of year*group for social factors, sleep quality, mental fatigue, and heart/respiratory complaints, and attitude to work hours. In all cases the experimental group improved whereas the control group did not change. It was concluded that shortened work hours have clear social effects and moderate effects on well-being.