The association of short and long sleep with mortality in men and women.

Both short (< 6 hr) and long (> 8 hr) sleep are associated with increased mortality. We here investigated whether the association between sleep duration and all-cause, cardiovascular disease and cancer mortality differs between men and women. A cohort of 34,311 participants (mean age and standard deviation = 50.5 ± 15.5 years, 65% women), with detailed assessment of sleep at baseline and up to 20.5 years of follow-up (18 years for cause-specific mortality), was analysed using Cox proportional hazards model to estimate HRs with 95% confidence intervals. After adjustment for covariates, all-cause, cardiovascular disease and cancer mortalities were increased for both < 5 hr and ≥ 9 hr sleep durations (with 6 hr as reference). For all-cause mortality, women who slept < 5 hr had a hazard ratio = 1.54 (95% confidence interval = 1.32-1.80), while the corresponding hazard ratio was 1.05 (95% confidence interval = 0.88-1.27) for men, the interaction being significant (p < 0.05). For cardiovascular disease mortality, exclusion of the first 2 years of exposure, as well as competing risk analysis eliminated the originally significant interaction. Cancer mortality did not show any significant interaction. Survival analysis of the difference between the reference duration (6 hr) and the short duration (< 5 hr) during follow-up showed a gradually steeper reduction of survival time for women than for men for all-cause mortality. We also observed that the lowest cancer mortality appeared for the 5-hr sleep duration. In conclusion, the pattern of association between short sleep duration and all-cause mortality differed between women and men, and the difference between men and women increased with follow-up time.

Insufficient sleep during adolescence and risk of multiple sclerosis: results from a Swedish case-control study.

BACKGROUND: Shift work, which often results in sleep deprivation and circadian desynchrony, has been associated with increased risk of multiple sclerosis (MS). We aimed at studying the impact of sleep duration, circadian disruption and sleep quality on MS risk. METHODS: We used a Swedish population-based case-control study (2075 cases, 3164 controls). Aspects of sleep were associated with MS risk by calculating OR with 95% CIs using logistic regression models. RESULTS: Compared with sleeping 7-9 hours/night during adolescence, short sleep (<7 hours/night) was associated with increased risk of developing MS (OR 1.4, 95% OR 1.1-1.7). Similarly, subjective low sleep quality during adolescence increased the risk of subsequently developing MS (OR 1.5, 95% CI 1.3 to 1.9), whereas phase shift did not significantly influence the risk. Our findings remained similar when those who worked shifts were excluded. CONCLUSIONS: Insufficient sleep and low sleep quality during adolescence seem to increase the risk of subsequently developing MS. Sufficient restorative sleep at young age, needed for adequate immune functioning, may be a preventive factor against MS.

A comparison of sleep restriction and sleep compression on objective measures of sleep: A sub-sample from a large randomised controlled trial.

Sleep restriction therapy is a central component of cognitive behavioural therapy for insomnia, but can lead to excessive sleepiness, which may impede treatment adherence. Sleep compression therapy has been suggested as a possibly gentler alternative. The aim of this study was to compare the effects of sleep restriction therapy and sleep compression therapy on objective measures of sleep, with a focus on magnitude and timing of effects. From a larger study of participants with insomnia, a sub-sample of 36 underwent polysomnographic recordings, before being randomised to either sleep restriction (n = 19) or sleep compression (n = 17) and receiving online treatment for 10 weeks. Assessments with polysomnography were also carried out after 2, 5, and 10 weeks of treatment. Data were analysed with multilevel linear mixed effect modelling. As per treatment instructions, participants in sleep restriction initially spent shorter time in bed compared with sleep compression. Participants in sleep restriction also showed an initial decrease of total sleep time, which was not seen in the sleep compression group. Both treatments led to improvements in sleep continuity variables, with a tendency for the improvements to come earlier during treatment in sleep restriction. No substantial differences were found between the two treatments 10 weeks after the treatment start. The results indicate that homeostatic sleep pressure may not be as important as a mechanism in sleep compression therapy as in sleep restriction therapy, and an investigation of other mechanisms is needed. In conclusion, the treatments led to similar changes in objective sleep at a somewhat different pace, and possibly through different mechanisms.

Interactive association between insomnia symptoms and sleep duration for the risk of dementia-a prospective study in the Swedish National March Cohort.

OBJECTIVE: Given the importance of sleep in maintaining neurocognitive health, both sleep duration and quality might be component causes of dementia. However, the possible role of insomnia symptoms as risk factors for dementia remain uncertain. METHODS: We prospectively studied 22,078 participants in the Swedish National March Cohort who were free from dementia and stroke at baseline. Occurrence of dementia was documented by national registers during a median follow-up period of 19.2 years. Insomnia symptoms and sleep duration were ascertained by Karolinska Sleep Questionnaire. Multivariable Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI). RESULTS: Compared to participants without insomnia at baseline, those who reported any insomnia symptom experienced a greater incidence of dementia during follow-up (HR 1.08, 95% CI: 1.03, 1.35). Difficulty initiating sleep versus non-insomnia (HR 1.24, 95% CI: 1.02, 1.52), but not difficulty maintaining sleep or early morning awakening was associated with an increased risk of dementia. Short sleep duration was associated with increased risk of dementia (6 h vs. 8 h, HR 1.29, 95% CI: 1.11-1.51; 5 h vs. 8 h, HR 1.26, 95% CI: 1.00-1.57). Stratified analyses suggested that insomnia symptoms increased the risk of dementia only amongst participants with ≥7 h sleep (vs. non-insomnia HR 1.24, 95% CI: 1.00-1.54, P = 0.05), but not amongst short sleepers (<7 h). Short sleep duration also did not further inflate the risk of dementia amongst insomniacs. CONCLUSION: Insomnia and short sleep duration increase the risk of dementia amongst middle-aged to older adults.

Sleepiness, sleep duration, and human social activity: An investigation into bidirectionality using longitudinal time-use data.

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.

Disturbed sleep and its attribution to stress and other causes: A population-based survey.

This study explores the prevalence of attributed causes of disturbed sleep and the association between stress-disturbed sleep and age, sex, and sleep duration on weekdays as well as weekends in a representative sample. A nationally representative sample (n = 1,128, response rate 72.8%), stratified for sex and age, completed a computer-assisted phone survey that included questions about sleep disturbances and attributed causes. Stress was the main attributed cause of sleep disturbance (35.1%), most frequently attributed by younger women (χ2 = 26.5, p < 0.001). Prevalence of stress-disturbed sleep was higher with lower age (B = -0.05, odds ratio (OR) = 0.94, CI = 0.91, 0.98). There was a trend, however, toward a significant interaction between age and sex, with women in the older age-groups more frequently reporting stress-disturbed sleep than older men (B = -0.02, OR = 1.022, CI = 1.003, 1.042). Weekday sleep duration decreased with increased stress-disturbed sleep, with an inverse relationship on weekends except for those reporting stress-disturbed sleep more than 5 days per week (F = 10.5, p < 0.001), who also had the shortest weekend sleep duration. Sleep disturbances were commonly attributed to stress, and more strongly so in women younger than 46 years. Stress-disturbed sleep during weekdays seems to be potentially compensated for with extended sleep on weekends, except for those with continuous stress-disturbed sleep.

Insomnia in Tourette Syndrome and Chronic Tic Disorder.

BACKGROUND: Insomnia is common in Tourette syndrome (TS) and chronic tic disorder (CTD), but precise prevalence estimates are lacking. OBJECTIVE: In this Swedish register-based cohort study, we estimated the prevalence of insomnia in TS/CTD and quantified the magnitude of this association, accounting for familial confounders and relevant somatic and psychiatric comorbidities. METHODS: Of 10,444,702 individuals living in Sweden during the period from 1997 to 2013, 5877 had a diagnosis of TS/CTD and were compared to unexposed individuals from the general population on the presence of insomnia using logistic regression models. RESULTS: Individuals with TS/CTD had a period prevalence of insomnia of 32.16%, compared to 13.70% of the unexposed population. This translated into a 6.7-fold increased likelihood of insomnia in TS/CTD (odds ratio adjusted [aOR] for sex, birth year, birth country, and somatic disorders = 6.74; 95% confidence interval [CI], 6.37-7.15). A full sibling comparison, designed to adjust for shared familial factors, attenuated the estimates (aOR = 5.41; 95% CI, 4.65-6.30). When individuals with attention-deficit/hyperactivity disorder (ADHD) and pervasive developmental disorders were excluded, the association was also attenuated, whereas exclusion of other psychiatric comorbidities had minimal impact. Having persistent TS/CTD, comorbid ADHD, and taking ADHD medication greatly increased the likelihood of insomnia. CONCLUSIONS: Insomnia is significantly associated with TS/CTD, independently from somatic disorders, familial factors or psychiatric comorbidities, although familial factors, neurodevelopmental comorbidities, and ADHD/ADHD medication may explain part of the association. Insomnia should be routinely assessed and managed in TS/CTD, particularly in chronic patients and in those with comorbid ADHD. Other sleep disorders require further study. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Sleep duration and mortality, influence of age, retirement, and occupational group.

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.

Shiftworkers' attitude to their work hours, positive or negative, and why?

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.

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.

Relationship between sleep characteristics and markers of inflammation in Swedish women from the general population.

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 α (TNFα). 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 lnTNFα) 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 (ß = 0.11; 95% confidence interval [CI] = 0.02; 0.21), but not with lnIL-6 and lnTNFα. 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: ß = 0.71; 95% CI = 0.17; 1.24. ß = 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: ß = -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 TNFα. 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.

Fatigue and sleepiness responses to experimental inflammation and exploratory analysis of the effect of baseline inflammation in healthy humans.

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.

Short- and long-term mortality following hypnotic use.

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.

The impact of driver sleepiness on fixation-related brain potentials.

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.

Reciprocal relations between work stress and insomnia symptoms: A prospective study.

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.

Prospective study of job stress and risk of infections in Swedish adults.

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.

Sleep disturbance and work-related mental strain: A national prospective cohort study of the prediction of subsequent long-term sickness absence, disability pension and mortality.

Aims: Sleep disturbances and work-related mental strain are linked to increased sickness absence and disability pension (DP), but we have no information on synergy effects. The aim of this study was to examine the combined (and separate) association of the two predictors with subsequent long-term work disability and mortality. Methods: A total of 45,498 participants aged 16-64 years were interviewed in the Swedish Surveys of Living Conditions between 1997 and 2013, and were followed up on long-term sickness absence (LTSA; >90 days/year), DP and mortality via national registers until 2016. Crude and multivariable Cox analyses were used to estimate hazard ratios (HR) and 95% confidence intervals (CI). Results: For LTSA, the HRs for sleep disturbances and work-related mental strain were 1.6 (95% CI 1.5-1.7) and 1.3 (95% CI 1.2-1.4), respectively. For DP, the HRs were 2.0 (95% CI 1.8-2.2) and 1.4 (95% CI 1.2-1.5). Mortality was only predicted by sleep disturbances (HR=1.2, 95% CI 1.1-1.4). No synergy effect was seen. Conclusions: Work-related mental strain and, in particular, sleep disturbances were associated with a higher risk of subsequent LTSA and DP, but without synergy effects. Sleep disturbances were also associated with mortality. Exposure to interventions tackling sleep disturbance and prevention of workplace stress may reduce work disability.

Effects of evening exposure to electromagnetic fields emitted by 3G mobile phones on health and night sleep EEG architecture.

Studies on sleep after exposure to radiofrequency electromagnetic fields have shown mixed results. We investigated the effects of double-blind radiofrequency exposure to 1,930-1,990 MHz, UMTS 3G signalling standard, time-averaged 10 g specific absorption rate of 1.6 W kg-1 on self-evaluated sleepiness and objective electroencephalogram architecture during sleep. Eighteen subjects aged 18-19 years underwent 3.0 hr of controlled exposure on two consecutive days 19:45-23:00 hours (including 15-min break); active or sham prior to sleep, followed by full-night 7.5 hr polysomnographic recordings in a sleep laboratory. In a cross-over design, the procedure was repeated a week later with the second condition. The results for sleep electroencephalogram architecture showed no change after radiofrequency exposure in sleep stages compared with sham, but power spectrum analyses showed a reduction of activity within the slow spindle range (11.0-12.75 Hz). No differences were found for self-evaluated health symptoms, performance on the Stroop colour word test during exposure or for sleep quality. These results confirm previous findings that radiofrequency post-exposure in the evening has very little influence on electroencephalogram architecture but possible on spindle range activity.

Short sleep-poor sleep? A polysomnographic study in a large population-based sample of women.

There is a lack of studies on the association between total sleep time (TST) and other polysomnographical parameters. A key question is whether a short sleep is an expression of habitual short sleep, or whether it reflects temporary impairment. The purpose of the present study was to investigate the association between TST and amount of sleep stages and sleep continuity measures, in a large population-based sample of women (n = 385), sleeping at home in a normal daily life setting. The results show that sleep efficiency, N1 (min), N2 (min), REM (min), REM% and proportion of long sleep segments, increased with increasing TST, whereas the number of awakenings/hr, the number of arousals/hr, N1% and REM intensity decreased. In addition, longer sleep was more associated with TST being perceived as of "usual" duration and with better subjective sleep quality. TST was not associated with habitual reported sleep duration. It was concluded that short TST of a recorded sleep in a real-life context may be an indicator of poor objective sleep quality for that particular sleep episode. Because individuals clearly perceived this reduction, it appears that self-reports of poor sleep quality often may be seen as indicators of poor sleep quality. It is also concluded that PSG-recorded sleep duration does not reflect habitual reported sleep duration in the present real-life context.

Effect of sleep deprivation on emotional working memory.

The emotional dysregulation and impaired working memory found after sleep loss can have severe implications for our daily functioning. Considering the intertwined relationship between emotion and cognition in stimuli processing, there could be further implications of sleep deprivation in high-complex emotional situations. Although studied separately, this interaction between emotion and cognitive processes has been neglected in sleep research. The aim of the present study was to investigate the effect of 1 night of sleep deprivation on emotional working memory. Sixty-one healthy participants (mean age: 23.4 years) were either sleep deprived for 1 night (n = 30) or had a normal night's sleep (n = 31). They performed an N-back task with two levels of working memory load (1-back and 3-back) using positive, neutral and negative picture scenes. Sleep deprivation, compared with full night sleep, impaired emotional working memory accuracy, but not reaction times. The sleep-deprived participants, but not the controls, responded faster to positive than to negative and neutral pictures. The effect of sleep deprivation was similar for both high and low working memory loads. The results showed that although detrimental in terms of accuracy, sleep deprivation did not impair working memory speed. In fact, our findings indicate that positive stimuli may facilitate working memory processing speed after sleep deprivation.