High risk of near-crash driving events following night-shift work

Night-shift workers are at high risk of drowsiness-related motor vehicle crashes as a result of circadian disruption and sleep restriction. However, the impact of actual night-shift work on measures of drowsiness and driving performance while operating a real motor vehicle remains unknown. Sixteen night-shift workers completed two 2-h daytime driving sessions on a closed driving track at the Liberty Mutual Research Institute for Safety: (i) a postsleep baseline driving session after an average of 7.6 ± 2.4 h sleep the previous night with no night-shift work, and (ii) a postnight-shift driving session following night-shift work. Physiological measures of drowsiness were collected, including infrared reflectance oculography, electroencephalography, and electrooculography. Driving performance measures included lane excursions, near-crash events, and drives terminated because of failure to maintain control of the vehicle. Eleven near-crashes occurred in 6 of 16 postnight-shift drives (37.5%), and 7 of 16 postnight-shift drives (43.8%) were terminated early for safety reasons, compared with zero near-crashes or early drive terminations during 16 postsleep drives (Fishers exact: P = 0.0088 and P = 0.0034, respectively). Participants had a significantly higher rate of lane excursions, average Johns Drowsiness Scale, blink duration, and number of slow eye movements during postnight-shift drives compared with postsleep drives (3.09/min vs. 1.49/min; 1.71 vs. 0.97; 125 ms vs. 100 ms; 35.8 vs. 19.1; respectively, P < 0.05 for all). Night-shift work increases driver drowsiness, degrading driving performance and increasing the risk of near-crash drive events. With more than 9.5 million Americans working overnight or rotating shifts and one-third of United States commutes exceeding 30 min, these results have implications for traffic and occupational safety.

Social Jetlag, Chronotype, and Cardiometabolic Risk

CONTEXT

Shift work, which imposes a habitual disruption in the circadian system, has been linked to increased incidence of cardiometabolic diseases, and acute circadian misalignment alters various metabolic processes. However, it remains unclear whether day-to-day circadian dysregulation contributes to these risks beyond poor sleep and other behavioral characteristics.

OBJECTIVE

Individuals differ in circadian phase preference, known as chronotype, but may be constrained by modern work obligations to specific sleep schedules. Individuals experience social jetlag (SJL) due to a habitual discrepancy between their endogenous circadian rhythm and actual sleep times imposed by social obligations. Here, we examined whether chronotype and/or SJL associate with components of cardiovascular disease risk beyond the known effects of sleep disturbances, poor health behaviors, and depressive symptomatology.

DESIGN

Participants were healthy, midlife adults who worked part- or full-time day shifts (n = 447; mean age, 42.7 [range, 30-54] y; 53% female; 83% white). Chronotype was assessed with the Composite Scale of Morningness. SJL was quantified as the difference (in minutes) between the midpoints of actigraphy-derived sleep intervals before work vs non-workdays.

RESULTS

Multiple regression analyses showed that SJL related to a lower high-density lipoprotein-cholesterol level, higher triglycerides, higher fasting plasma insulin, insulin resistance, and adiposity (P < .05), even after adjustment for subjective sleep quality, actigraphy-derived sleep characteristics, depressive symptomatology, and health behaviors. Evening chronotype associated with lower high-density lipoprotein-cholesterol after adjustment for covariates.

CONCLUSION

Our findings suggest that a misalignment of sleep timing is associated with metabolic risk factors that predispose to diabetes and atherosclerotic cardiovascular disease.

Circadian disorders of sleep in adolescence: impact of the multimedia

The teenage years are a period of particular vulnerability to the desynchronization of the biological clock. Beyond geneticfactors, puberty is associated with a significant delay in the circadian phase of sleep, responsible for increasing dificulties with sleep onset at night and thus with awakening in the morning. The prevalence of Delayed Sleep Phase Syndrome (DSPS) is high in the adolescent population, affecting up to 16 % of teenagers. As sleep needs remain remarkably stable, adolescent sleep phase delay causes chronic sleep depriva- tion and subsequently daytime fatigue or even excessive daytime sleepiness, and also metabolic disturbances, neurocognitive problems associated with decreased school perfor- mance, as well as mood disorders. Whereas genetic and biological factors have been investigated by a number of studies, research on social, cognitive-behavioural or psychological factors is still limited to date. Among the latte; the technological revolution of the past decades, most importantly exposure to screens- has significantly modied adolescent behavior. This article discusses the latest research on the complex interaction of these different factors. It focusses particularly on the impact of media use on circadian disorders of sleep in adolescence.

Sleep and need for recovery in shift workers: do chronotype and age matter?

This study examined associations of chronotype and age with shift-specific assessments of main sleep duration, sleep quality and need for recovery in a cross-sectional study among N = 261 industrial shift workers (96.6% male). Logistic regression analyses were used, adjusted for gender, lifestyle, health, nap behaviour, season of assessment and shift schedule. Shift workers with latest versus earliest chronotype reported a shorter sleep duration (OR 11.68, 95% CI 3.31-41.17) and more awakenings complaints (OR 4.84, 95% CI 4.45-11.92) during morning shift periods. No associations were found between chronotype, sleep and need for recovery during evening and night shift periods. For age, no associations were found with any of the shift-specific outcome measures. The results stress the importance of including the concept of chronotype in shift work research and scheduling beyond the concept of age. Longitudinal research using shift-specific assessments of sleep and need for recovery are needed to confirm these results.

PRACTITIONER SUMMARY

Chronotype seems to better explain individual differences in sleep than age. In view of ageing societies, it might therefore be worthwhile to further examine the application of chronotype for individualised shift work schedules to facilitate healthy and sustainable employment.

Sleep inertia, sleep homeostatic and circadian influences on higher-order cognitive functions

Sleep inertia, sleep homeostatic and circadian processes modulate cognition, including reaction time, memory, mood and alertness. How these processes influence higher-order cognitive functions is not well known. Six participants completed a 73-day-long study that included two 14-day-long 28-h forced desynchrony protocols to examine separate and interacting influences of sleep inertia, sleep homeostasis and circadian phase on higher-order cognitive functions of inhibitory control and selective visual attention. Cognitive performance for most measures was impaired immediately after scheduled awakening and improved during the first ~2-4 h of wakefulness (decreasing sleep inertia); worsened thereafter until scheduled bedtime (increasing sleep homeostasis); and was worst at ~60° and best at ~240° (circadian modulation, with worst and best phases corresponding to ~09:00 and ~21:00 hours, respectively, in individuals with a habitual wake time of 07:00 hours). The relative influences of sleep inertia, sleep homeostasis and circadian phase depended on the specific higher-order cognitive function task examined. Inhibitory control appeared to be modulated most strongly by circadian phase, whereas selective visual attention for a spatial-configuration search task was modulated most strongly by sleep inertia. These findings demonstrate that some higher-order cognitive processes are differentially sensitive to different sleep-wake regulatory processes. Differential modulation of cognitive functions by different sleep-wake regulatory processes has important implications for understanding mechanisms contributing to performance impairments during adverse circadian phases, sleep deprivation and/or upon awakening from sleep.

Depression and circadian typology

BACKGROUND

The relationship between circadian disruptions and depressive disorders is a topic of great interest in contemporary psychiatry. Circadian rhythms include all physiological processes displaying a period around 24 hours. Sleep/wake cycles, body temperature, hormone secretion and other functions are subjected to person's individual circadian rhythm. Circadian typology includes three chronotypes: morning, neither and evening. The aim of this study was to examine the chronobiological aspects of depression.

METHODS

This cross-sectional study aimed to determine circadian rhythmic expression in 60 patients suffering from depression. The patients were in remission and were treated as outpatients at the Department of Psychiatry of the University Hospital Center Zagreb. The data were compared to a control group consisting of 40 medical workers employed at the University Hospital Centre Zagreb. A self-report measure of circadian typology was utilized - the Morningness-Eveningness Questionnaire.

RESULTS

According to our findings, among depressed patients 35% were morning, 58.3% neither and 6.7% evening types. In the control group 46% were morning, 48% neither and 6.0% evening types. Depressed patients reported stronger morning fatigue. Further, they tended to go to sleep earlier and felt more tired earlier in the evening, and they were less prone to choosing morning periods for completing complex cognitive tasks.

CONCLUSION

This study supports the association between depression and some alterations in circadian rhythms of behavior and sleep. Depression may be considered as the consequence or trigger of circadian disturbances. However, both depression and circadian rhythm disturbances may have a common aetiology: a decreased cellular resilience associated with lower resistance to stressful events.

Effect of Sleep/Wake Cycle on Autonomic Regulation

OBJECTIVE

To evaluate the association between irregular sleep/wake cycle in shift workers and autonomic regulation.

STUDY DESIGN

Cross-sectional, analytical study.

PLACE AND DURATION OF STUDY

Dow University Hospital, Karachi, from August to November 2013.

METHODOLOGY

All healthcare providers working in rotating shifts making a total (n=104) were included. Instrument was an integrated questionnaire applied to assess autonomic regulation, taken from Kröz et al. on scoring criteria, ranging from 18 - 54, where higher rating signifies strong autonomic regulation, indicating a stable Autonomic Nervous System (ANS) and vice versa. Participants were interviewed and their response was recorded by the investigator. Influence of sleep misalignment was measured quantitatively to extract index of autonomic activity.

RESULTS

There was a reduced trend in autonomic strength amongst shift workers. The mean score obtained on the Autonomic Scale was 37.8 ± 5.9.

CONCLUSION

Circadian misalignment has an injurious influence on ANS which might be valuable in controlling autonomic dysfunction that leads to fatal triggers in rotating shift workers.

The relationship between sleep-wake cycle and cognitive functioning in young people with affective disorders

Although early-stage affective disorders are associated with both cognitive dysfunction and sleep-wake disruptions, relationships between these factors have not been specifically examined in young adults. Sleep and circadian rhythm disturbances in those with affective disorders are considerably heterogeneous, and may not relate to cognitive dysfunction in a simple linear fashion. This study aimed to characterise profiles of sleep and circadian disturbance in young people with affective disorders and examine associations between these profiles and cognitive performance. Actigraphy monitoring was completed in 152 young people (16–30 years; 66% female) with primary diagnoses of affective disorders, and 69 healthy controls (18–30 years; 57% female). Patients also underwent detailed neuropsychological assessment. Actigraphy data were processed to estimate both sleep and circadian parameters. Overall neuropsychological performance in patients was poor on tasks relating to mental flexibility and visual memory. Two hierarchical cluster analyses identified three distinct patient groups based on sleep variables and three based on circadian variables. Sleep clusters included a ‘long sleep’ cluster, a ‘disrupted sleep’ cluster, and a ‘delayed and disrupted sleep’ cluster. Circadian clusters included a ‘strong circadian’ cluster, a ‘weak circadian’ cluster, and a ‘delayed circadian’ cluster. Medication use differed between clusters. The ‘long sleep’ cluster displayed significantly worse visual memory performance compared to the ‘disrupted sleep’ cluster. No other cognitive functions differed between clusters. These results highlight the heterogeneity of sleep and circadian profiles in young people with affective disorders, and provide preliminary evidence in support of a relationship between sleep and visual memory, which may be mediated by use of antipsychotic medication. These findings have implications for the personalisation of treatments and improvement of functioning in young adults early in the course of affective illness.

Glucocorticoids entrain molecular clock components in human peripheral cells

In humans, shift work induces a desynchronization between the circadian system and the outside world, which contributes to shift work-associated medical disorders. Using a simulated night shift experiment, we previously showed that 3 d of bright light at night fully synchronize the central clock to the inverted sleep schedule, whereas the peripheral clocks located in peripheral blood mononuclear cells (PBMCs) took longer to reset. This underlines the need for testing the effects of synchronizers on both the central and peripheral clocks. Glucocorticoids display circadian rhythms controlled by the central clock and are thought to act as synchronizers of rodent peripheral clocks. In the present study, we tested whether the human central and peripheral clocks were sensitive to exogenous glucocorticoids (Cortef) administered in the late afternoon. We showed that 20 mg Cortef taken orally acutely increased PER1 expression in PBMC peripheral clocks. After 6 d of Cortef administration, the phases of central markers were not affected, whereas those of PER2-3 and BMAL1 expression in PBMCs were shifted by ∼ 9.5-11.5 h. These results demonstrate, for the first time, that human peripheral clocks are entrained by glucocorticoids. Importantly, they suggest innovative interventions for shift workers and jet-lag travelers, combining synchronizing agents for the central and peripheral clocks.

[Time to sleep; disruption of the biological clock due to night and shift work]

Now that the 24-hour economy is putting an ever-increasing mark on social life, the effects of the disruption of natural biological rhythms are becoming clearer. In addition to its effects on sleep, this article discusses its long-term health effects. Potential measures to reduce and counteract the adverse effects of working night shifts on general well-being, sleep and health are summarized; the roles of light and rhythm are explored. Further research into the health effects of working nights and unsociable shift patterns is indicated.

Determinants of altered sleep-wake rhythmicity in patients treated for nonfunctioning pituitary macroadenomas

CONTEXT AND OBJECTIVE

In a cohort of 17 patients treated for nonfunctioning pituitary macroadenoma (NFMA), we observed alterations in polysomnographic sleep characteristics and actigraphic sleep-wake rhythmicity, and subjective fatigue, daytime somnolence, and low sleep quality. We aimed to confirm the actigraphic data in a larger scale cohort of NFMA patients, powered to address risk factors for altered rhythmicity, including the effects of hydrocortisone replacement.

METHODS

Sleep-wake rhythmicity in treated NFMA patients was measured using actigraphy for 7 days, and subjective sleep quality and quality of life (QoL) with validated questionnaires. To assess the influence of hydrocortisone dependency, we additionally studied patients with Addison's disease (AD). The results were compared with matched healthy controls.

RESULTS

We included 69 NFMA patients in long-term remission after trans-sphenoidal surgery on stable replacement therapy for hypopituitarism, 21 AD patients, and 58 controls. NFMA patients reported severely impaired QoL, sleep quality, and increased daytime sleepiness. The day-night dichotomy of activity was fragmented, with decreased daytime activity and a tendency for increased nighttime activity. Preoperative visual field defects (VFD) were associated with this fragmentation, and vasopressin deficiency with decreased sleep efficiency, independent of age, hypopituitarism, or radiotherapy. AD patients showed similar decreases in daytime functioning, but normal subjective and objective sleep, and no daytime sleepiness.

CONCLUSION

NFMA patients suffer from altered sleep-wake rhythmicity. Hydrocortisone dependency may explain part of the decreased daytime functioning, but the independent influence of VFD and differences between AD and NFMA patients point towards a role for dysfunction of the adjacent suprachiasmatic nucleus (SCN).

[24-hour work: the interaction of stress and changes in the sleep-wake cycle in the police force]

Disruption in police officers. In recent years there has been a widespread growth in services, available regardless of time or day organization (24/7 service) and a diffuse increase in their use, both in work and private lives, generally ignoring the importance of a regular sleep organization. Police officers - often need to work extended shifts and long hours under highly stressful conditions, which results in reduced levels of safety and operational effectiveness. In numerous studies, perceived stress has been found to correlate with both subjective and objective disturbances in sleep. Consequently, excessive daytime sleepiness is one of the most frequent health and safety hazards that police officers have to deal with. Sleep deprivation affects performance outcomes through a wide range of cognitive domains. Sleepiness and fatigue, caused by sleep loss, extended work and wakefulness, circadian misalignment and sleep disorders are major causes of workplace human errors, incidents, and accidents. Therefore, prevention of sleep loss, high levels of stress and fatigue is a key factor to consider when assessing emergency intervention. In order to combat fatigue and sleepiness, a 30-90 minutes nap before night shift could be a viable option.

Shift work and employee fatigue: implications for occupational health nursing

Long work hours and irregular shifts are part of the nation's 24-hour society and contribute to employee fatigue. Factors affecting employee fatigue are circadian rhythm, sleep quality and quantity, individual health, the environment, and work tasks. Employee fatigue contributes to accidents and injuries, and affects occupational performance, safety, and health. These findings should be used by occupational health nurses to address fatigue management and develop comprehensive fatigue management programs.

Chronobiology, cognitive function and depressive symptoms in surgical patients

Biological rhythms are essential for the regulation of many life processes. Disturbances of the circadian rhythm are known to affect human health, performance and well-being and the negative consequences are numerous and widespread. Cognitive dysfunction, fatigue, pain, sleep disturbances and mood disorders, such as anxiety and depression, are common problems arising around the time of surgery or in the course of a cancer diagnosis and subsequent treatment period. The importance of investigating prevention or treatment possibilities in these populations is significant due to the extent of the problems and the derived consequences on morbidity and mortality. Genetic predisposition to these problems is also an issue in focus. In this thesis we initially investigated whether the specific clock gene genotype PER(5/5) was associated with the development of postoperative cognitive dysfunction one week after non-cardiac surgery. We did not find any association, although this could have been due to the size of the study. Yet, if PER3(5/5) is associated with a higher incidence of postoperative cognitive dysfunction, the risk seems to be only modestly increased and by less than 10%. Melatonin is a hormone with well-known chronobiotic and hypnotic effects. In addition, exogenous melatonin is also known to have anxiolytic, analgesic, antidepressant and positive cognitive effects. Based on the lack of studies investigating these effects of melatonin, we conducted the MELODY trial in which we investigated the effect of 6 mg oral melatonin on depressive symptoms, anxiety, sleep, cognitive function and fatigue in patients with breast cancer in a three month time period after surgery. Melatonin had an effect on reducing the risk of developing depressive symptoms and also increased sleep efficiency perioperatively and total sleep time postoperatively. No effect was found on anxiety, sleep quality, sleepiness, general well-being or pain, however melatonin seemed to positively influence the ability to complete trial participation compared to placebo. Postoperative cognitive dysfunction was not a problem in this limited population. With regard to safety in our study, melatonin treatment for three months did not cause any serious adverse effects. Finally, we systematically reviewed the literature on the prophylactic or therapeutic effect of melatonin for depression or depressive symptoms in adult patients and assessed the safety of melatonin in these studies. The quantity, size and quality of trials investigating this question were not high and there was no clear evidence of an effect, although some studies were positive. In conclusion, further research is warranted with regard to the prophylactic effect and treatment effect of melatonin in depression, depressive symptoms, cognitive disturbances and symptom clusters of cancer patients in general. In addition, more hypothesis-generating studies with regard to the genetic heritability of POCD are needed.

Circadian regulation of metabolism

In association with sleep-wake and fasting-feeding cycles, organisms experience dramatic oscillations in energetic demands and nutrient supply. It is therefore not surprising that various metabolic parameters, ranging from the activity status of molecular energy sensors to circulating nutrient levels, oscillate in time-of-day-dependent manners. It has become increasingly clear that rhythms in metabolic processes are not simply in response to daily environmental/behavioral influences, but are driven in part by cell autonomous circadian clocks. By synchronizing the cell with its environment, clocks modulate a host of metabolic processes in a temporally appropriate manner. The purpose of this article is to review current understanding of the interplay between circadian clocks and metabolism, in addition to the pathophysiologic consequences of disruption of this molecular mechanism, in terms of cardiometabolic disease development.

Laparoscopic skills and cognitive function are not affected in surgeons during a night shift

OBJECTIVE

To monitor surgeons' performance and cognition during night shifts.

DESIGN

Surgeons were monitored before call and on call (17-hour shift). Psychomotor performance was assessed by laparoscopic simulation and cognition by the d2 test of attention. The surgeons performed the laparoscopic simulation and the d2 test of attention at 8 a.m. before call and at 4 a.m. on call. Sleep was measured by wrist actigraphy and sleepiness by the Karolinska sleepiness scale.

SETTING

Department of Surgery at Herlev Hospital, Denmark.

PARTICIPANTS

Overall, 30 interns, residents, and attending surgeons were included and completed the study. One participant was subsequently excluded owing to myxedema.

RESULTS

The surgeons slept significantly less on call than before call. There was increasing sleepiness on call; however, no significant differences were found in the precall laparoscopic simulation values compared with on-call values. The d2 test of attention showed significantly improved values on call compared with before call.

CONCLUSION

Sleep deprivation during a 17-hour night shift did not impair surgeons' psychomotor or cognitive performance.

Health impact of fasting in Saudi Arabia during Ramadan: association with disturbed circadian rhythm and metabolic and sleeping patterns

BACKGROUND

Muslims go through strict Ramadan fasting from dawn till sunset for one month yearly. These practices are associated with disturbed feeding and sleep patterns. We recently demonstrated that, during Ramadan, circadian cortisol rhythm of Saudis is abolished, exposing these subjects to continuously increased cortisol levels.

HYPOTHESIS

Secretory patterns of other hormones and metabolic parameters associated with cortisol, and insulin resistance, might be affected during Ramadan.

PROTOCOL

Ramadan practitioners (18 males, 5 females; mean age ±SEM = 23.16±1.2 years) were evaluated before and two weeks into Ramadan. Blood was collected for measurements of endocrine and metabolic parameters at 9 am (±1 hour) and again twelve hours later.

RESULTS

In Ramadan, glucose concentration was kept within normal range, with a significant increase in the morning. Mean morning concentration of leptin was significantly higher than pre-Ramadan values (p = 0.001), in contrast to that of adiponectin, which was significantly lower (p<0.001). These changes were associated with increased insulin resistance in morning and evening. Concentrations of hsCRP were lower during Ramadan than those during regular living conditions, however, normal circadian fluctuation was abolished (p = 0.49). Even though means of liver enzymes, total bilirubin, total protein and albumin were all decreased during Ramadan, statistically lower means were only noted for GGT, total protein, and albumin (p = 0.018, 0.002 and 0.001 respectively).

DISCUSSION

Saudi Ramadan practitioners have altered adipokine patterns, typical of insulin resistance. The noted decreases of hsCRP, liver enzymes, total protein, and albumin, are most likely a result of fasting, while loss of circadian rhythmicity of hsCRP is probably due to loss of circadian cortisol rhythm.

CONCLUSIONS

Modern Ramadan practices in Saudi Arabia, which are associated with evening hypercortisolism, are also characterized by altered adipokines patterns, and an abolished hsCRP circadian rhythm, all likely to increase cardiometabolic risk.

Sleep and circadian rhythm regulation in early Parkinson disease

IMPORTANCE

Sleep disturbances are recognized as a common nonmotor complaint in Parkinson disease but their etiology is poorly understood.

OBJECTIVE

To define the sleep and circadian phenotype of patients with early-stage Parkinson disease.

DESIGN, SETTING, AND PARTICIPANTS

Initial assessment of sleep characteristics in a large population-representative incident Parkinson disease cohort (N=239) at the University of Cambridge, England, followed by further comprehensive case-control sleep assessments in a subgroup of these patients (n=30) and matched controls (n=15).

MAIN OUTCOMES AND MEASURES

Sleep diagnoses and sleep architecture based on polysomnography studies, actigraphy assessment, and 24-hour analyses of serum cortisol, melatonin, and peripheral clock gene expression (Bmal1, Per2, and Rev-Erbα).

RESULTS

Subjective sleep complaints were present in almost half of newly diagnosed patients and correlated significantly with poorer quality of life. Patients with Parkinson disease exhibited increased sleep latency (P = .04), reduced sleep efficiency (P = .008), and reduced rapid eye movement sleep (P = .02). In addition, there was a sustained elevation of serum cortisol levels, reduced circulating melatonin levels, and altered Bmal1 expression in patients with Parkinson disease compared with controls.

CONCLUSIONS AND RELEVANCE

Sleep dysfunction seen in early Parkinson disease may reflect a more fundamental pathology in the molecular clock underlying circadian rhythms.

Sleep duration and incidence of lung cancer in ageing men

BACKGROUND

Previous studies have suggested an association between sleep duration and cancer. However, the information on sleep duration regard to risk of lung cancer is scanty.

METHODS

Analysed data comprised prospective population-based cohort of 2586 men (aged 42-60 years) from Eastern Finland. Baseline survey and clinical examinations took place 1984-1989, and diagnosed lung cancers were obtained until the end of 2011 through linkage with the Finnish Cancer Registry. Self-reported sleep was categorized as ≤6.5 h, 7-7.5 h, and ≥8 h. Subjects with prior history of cancer or psychotropic medication (hypnotics or sedatives) were excluded from the analyses. Cox proportional hazards models with adjustments for possible confounders were used to examine the association.

RESULTS

Significant association between sleep duration and increased lung cancer risk was observed after adjustments for age, examination years, cumulative smoking history, family cancer history and Human Population Laboratory Depression scale scores (HR 2.12, 95% CI 1.17-3.85 for ≤6.5 h sleep, and HR 1.88, 95% CI 1.09-3.22 for ≥8 h sleep). Associations were even stronger among current smokers (HR 2.23, 95% CI 1.14-4.34 for ≤6.5 h sleep, and HR 2.09, 95% CI 1.14-3.81 for ≥8 h sleep). After further adjustments for alcohol consumption, physical activity, body mass index, marital status, education years, night work, employment status, asthma and chronic bronchitis, the association remained significant both in the whole study population and among smokers. When cumulative smoking history was replaced by current smoking in the adjustments, the increased risk was limited to those who slept<6.5 h.

CONCLUSIONS

Sleep duration of less than 7-7.5 hours or more than 7-7.5 hours associates with increased lung cancer risk. The physiological factors underlying the association are complex, and they may relate to melatonin excretion patterns, low-grade inflammation in cancer development process or disruptions in circadian rhythmicity.

[Orexin: clinical and therapeutic implications]

INTRODUCTION. Recent research has reported the existence of a new class of neuropeptides, called orexins or hypocretins, which are produced by a small group of neurons in the hypothalamus and whose actions are mediated by two types of receptors: OX1R and OX2R. More specifically, the orexinergic neurons have been located exclusively in cells in the lateral, dorsomedial and perifornical areas of the hypothalamus. Despite this highly specific anatomical origin, the orexinergic neurons are projected widely into a number of brainstem, cortical and limbic regions. DEVELOPMENT. This fuzzy pattern of distribution of the orexinergic fibres would be indicating the involvement of this peptidic system in a wide range of functions; indeed, it has been related with the mechanisms that enable regulation of the sleep-wake cycle, the ingestion of food and drink, and some particular types of learning, such as learning certain preferences regarding tastes. It has also been suggested that upsets in the functioning of the orexinergic system would explain the appearance of certain clinical disorders like narcolepsy, obesity or addiction to drug of abuse. CONCLUSIONS. Further research will help to determine the functioning of orexinergic neurons and the interaction between the systems that regulate emotion, energetic homeostasis and the reward mechanisms, on the one hand, and the systems that regulate the sleep-wake cycle on the other. That knowledge would almost certainly make it possible to develop new drugs that, by acting upon the orexinergic system, would be effective in the treatment of sleep disorders such as insomnia or narcolepsy, eating disorders or drug addiction.

Changes of physiological functions induced by shift work

Shift work was positively associated with higher incidence of metabolic syndrome, obesity, cardiovascular disease, sleep disturbances, decreased immune functions, and cancer. Observed disorders were manifested usually after longer time of shift work (more than 10 years). On the other hand, disturbed daily profile of melatonin and cortisol during shift work were detected even in human self reporting well tolerated shift work. Similarly, changes in thyroid stimulating hormone, prolactin, growth hormone, insulin, and ghrelin were demonstrated. Changes in hormone concentrations are influenced by shift work, sleep or circadian system or combinations of above mentioned regulatory factors. The circadian system consists of the central part localized in the hypothalamus and peripheral oscillators located in all tissues of the body. The central oscillator is predominantly synchronized by light and peripheral oscillators are more responsive to metabolic signals. Under conditions of shift work, central and peripheral oscillators dissociate that causes misalignment of daily rhythms in physiological functions. Synchronization during shift work can be improved by melatonin supplementation and manipulation with light:dark cycles and food regimens. Shift work tolerance is individual. Partial positive selection can be achieved on the basis of several psychological traits. Appropriate schedule can be estimated on the basis of chronotype.