Digital cognitive behavioural therapy for insomnia reduces insomnia in nurses suffering from shift work disorder: A randomised-controlled pilot trial.

Insomnia is a primary symptom of shift work disorder, yet it remains undertreated. This randomised-controlled pilot trial examined the efficacy of a digital, guided cognitive behavioural therapy for insomnia adapted to shift work (SleepCare) in nurses with shift work disorder. The hypothesis was that SleepCare reduces insomnia severity compared with a waitlist control condition. A total of 46 unmedicated nurses suffering from shift work disorder with insomnia (age: 39.7 ± 12.1 years; 80.4% female) were randomised to the SleepCare group or the waitlist control group. The primary outcome measure was the Insomnia Severity Index. Other questionnaires on sleep, mental health and occupational functioning, sleep diary data and actigraphy data were analysed as secondary outcomes. Assessments were conducted before (T0), after the intervention/waitlist period (T1), and 6 months after treatment completion (T2). The SleepCare group showed a significant reduction in insomnia severity from T0 to T1 compared with the control condition (ß = -4.73, SE = 1.12, p < 0.001). Significant improvements were observed in sleepiness, dysfunctional beliefs about sleep, pre-sleep arousal, sleep effort, self-reported sleep efficiency and sleep onset latency. No significant effect was found in actigraphy data. Depressive and anxiety symptoms, cognitive irritation and work ability improved significantly. Overall, satisfaction and engagement with the intervention was high. SleepCare improved insomnia severity, sleep, mental health and occupational functioning. This is the first randomised-controlled trial investigating the efficacy of digital cognitive behavioural therapy for insomnia in a population suffering from shift work disorder with insomnia. Future research should further explore these effects with larger sample sizes and active control conditions.

Acceptance and Commitment Therapy, Combined with Bedtime Restriction, versus Cognitive Behavioral Therapy for Insomnia: A Randomized Controlled Pilot Trial.

INTRODUCTION: Cognitive behavioral therapy for insomnia (CBT-I) is the current first-line treatment for insomnia. However, rates of nonresponse and nonremission are high and effects on quality of life are only small to moderate, indicating a need for novel treatment developments. We propose that Acceptance and Commitment Therapy (ACT) addresses core pathophysiological pathways of insomnia. ACT therefore has the potential to improve treatment efficacy when combined with bedtime restriction, the most effective component of CBT-I. The aim of this study was to compare the efficacy of ACT for insomnia combined with bedtime restriction (ACT-I) and CBT-I in improving insomnia severity and sleep-related quality of life. METHODS: Sixty-three patients with insomnia disorder (mean age 52 years, 65% female, 35% male) were randomly assigned to receive either ACT-I or CBT-I in a group format. The primary outcomes were insomnia severity (Insomnia Severity Index) and sleep-related quality of life (Glasgow Sleep Impact Index). Outcomes were assessed before randomization (T0), directly after treatment (T1), and at 6-month follow-up (T2). RESULTS: The results indicated significant, large pre-to-post improvements in both groups, for both primary and secondary outcomes. Improvements were maintained at the 6-month follow-up. However, there was no significant group by time interactions in linear mixed models, indicating an absence of differential efficacy. On a subjective treatment satisfaction scale, patients in the ACT-I group indicated significantly greater satisfaction with their improvement of several aspects of health including their energy level and work productivity. CONCLUSIONS: The results suggest that ACT-I is feasible and effective, but not more effective than CBT-I for the improvement of insomnia severity and sleep-related quality of life. Future studies are needed to assess whether ACT-I is noninferior to CBT-I and to shed light on mechanisms of change in both treatments.

Interactions between insomnia, sleep duration and emotional processes: An ecological momentary assessment of longitudinal influences combining self-report and physiological measures.

Previous studies indicated that further investigation is needed to understand how insomnia disorder interacts with emotional processes. The present study is an ecological momentary assessment evaluating the link between emotional and sleep alterations in patients with insomnia. Physiological (heart rate and heart rate variability) and subjective (sleep and emotions) indices were observed for 5 days in patients with insomnia disorder (n = 97), good sleepers under self-imposed sleep restriction (n = 41), and good sleepers with usual amount of sleep (n = 45). We evaluated differences in emotion regulation strategies and in valence and variability of emotional experiences. Over 5 days, patients with insomnia showed increased sleep and emotional difficulties compared with both control groups. Independent from group allocation, days with more negative emotions were associated with higher sleep alterations. Longer wake episodes at night and higher diurnal heart rate were associated with increased variations in emotion experienced during the day. Only in patients with insomnia, use of adaptive emotion regulation strategies was associated with higher sleep efficiency. Our data showed that alterations in sleep and emotional processes are closely linked. A combination of strategies targeting both sleep and emotional processes appears promising in the prevention and treatment of insomnia disorder.

Personality and insomnia: A systematic review and narrative synthesis.

The inherent nature of personality serves as a predisposing, and possible maintaining, factor of insomnia. However, methodological differences limit the ability to draw causal conclusions regarding the specific traits involved in the aetiology of the disorder. This systematic review of the relationship between insomnia and personality provides a narrative synthesis of the literature to date. Here, we identified N = 76 studies meeting the inclusion/exclusion criteria. The outcomes reliably evidenced the experience of insomnia to be associated with personality traits that are typically considered to be negative or maladaptive in nature. More specifically, insomnia was related to neuroticism, introversion, perfectionistic doubts and concerns, elevated personal standards, negative affect, social inhibition and avoidance, hysteria, hypochondriasis, psychasthenia, impulsive behaviour, anger, hostility, and psychopathic tendencies, schizotypal and borderline traits, reduced conscientiousness and self-directedness, and negatively perceived perception of the self. Several studies examined the role that personality plays in predicting the treatment efficacy and adherence of CBTi. Moving forward, longitudinal research, methodological consistency, the mediating role of treatment outcomes and adherence, and clinical and population representative samples should be prioritised. Methodological strengths and limitations of the literature are discussed alongside the next steps that should be taken to advance our understanding of the literature.

Adherence to sleep restriction therapy - An evaluation of existing measures.

Sleep restriction, a key element of cognitive behavioural therapy for insomnia, involves considerable behavioural changes in patients' lives, leading to side-effects like increased daytime sleepiness. Studies on sleep restriction rarely report adherence, and when assessed it is often limited to the average number of therapy sessions attended. This study aims to systematically evaluate different measures of adherence to cognitive behavioural therapy for insomnia and their relationship with treatment outcome. This is a secondary analysis of data from a randomized controlled trial investigating cognitive behavioural therapy for insomnia (Johann et al. (2020) Journal of Sleep Research, 29, e13102). The sample included 23 patients diagnosed with insomnia according to DSM-5 criteria who underwent 8 weeks of cognitive behavioural therapy for insomnia. The following adherence measures based on sleep diary data were used: number of sessions completed; deviations from agreed time in bed; average percentage of patients deviating from bedtime by 15, 30 or 60 min; variability of bedtime and wake-up time; change in time in bed from pre- to post-assessment. Treatment outcome was assessed using the Insomnia Severity Index. Multiple regression models were employed, and insomnia severity was controlled for. Results showed that none of the adherence measures predict insomnia severity. Baseline insomnia severity, dysfunctional thoughts and attitudes about sleep, depression or perfectionism did not predict adherence. The limited variance in the outcome parameter due to most patients benefiting from treatment and the small sample size may explain these findings. Additionally, using objective measures like actigraphy could provide a better understanding of adherence behaviour. Lastly, the presence of perfectionism in patients with insomnia may have mitigated adherence problems in this study.

The Effects of Cognitive Behavioral Therapy for Insomnia on Multidimensional Perfectionism.

Perfectionism is related to insomnia and objective markers of disturbed sleep. This study examined whether multidimensional perfectionism is related to dysfunctional beliefs about sleep, sleep-effort, pre-sleep arousal, and polysomnography-determined markers of sleep among individuals with insomnia. The effects of cognitive behavioral therapy for insomnia (CBT-I) on perfectionism was also examined. This was a secondary analysis of a randomized controlled trial on CBT-I. Forty-three insomnia patients were randomized to treatment (receiving CBT-I) or waitlist control groups. Sleep was recorded using polysomnography at baseline. Participants completed measures of perfectionism, dysfunctional beliefs about sleep, sleep-effort and pre-sleep arousal at baseline and posttreatment. Total perfectionism scores and doubts about action, concern over mistakes and personal standards were each significantly related to increased sleep effort, pre-sleep arousal and dysfunctional beliefs about sleep at baseline. Patients receiving treatment displayed increased total perfectionism scores posttreatment d = .49. In those receiving treatment, levels of organization d = .49 and parental expectations d = .47 were significantly increased posttreatment, relative to baseline. In line with the literature, our results confirm that perfectionism is related to insomnia. Here, insomnia was related to increased sleep effort, pre-sleep arousal and dysfunctional beliefs about sleep. The propensity to maintain a high standard of order and organization may be elevated following CBT-I, considering the treatment protocol expects patients to strictly adhere to a set of clearly defined rules. Levels of parental expectations may be increased following CBT-I since the patient-therapist-relationship may trigger implicit expectations in patients which are reminiscent of their relationship to their parents.

How many hours do you sleep? A comparison of subjective and objective sleep duration measures in a sample of insomnia patients and good sleepers.

Our objective was to assess the agreement and linear relationships amongst multiple measures of sleep duration in a sample of patients with insomnia disorder and good sleeper controls. We retrospectively analysed data from 123 patients with insomnia disorder and 123 age- and gender-matched good sleeper controls who completed a simple subjective habitual sleep duration question (Pittsburgh Sleep Quality Index), a sleep diary (5-14 days), 2 nights of polysomnography, and two corresponding morning subjective estimates of sleep duration. Descriptive statistics, linear regression analyses and Bland-Altman plots were used to describe the relationship and (dis)agreement between sleep duration measures. Relationships between polysomnography and the simple question as well as between polysomnography and sleep diary were weak to non-existent. Subjective measures and polysomnography did not agree. Sleep duration measured with the Pittsburgh Sleep Quality Index or sleep diary was about 2 hr above or up to 4 hr below polysomnography-measured sleep duration. Patients with insomnia disorder, on average, reported shorter sleep duration compared with polysomnography, while good sleeper controls, on average, reported longer sleep duration compared with polysomnography. The results suggest that subjective and objective measures apparently capture different aspects of sleep, even when nominally addressing the same value (sleep duration). They disagree in both patients with insomnia disorder and good sleeper controls, but in different directions. Studies assessing sleep duration should take into account both the investigated population and the assessment method when interpreting results. Future studies should continue to investigate possible psychological and physiological correlates of sleep (mis)perception.

Multidimensional perfectionism and poor sleep: A meta-analysis of bivariate associations.

The link between perfectionism and poor sleep has been intensively debated, and previous studies on perfectionism-sleep associations have yielded mixed results. Recent research suggests that the two-dimensional perfectionism model, differentiating perfectionistic concerns (centered around concerns over imperfections) and perfectionistic strivings (centered around excessively high personal standards), may reconcile previously inconclusive findings, as both dimensions might be differentially related to sleep. Thus, to clarify the perfectionism-sleep link, this meta-analysis investigated relations of perfectionistic concerns and strivings with two well-established self-report measures of poor sleep. A systematic literature search yielded 55 effect sizes from 15 studies (N = 10,275) for inclusion in this meta-analysis. Perfectionistic concerns correlated positively with the Insomnia Severity Index (r+ = 0.221, 95% CI [0.102, 0.333], p = .004) and the Pittsburgh Sleep Quality Index (r+ = 0.248, 95% CI [0.172, 0.321], p < .001). Perfectionistic strivings correlated positively, albeit less strongly, with the Insomnia Severity Index (r+ = 0.114, 95% CI [0.039, 0.189], p = .010), but not significantly with the Pittsburgh Sleep Quality Index (r+ = 0.028, 95% CI [-0.026, 0.082], p = .247). These meta-analytic findings indicate that perfectionistic concerns are substantially linked to poor sleep, whereas the relation of perfectionistic strivings with sleep is less evident. Although the identified associations were less robust for perfectionistic strivings than for perfectionistic concerns, previously used labels like "positive" or "adaptive" appear inappropriate for perfectionistic strivings in the context of sleep.

Insomnia disorder: State of the science and challenges for the future.

Insomnia disorder comprises symptoms during night and day that strongly affect quality of life and wellbeing. Prolonged sleep latency, difficulties to maintain sleep and early morning wakening characterize sleep complaints, whereas fatigue, reduced attention, impaired cognitive functioning, irritability, anxiety and low mood are key daytime impairments. Insomnia disorder is well acknowledged in all relevant diagnostic systems: Diagnostic and Statistical Manual of the American Psychiatric Association, 5th revision, International Classification of Sleep Disorders, 3rd version, and International Classification of Diseases, 11th revision. Insomnia disorder as a chronic condition is frequent (up to 10% of the adult population, with a preponderance of females), and signifies an important and independent risk factor for physical and, especially, mental health. Insomnia disorder diagnosis primarily rests on self-report. Objective measures like actigraphy or polysomnography are not (yet) part of the routine diagnostic canon, but play an important role in research. Disease concepts of insomnia range from cognitive-behavioural models to (epi-) genetics and psychoneurobiological approaches. The latter is derived from knowledge about basic sleep-wake regulation and encompass theories like rapid eye movement sleep instability/restless rapid eye movement sleep. Cognitive-behavioural models of insomnia led to the conceptualization of cognitive-behavioural therapy for insomnia, which is now considered as first-line treatment for insomnia worldwide. Future research strategies will include the combination of experimental paradigms with neuroimaging and may benefit from more attention to dysfunctional overnight alleviation of distress in insomnia. With respect to therapy, cognitive-behavioural therapy for insomnia merits widespread implementation, and digital cognitive-behavioural therapy may assist delivery along treatment guidelines. However, given the still considerable proportion of patients responding insufficiently to cognitive-behavioural therapy for insomnia, fundamental studies are highly necessary to better understand the brain and behavioural mechanisms underlying insomnia. Mediators and moderators of treatment response/non-response and the associated development of tailored and novel interventions also require investigation. Recent studies suggest that treatment of insomnia may prove to add significantly as a preventive strategy to combat the global burden of mental disorders.

Insomnia evaluation and treatment during peripartum: a joint position paper from the European Insomnia Network task force "Sleep and Women," the Italian Marcè Society and international experts task force for perinatal mental health.

Insomnia symptoms are frequent during peripartum and are considered risk factors for peripartum psychopathology. Assessing and treating insomnia and related conditions of sleep loss during peripartum should be a priority in the clinical practice. The aim of this paper was to conduct a systematic review on insomnia evaluation and treatment during peripartum which may be useful for clinicians. The literature review was carried out between January 2000 and May 2021 on the evaluation and treatment of insomnia during the peripartum period. The PubMed, PsycINFO, and Embase electronic databases were searched for literature published according to the PRISMA guidance with several combinations of search terms "insomnia" and "perinatal period" or "pregnancy" or "post partum" or "lactation" or "breastfeeding" and "evaluation" and "treatment." Based on this search, 136 articles about insomnia evaluation and 335 articles on insomnia treatment were found and we conducted at the end a narrative review. According to the inclusion/exclusion criteria, 41 articles were selected for the evaluation part and 22 on the treatment part, including the most recent meta-analyses and systematic reviews. Evaluation of insomnia during peripartum, as for insomnia patients, may be conducted at least throughout a clinical interview, but specific rating scales are available and may be useful for assessment. Cognitive behavioral therapy for insomnia (CBT-I), as for insomnia patients, should be the preferred treatment choice during peripartum, and it may be useful to also improve mood, anxiety symptoms, and fatigue. Pharmacological treatment may be considered when women who present with severe forms of insomnia symptoms do not respond to nonpharmacologic therapy.

Insomnia and poor sleep quality during peripartum: a family issue with potential long term consequences on mental health.

BACKGROUND: Improving maternal's health is a worldwide priority. Sleep is a fundamental operating state of the central nervous system and it may be one of the most important psychophysiological processes for brain function and mental health. The study of maternal sleep problem including insomnia, however, implies deepening our understanding of family context. Family systems are dynamic and involve reciprocal interactions among members during day and night. So far, however, maternal and children's sleep has been rarely studied in a family perspective, and paternal sleep has often been neglected. METHODS: The present work summarizes in a narrative review the state of the art of our current knowledge on the role of insomnia and poor quality of sleep for mental health in all family members in the peripartum period. The mother, the father, the child and the family interactive perspectives are considered. RESULTS: Insomnia and poor sleep problems are frequent in all family members during peripartum. Poor sleep and insomnia symptoms are recognized as important risk factors for mental health in adults and children. Despite this alarming evidence, sleep is rarely assessed in clinical contexts. CONCLUSIONS: Clinical implications include the utmost relevance of assessing sleep problems during pregnancy and early post-partum. Insomnia and poor sleep quality should be evaluated and treated in the clinical practice by using a "family perspective."

The Association between Diurnal Sleep Patterns and Emotions in Infants and Toddlers Attending Nursery.

BACKGROUND: Childcare programs often include mandatory naptime during the day. Loss of daytime sleep could lead to a moderate-to-large decrease in self-regulation, emotion processing, and learning in early childhood. Nevertheless, daytime sleep has been less accurately studied than nighttime sleep. This study aims to explore the relationship between diurnal sleep habits in nursery settings, nocturnal sleep quality, and post-nap emotional intensity in infants and toddlers. METHODS: Data of 92 children (52 girls, 40 boys) aged 6 to 36 months were obtained. Sleep habits as well as positive and negative emotions were monitored by educators during nursery times through a sleep and emotion diary for two weeks. RESULTS: Explorative analyses showed that diurnal sleep hours decreased across age groups (except for females aged 25-36 months) and that all age groups had a lower amount of nocturnal sleep than is recommended by the National Sleep Foundation. Partial correlation analysis showed significant correlation between daytime sleep onset latency and positive emotions. Mediation analyses showed that daytime napping is relevant for emotional functioning independently of nocturnal sleep quality. CONCLUSIONS: Daytime sleep in early childhood seems to be linked to the management of positive and negative emotions and could play a role in healthy development of emotional processes.

The efficacy of cognitive and behavior therapies for insomnia on daytime symptoms: A systematic review and network meta-analysis.

Insomnia disorder, defined by nocturnal and daytime symptoms, is highly prevalent worldwide and is associated with the onset of mental illness. Although daytime symptoms are often the reason insomnia patients seek help, it is not clear whether recommended treatment is effective on daytime symptoms. We aimed to investigate the efficacy of cognitive and behavior therapies for insomnia (CBT-I) on all daytime symptoms explored in the literature using both direct and indirect data. 86 studies (15,578 participants) met inclusion criteria. Results showed significant effects of CBT-I administered face-to-face individually, in group and different self-help settings on depressive symptoms, anxiety, daytime sleepiness, fatigue, quality of life, daytime and social functioning and mental state, with Cohen's d's ranging from -0.52 and 0.81. Our results suggest that CBT-I is effective in the treatment of daytime symptoms, albeit with predominantly small to moderate effects compared to far stronger effects on the core symptoms of insomnia. Effects may be biased for depressive and anxiety symptoms, since many included studies excluded patients with severe levels of these complaints. Further, small to moderate effects may reflect that CBT-I, by improving nighttime symptoms, has a positive effect on daytime symptoms, but it does not target the daytime symptoms directly. Future studies may benefit from adding therapeutic techniques that address daytime symptoms more directly.

Dysfunctional sleep-related cognition and anxiety mediate the relationship between multidimensional perfectionism and insomnia symptoms.

Perfectionism is one of several personality traits associated with insomnia. Whilst research has examined the relationships between perfectionism and insomnia, the mediating role of dysfunctional sleep-related cognition (i.e. sleep-related worry and dysfunctional beliefs about the biological attribution of and consequences of poor sleep) has yet to be examined. This study aimed to determine whether aspects of multidimensional perfectionism were related to increased reporting of insomnia symptoms. In addition, the potential mediating role of dysfunctional sleep-related cognition and anxiety symptoms was examined. Members of the general population (N = 624) completed the Dysfunctional Beliefs and Attitudes About Sleep Scale, the Insomnia Severity Index, the Hospital Anxiety and Depression Scale, and the Multidimensional Perfectionism Scale. The results showed that perfectionism dimensions, anxiety symptoms, and dysfunctional sleep-related cognition were significantly associated with insomnia symptoms. Regression-based mediation analyses further showed that both dysfunctional sleep-related cognition and anxiety significantly mediated the associations between insomnia symptoms and three perfectionism dimensions (i.e. doubts about action, parental expectations, and parental criticism). The experience of perfectionistic tendencies, anxiety, and dysfunctional sleep-related cognition may initiate behavioural strategies (e.g. daytime napping) when faced with an acute sleep problem. However, these strategies may serve to transition insomnia from an acute to a chronic condition.

The European Academy for Cognitive Behavioural Therapy for Insomnia: An initiative of the European Insomnia Network to promote implementation and dissemination of treatment.

Insomnia, the most prevalent sleep disorder worldwide, confers marked risks for both physical and mental health. Furthermore, insomnia is associated with considerable direct and indirect healthcare costs. Recent guidelines in the US and Europe unequivocally conclude that cognitive behavioural therapy for insomnia (CBT-I) should be the first-line treatment for the disorder. Current treatment approaches are in stark contrast to these clear recommendations, not least across Europe, where, if any treatment at all is delivered, hypnotic medication still is the dominant therapeutic modality. To address this situation, a Task Force of the European Sleep Research Society and the European Insomnia Network met in May 2018. The Task Force proposed establishing a European CBT-I Academy that would enable a Europe-wide system of standardized CBT-I training and training centre accreditation. This article summarizes the deliberations of the Task Force concerning definition and ingredients of CBT-I, preconditions for health professionals to teach CBT-I, the way in which CBT-I should be taught, who should be taught CBT-I and to whom CBT-I should be administered. Furthermore, diverse aspects of CBT-I care and delivery were discussed and incorporated into a stepped-care model for insomnia.

Interventions for sleep problems during pregnancy: A systematic review.

Sleep problems during pregnancy are prevalent and could be linked to negative outcomes during pregnancy or post-partum. However, these complaints are often underdiagnosed and undertreated. This review aimed to systematically assess the effectiveness of different interventions to ameliorate poor sleep quality and insomnia during pregnancy. Pubmed, PsycINFO and Medline databases were systematically searched without publication period restriction until 3rd May 2019. Eligible studies had to: include pregnant women of any age and gestational age; use clinical intervention designs targeted at improving sleep outcome; report pre- and post-treatment data for one or more sleep-related outcomes; be published in English, Italian, German, Spanish, or French. Sixteen studies were selected including 1252 expecting mothers. Studies evaluated the efficacy of various interventions: cognitive behavioral interventions for insomnia (4); pharmacotherapy (1); acupuncture (1); mindfulness and yoga (3); relaxation (5) and herbal medication (2). Only six were randomized controlled trials, and only four evaluated longitudinal outcomes. Preliminary support was found for all interventions, but our knowledge is still too limited by lack of evidence. There is an utmost urgency to perform high-quality randomized controlled trials for insomnia interventions during pregnancy and to implement effective programs in standard gynecological care.

Considering Sleep, Mood, and Stress in a Family Context: A Preliminary Study.

BACKGROUND: During the first years of life, parental sleep strongly depends on child's sleep quality. Poor parental sleep may relate to increased stress and negative mood. However, there is a lack of sleep studies focusing on all family members. This study aimed to investigate the relationship between sleep, mood, and stress in mothers, fathers and children. METHODS: Data were obtained from 65 parental couples and 65 children (2 to 36 months). Data on sleep for all family members and stress of parents were completed by both mothers and fathers through questionnaires and sleep diaries. RESULTS: Toddlers' positive mood before nocturnal sleep was significantly associated with reduced wake times after sleep onset. Mothers reported worse sleep quality compared to fathers. Shorter sleep onset latency in fathers and better sleep efficiency in mothers were linked with better self-reported mood upon awakening. In mothers, but not in fathers, poor sleep quality was associated with higher perceived stress. CONCLUSION: Results suggest bidirectional relationships between sleep and mood in children, mothers and fathers. Moreover, results evidence poorer sleep in mothers, compared to fathers, which was linked with increased parenting stress. This gender gap should be further considered in studies with larger samples and in clinical contexts.

Reference Data for Polysomnography-Measured and Subjective Sleep in Healthy Adults.

STUDY OBJECTIVES: Reference data for sleep are needed for the interpretation of clinical sleep parameters. This analysis aimed to provide polysomnography-measured, spectral analytic and subjective reference data based on a sample of healthy adults. In addition, effects of age and sex were investigated. METHODS: The sample was selected from the archival database of the Sleep Center at the University Medical Center Freiburg and consisted of 206 healthy adults aged 19 to 73 years. For an adaptation and a second examination night, polysomnography parameters, spectral analytic data, and subjective sleep estimations are presented. RESULTS: With increasing age, sleep became shorter (less total sleep time, more wake time after sleep onset) and lighter (eg, more percentage of stage N1 sleep, increase in fast activity in the beta range). Sleep in females was deeper than sleep in males (eg, higher percentage of stage N3 sleep). Females had higher overall power density than males. Altogether, it is apparent that sleep parameters exhibit high standard deviations, suggesting a high variability within healthy adults and complicating the specification of reference values. CONCLUSIONS: Our data suggest that the informative value of sleep reference data in healthy individuals is limited because of high interindividual and intraindividual variation within sleep variables. More research, preferably in the form of meta-analyses and/or large international databases, is needed to further investigate the relevance of such reference data for mental and physical health. In the absence of such knowledge, giving patients feedback about deviations from the norm in their sleep profile may give rise to ill-founded concerns and worry.