Sleep and Physiological Dysregulation: A Closer Look at Sleep Intraindividual Variability

Routine, Routine, Routine: Sleep Regularity and its Association with Sleep Metrics in Professional Rugby Union Athletes

BACKGROUND

Maintaining a consistent sleep and wake time is often reported as a key component of circadian rhythmicity and quality sleep. However, the impact of sleep onset and offset time variability on overall sleep outcomes are underreported in elite athlete populations. This study investigated the relationship between sleep onset and offset time variability using the sleep regularity index (SRI) and measures of sleep and well-being in professional rugby union athletes. Twenty-three professional male rugby union athletes (mean ± SD, age: 23 ± 3 y) underwent sleep monitoring via wrist actigraphy for three weeks during a pre-season phase of training and completed a daily wellness questionnaire. Median SRI was calculated and used to stratify the trainees into two quantile groups: >76.4 SRI (Regular, n = 11) and < 76.4 SRI (Irregular, n = 12).

RESULTS

The regular sleep group showed significantly longer total sleep duration (p = 0.02, d = 0.97) compared to the irregular group (7:42 ± 0:29 vs. 7:18 ± 0:20 h: min per night, respectively). Furthermore, while not statistically significant, the regular sleep group showed greater sleep efficiency and less wake episodes compared to irregular sleepers, as demonstrated by moderate effect sizes (d = 0.71 and 0.69, respectively).

CONCLUSIONS

The results from this study indicate that minimizing variability in sleep onset and offset time is beneficial for increasing sleep duration and may improve sleep efficiency during pre-season training in elite male rugby union athletes. This study provides evidence for the importance of including sleep-wake routines as a key component of sleep education interventions.

The impacts of intra-individual daily sleep variability on daytime functioning and sleep architecture in healthy young adults: An experimental study

Sleep variability is commonly seen in the young populations. This study aimed to examine the impacts of experimentally induced sleep variability on sleepiness, mood, cognitive performance and sleep architectures among young adults. Thirty-six healthy individuals (aged 18-22 years) were randomly assigned to either variable sleep schedule (n = 20) or control (n = 16) groups. The protocol involved 1 week of regular sleep (time in bed = 7.5 hr) in the home setting, followed by one adaptation night (time in bed = 7.5 hr), one baseline night (time in bed = 7.5 hr), and 6 nights of sleep manipulation in the laboratory monitored by polysomnography (three cycles of variable sleep schedule by changing daily time in bed alternating between 6 hr and 9 hr for variable sleep schedule group versus fixed sleep schedule with daily time in bed for 7.5 hr for control group). Sleepiness, mood, sustained attention, processing speed, response inhibition and working memory were measured every morning and evening. The variable sleep schedule group reported a higher level of sleepiness, especially in the mornings, and increased negative mood in the evenings. There were no significant differences in positive mood, cognitive performance and sleep macro- and micro-structures. Our results showed the negative effects of sleep variability on daytime functioning especially sleepiness and negative mood, suggesting the need to address variable sleep schedules through sleep intervention.

Relationship of sleep with diurnal cortisol rhythm considering sleep measurement and cortisol sampling schemes

Information on the relationships between the previous night's sleep and the next-day diurnal cortisol rhythm is inconsistent due to confounding factors such as sleep measurements (trait/state sleep and objective/subjective sleep) and cortisol sampling schemes. Therefore, this study aimed to investigate these relationships, considering the confounding factors. College students (n = 79) wore actigraphy for 3 days to undergo an evaluation of previous night-time sleep objectively and reported their subjective sleep parameters in a sleep diary. In addition, participants provided six salivary cortisol samples daily. Furthermore, six cortisol sampling schemes were created to reflect diurnal cortisol rhythms, and two different methods were used to calculate the index of diurnal cortisol slope (DCS). A multilevel model was created to examine the impact of both trait and state sleep on next-day diurnal cortisol rhythm. The results revealed that higher objective state sleep efficiency and longer objective state total sleep time were associated with a higher cortisol awakening response (CAR). Moreover, higher objective trait sleep efficiency and longer objective trait total sleep time were associated with higher waking cortisol levels and steeper DCS. In addition, a minimum of four saliva samples were required at different time points, including upon waking, 30 min after waking, 1 h after waking, and at bedtime, to explore the relationship of sleep efficiency/total sleep time with waking cortisol, CAR, and DCS. Furthermore, the index of the peak-to-bed slope was appropriately employed to examine the relationship between sleep efficiency and DCS, whereas the wake-to-bed slope was effective for examining the relationship between total sleep time and DCS. In summary, this study clarified the relationship between sleep and next-day diurnal cortisol rhythm and suggested a cost-effective cortisol sampling schedule and calculation methods.

The importance of sleep regularity: a consensus statement of the National Sleep Foundation sleep timing and variability panel

OBJECTIVE

To develop and present consensus findings of the National Sleep Foundation sleep timing and variability panel regarding the impact of sleep timing variability on health and performance.

METHODS

The National Sleep Foundation assembled a panel of sleep and circadian experts to evaluate the scientific evidence and conduct a formal consensus and voting procedure. A systematic literature review was conducted using the NIH National Library of Medicine PubMed database, and panelists voted on the appropriateness of 3 questions using a modified Delphi RAND/UCLA Appropriateness Method with 2 rounds of voting.

RESULTS

The literature search and panel review identified 63 full text publications to inform consensus voting. Panelists achieved consensus on each question: (1) is daily regularity in sleep timing important for (a) health or (b) performance? and (2) when sleep is of insufficient duration during the week (or work days), is catch-up sleep on weekends (or non-work days) important for health? Based on the evidence currently available, panelists agreed to an affirmative response to all 3 questions.

CONCLUSIONS

Consistency of sleep onset and offset timing is important for health, safety, and performance. Nonetheless, when insufficient sleep is obtained during the week/work days, weekend/non-work day catch-up sleep may be beneficial.

Stronger Associations Between Sleep and Mental Health in Adults with Autism: A UK Biobank Study

This study examined sleep and its cognitive and affective correlates in adults with and without autism spectrum disorder (ASD), utilizing UK Biobank data. There were no group differences in subjective sleep duration [n = 220 ASD; n = 2200 general population (GP)]. Accelerometer measures of sleep duration or nighttime activity did not differ by group, but sleep efficiency was marginally lower in ASD (n = 83 ASD; n = 824 GP). Sleep efficiency was associated with wellbeing and mental health, and pathways between accelerometer sleep measures and wellbeing and mental health were significantly stronger for adults with ASD (who also reported substantially poorer wellbeing and > 5 × likelihood of experiencing mental distress). These findings highlight the need to monitor sleep to maintain good mental health in adult ASD.

Physical Activity and Cortisol Regulation: A Meta-Analysis

Physical activity participation is associated with effective stress coping, indicated by decreases in both physiological stress reactivity and perceived stress. Quantifying the effect of physical activity on the diurnal regulation of one key physiological stress indicator, the stress hormone, cortisol, across studies may demonstrate the extent to which physical activity participation is associated with diurnal HPA axis regulation. We meta-analyzed studies examining relations between physical activity participation and indices of HPA axis regulation: the diurnal cortisol slope and the cortisol awakening response. We also examined moderators of the relation. The analysis revealed a small, non-zero negative averaged correlation between physical activity and the diurnal cortisol slope (r = -0.043, 95% CI [-0.080, -0.004]). Examination of sample sociodemographic differences, study design characteristics, cortisol measurement methods, and physical activity variables as moderators revealed few effects on the relation between physical activity and diurnal cortisol slope. We did not observe lower levels of variability in the mean cortisol awakening response at higher levels of physical activity participation, and moderator analyses showed little evidence of reductions in heterogeneity for this effect. We found some evidence of systematic publication bias. Findings suggest higher physical activity is associated with a steeper diurnal cortisol slope. However, the cortisol awakening response did not differ by physical activity level. Future studies testing the physical activity and cortisol regulation association should use standardized physical activity measures, follow guidelines for better quality cortisol sampling collection and analysis, and test relations in large-scale empirical studies to confirm the direction and causality of the effect.

Investigating sleep, stress, and mood dynamics via temporal network analysis

OBJECTIVE/BACKGROUND

Prior research has emphasized the bidirectional relationships between sleep, stress, and affective states, such as depression. Given the inherent variability and fluctuations associated with sleep, assessing how sleep and affective variables function within a dynamic system may help further uncover possible causes and consequences of sleep disturbances, as well as find candidate targets for intervention. To this end, we examined dynamic relationships between self-reported stress, depressed mood, and clinically-relevant sleep parameters via temporal network analysis.

METHODS

Participants were 401 nurses (92% female, 78% White, Mage = 39.47 years) who completed 14 days of sleep diaries incorporating self-reported stress and depression, as well as total sleep time, sleep efficiency, sleep onset latency, and wake after sleep onset.

RESULTS AND CONCLUSIONS

Overall, total sleep time emerged as a highly influential variable in the context of "outstrength centrality," meaning total sleep time had numerous outward connections with other variables (e.g., stress and sleep efficiency). The high outstrength centrality of total sleep time suggests this variable is a source of activation within this dynamic system. Conversely, stress showed high "instrength centrality," suggesting this variable was highly impacted by other variables in the system, such as depressed mood and sleep efficiency. These findings emphasize the importance of assessing unfolding sleep processes within a naturalistic setting, and implicate the role of total sleep time in fueling depressed mood and stress. Discussion emphasizes implications of these results for understanding the connections between sleep, stress, and depression as well as clinical relevance of these findings.

Separating the influences of means and daily variations of sleep on the stress-induced salivary cortisol response

BACKGROUND

Previous research regarding the effects of sleep quality and quantity on the acute stress response has yielded inconsistent findings. This may be attributed to various factors, including composite sleep components (i.e., means and daily variations) and mixed cortisol stress response (i.e., reactivity and recovery). Thus, this study aimed to separate the effects of means and daily variations of sleep on the reactivity and recovery of cortisol responses to psychological challenges.

METHODS

In study 1, we recruited 41 healthy participants (24 women; age range, 18-23 years), monitored their sleep during seven consecutive days via wrist actigraphy and sleep diaries, and adopted the Trier Social Stress Test (TSST) paradigm to induce acute stress. Study 2 consisted of a validation experiment using the ScanSTRESS paradigm, which included 77 additional healthy individuals (35 women; age range, 18-26 years). Similarly to the TSST, the ScanSTRESS induces acute stress using uncontrollability and social evaluation. In both studies, saliva samples from the participants were collected before, during, and after the acute stress task.

RESULTS

Using residual dynamic structural equation modeling, both study 1 and study 2 demonstrated that higher means of objective sleep efficiency, and longer means of objective sleep duration were related to greater cortisol recovery. In addition, fewer daily variations in objective sleep duration were associated with greater cortisol recovery. However, there was no correlation between sleep variables and cortisol reactivity, except for the daily variations in objective sleep duration in study 2. No correlation was observed between subjective sleep and cortisol response to stress.

CONCLUSIONS

The present study separated two features of multi-day sleep patterns and two components of cortisol stress response, providing a more comprehensive picture of the effect of sleep on the stress-induced salivary cortisol response, and contributing to the future development of targeted interventions for stress-related disorders.

Sleep-Opt-In: A Randomized Controlled Pilot Study to Improve Sleep and Glycemic Variability in Adults With Type 1 Diabetes

PURPOSE

The purpose of this study was to evaluate the feasibility and acceptability of a technology-assisted behavioral sleep intervention (Sleep-Opt-In) and to examine the effects of Sleep-Opt-In on sleep duration and regularity, glucose indices, and patient-reported outcomes. Short sleep duration and irregular sleep schedules are associated with reduced glycemic control and greater glycemic variability.

METHODS

A randomized controlled parallel-arm pilot study was employed. Adults with type 1 diabetes (n = 14) were recruited from the Midwest and randomized 3:2 to the sleep-optimization (Sleep-Opt-In) or Healthy Living attention control group. Sleep-Opt-In was an 8-week, remotely delivered intervention consisting of digital lessons, sleep tracker, and weekly coaching phone calls by a trained sleep coach. Assessments of sleep (actigraphy), glucose (A1C, continuous glucose monitoring), and patient-reported outcomes (questionnaires for daytime sleepiness, fatigue, diabetes distress, and depressive mood) were completed at baseline and at completion of the intervention.

RESULTS

Sleep-Opt-In was feasible and acceptable. Those in Sleep-Opt-In with objectively confirmed short or irregular sleep demonstrated an improvement in sleep regularity (25 minutes), reduced glycemic variability (3.2%), and improved time in range (6.9%) compared to the Healthy Living attention control group. Patient-reported outcomes improved only for the Sleep-Opt-In group. Fatigue and depressive mood improved compared to the control.

CONCLUSIONS

Sleep-Opt-In is feasible, acceptable, and promising for further evaluation as a means to improve sleep duration or regularity in the population of people with type 1 diabetes.

Irregular sleep and cardiometabolic risk: Clinical evidence and mechanisms

Sleep regularity is an essential part of the multidimensional sleep health framework. The phenomenon of irregular sleep patterns is widespread in contemporary lifestyles. This review synthesizes clinical evidence to summarize the measures of sleep regularity and discusses the role of different sleep regularity indicators in developing cardiometabolic diseases (coronary heart disease, hypertension, obesity, and diabetes). Existing literature has proposed several measurements to assess sleep regularity, mainly including the standard deviation (SD) of sleep duration and timing, sleep regularity index (SRI), interdaily stability (IS), and social jetlag (SJL). Evidence on associations between sleep variability and cardiometabolic diseases varies depending on the measure used to characterize variability in sleep. Current studies have identified a robust association between SRI and cardiometabolic diseases. In comparison, the association between other metrics of sleep regularity and cardiometabolic diseases was mixed. Meanwhile, the associations of sleep variability with cardiometabolic diseases differ across the population. SD of sleep characteristics or IS may be more consistently associated with HbA1c in patients with diabetes compared with the general population. The association between SJL and hypertension for patients with diabetes was more accordant than in the general population. Interestingly, the age-stratified association between SJL and metabolic factors was observed in the present studies. Furthermore, the relevant literature was reviewed to generalize the potential mechanisms through which irregular sleep increases cardiometabolic risk, including circadian dysfunction, inflammation, autonomic dysfunction, hypothalamic-pituitary-adrenal (HPA) axis disorder, and gut dysbiosis. Health-related practitioners should give more attention to the role of sleep regularity on human cardiometabolic in the future.

Racial/ethnic variations in inflammatory markers: exploring the role of sleep duration and sleep efficiency

Individuals from minoritized racial/ethnic groups have higher levels of circulating inflammatory markers. However, the mechanisms underlying these differences remain understudied. The objective of this study was to examine racial/ethnic variations in multiple markers of inflammation and whether impaired sleep contributes to these racial/ethnic differences. Nurses from two regional hospitals in Texas (n = 377; 71.62% White; 6.90% Black; 11.14% Hispanic, 10.34% Asian; mean age = 39.46; 91.78% female) completed seven days of sleep diaries and actigraphy to assess mean and variability in total sleep time (TST) and sleep efficiency (SE). On day 7, blood was drawn to assess 4 inflammatory markers: C-reactive protein (CRP), Interleukin-6 (IL-6), Interleukin-1 beta (IL-1β), and tumor necrosis factor-alpha (TNF-α). Results from regression models showed differences in inflammatory markers by race/ethnicity, adjusting for age and gender. The associations between sleep parameters and inflammatory markers also varied by race/ethnicity. Among White nurses, lower mean and greater variability in actigraphy-determined TST and greater variability in diary-determined TST were associated with higher levels of IL-6. Among Black nurses, lower mean diary-determined SE was associated with higher levels of IL-6 and IL-1β. Among Hispanic nurses, greater diary-determined mean TST was associated with higher CRP. Among Asian nurses, greater intraindividual variability in actigraphy-determined SE was associated with lower CRP. Among nurses, we did not find racial/ethnic disparities in levels of inflammation. However, analyses revealed differential relationships between sleep and inflammatory markers by race/ethnicity. Results highlight the importance of using a within-group approach to understand predictors of inflammatory markers.

A preliminary investigation of the role of intraindividual sleep variability in substance use treatment outcomes

INTRODUCTION

Poor sleep health is common among individuals in early treatment for substance use disorders (SUDs) and may serve an important role in predicting SUD outcomes. However, sleep parameters have been inconsistently linked with risk of relapse, perhaps because previous research has focused on mean values of sleep parameters (e.g., total sleep time [TST], sleep efficiency [SE], and sleep midpoint [SM]) across multiple nights rather than night-to-night fluctuations (i.e., intraindividual variability [IIV]). The current study assessed sleep across the first week of SUD treatment, with the aim of prospectively examining the relationship between mean and IIV of TST, SE, and SM and treatment completion and relapse within one-month post-treatment.

METHODS

Treatment-seeking adults (N = 23, M_age = 40.1, 39% female) wore an actigraph to assess sleep for one week at the beginning of an intensive outpatient program treatment. Electronic medical record and follow-up interviews were utilized to determine treatment outcomes.

RESULTS

Greater IIV in TST was associated with higher odds of relapse (OR = 3.55, p =.028). Greater IIV in SM was associated with lower odds of treatment completion, but only when removing mean SM from the model (OR = 0.75, p =.046).

DISCUSSION

Night-to-night variability in actigraphy-measured TST is more strongly associated with SUD treatment outcomes than average sleep patterns across the week. Integrating circadian regulation into treatment efforts to improve SUD treatment outcomes may be warranted. Given the small sample size utilized in the present study, replication of these analyses with a larger sample is warranted.

Sleep irregularity and nonsuicidal self-injurious urges and behaviors

STUDY OBJECTIVES

The objectives of this study were to examine the relationships between sleep regularity and nonsuicidal self-injury (NSSI), including lifetime NSSI history and daily NSSI urges.

METHODS

Undergraduate students (N = 119; 18-26 years), approximately half of whom endorsed a lifetime history of repetitive NSSI, completed a 10-day actigraphy and ecological momentary assessment (EMA) protocol. A Sleep Regularity Index was calculated for all participants using scored epoch by epoch data to capture rapid changes in sleep schedules. Participants responded to EMA prompts assessing NSSI urge severity and negative affect three times daily over the 10-day assessment period.

RESULTS

Results indicate that individuals with a repetitive NSSI history were more likely to experience sleep irregularity than those without a history of NSSI. Findings also suggest that sleep irregularity was associated with more intense urges to engage in NSSI on a daily basis, even after accounting for average daily sleep duration, sleep timing, negative affect, and NSSI history. Neither sleep duration nor sleep timing was associated with NSSI history nor daily NSSI urge intensity.

CONCLUSIONS

Findings suggest that sleep irregularity is linked with NSSI, including NSSI history and intensity of urges to engage in NSSI. The present study not only supports the growing evidence linking sleep disturbance with the risk for self-injury but also demonstrates this relationship using actigraphy and real-time assessments of NSSI urge severity. Findings highlight the importance of delineating the nuances in sleep irregularity that are proximally associated with NSSI risk and identifying targets for intervention.

Sleep Deficiency in Young Children

There is growing public health concern about the high prevalence of sleep deficiency in early childhood and the associated risk for sleep-associated poor health outcomes, including metabolic, cardiovascular, and mental health. The recent shift to conceptualize sleep health as a multidimensional construct, influenced by socioecological factors, highlights the potential role of sleep in health disparities. Understanding the development of sleep health and the emergence of sleep disorders in early life is a current priority in pediatric sleep research. Future behavioral sleep interventions should consider the multiple socioecological influences on children's sleep health and be tested using inclusive sampling methods.

The Effects of Objective Push-type Sleep Feedback on Habitual Sleep Behavior and Momentary Symptoms in Daily Life: Mobile Health Intervention Trial using a Healthcare IoT System (Preprint)

Background

Sleep is beneficial for physical and mental health. Several mobile and wearable sleep-tracking devices have been developed, and personalized sleep feedback is the most common functionality among these devices. To date, no study has implemented an objective push-type feedback message and investigated the characteristics of habitual sleep behavior and diurnal symptoms when receiving sleep feedback.

Objective

We conducted a mobile health intervention trial to examine whether sending objective push-type sleep feedback changes the self-reported mood, physical symptoms, and sleep behavior of Japanese office workers.

Methods

In total, 31 office workers (mean age 42.3, SD 7.9 years; male-to-female ratio 21:10) participated in a 2-arm intervention trial from November 30 to December 19, 2020. The participants were instructed to indicate their momentary mood and physical symptoms (depressive mood, anxiety, stress, sleepiness, fatigue, and neck and shoulder stiffness) 5 times a day using a smartphone app. In addition, daily work performance was rated once a day after work. They were randomly assigned to either a feedback or control group, wherein they did or did not receive messages about their sleep status on the app every morning, respectively. All participants wore activity monitors on their nondominant wrists, through which objective sleep data were registered on the web on a server. On the basis of the estimated sleep data on the server, personalized sleep feedback messages were generated and sent to the participants in the feedback group using the app. These processes were fully automated.

Results

Using hierarchical statistical models, we examined the differences in the statistical properties of sleep variables (sleep duration and midpoint of sleep) and daily work performance over the trial period. Group differences in the diurnal slopes for mood and physical symptoms were examined using a linear mixed effect model. We found a significant group difference among within-individual residuals at the midpoint of sleep (expected a posteriori for the difference: −15, 95% credible interval −26 to −4 min), suggesting more stable sleep timing in the feedback group. However, there were no significant group differences in daily work performance. We also found significant group differences in the diurnal slopes for sleepiness (P<.001), fatigue (P=.002), and neck and shoulder stiffness (P<.001), which was largely due to better scores in the feedback group at wake-up time relative to those in the control group.

Conclusions

This is the first mobile health study to demonstrate that objective push-type sleep feedback improves sleep timing of and physical symptoms in healthy office workers. Future research should incorporate specific behavioral instructions intended to improve sleep habits and examine the effectiveness of these instructions.

Sleep onset, duration, or regularity: which matters most for child adiposity outcomes?

BACKGROUND/OBJECTIVES

Sleep measures, such as duration and onset timing, are associated with adiposity outcomes among children. Recent research among adults has considered variability in sleep and wake onset times, with the Sleep Regularity Index (SRI) as a comprehensive metric to measure shifts in sleep and wake onset times between days. However, little research has examined regularity and adiposity outcomes among children. This study examined the associations of three sleep measures (i.e., sleep duration, sleep onset time, and SRI) with three measures of adiposity (i.e., body mass index [BMI], waist circumference, and waist-to-height ratio [WHtR]) in a pediatric sample.

SUBJECTS/METHODS

Children (ages 4-13 years) who were part of the U.S. Newborn Epigenetic STudy (NEST) participated. Children (N = 144) wore an ActiGraph for 1 week. Sleep measures were estimated from actigraphy data. Weight, height, and waist circumference were measured by trained researchers. BMI and WHtR was calculated with the objectively measured waist and height values. Multiple linear regression models examined associations between child sleep and adiposity outcomes, controlling for race/ethnicity, child sex, age, mothers' BMI and sleep duration.

RESULTS

When considering sleep onset timing and duration, along with demographic covariates, sleep onset timing was not significantly associated with any of the three adiposity measures, but a longer duration was significantly associated with a lower BMI Z-score (β = -0.29, p < 0.001), waist circumference (β = -0.31, p < 0.001), and WHtR (β = -0.38, p < 0.001). When considering SRI and duration, duration remained significantly associated with the adiposity measures. The SRI and adiposity associations were in the expected direction, but were non-significant, except the SRI and WHtR association (β = -0.16, p = 0.077) was marginally non-significant.

CONCLUSIONS

Sleep duration was consistently associated with adiposity measures in children 4-13 years of age. Pediatric sleep interventions should focus first on elongating nighttime sleep duration, and examine if this improves child adiposity outcomes.

Adolescents' sleep and adjustment: Reciprocal effects

Reciprocal relations between sleep and adjustment were investigated. Participants included 246 adolescents (M = 15.80 years; 67.5% White, 32.5% Black/African American; 53% female, 47% male) at Time 1 (data collected 2012-2013), 227 at Time 2 (M = 16.78 years) and 215 at Time 3 (M = 17.70 years). Sleep-wake variables were measured with self-reports (sleepiness) and actigraphy (average sleep minutes and efficiency, variability in sleep minutes and efficiency). Adolescents reported on depression and anxiety symptoms, and parents reported on externalizing problems. Greater variability in sleep duration and efficiency as well as sleepiness predicted adjustment problems (range of R² : 36%-60%). Reciprocal relations were supported mostly for sleepiness (range of R² : 16%-32%). Results help understand bidirectional relations between sleep and adjustment.

Greater variability in daily sleep efficiency predicts depression and anxiety in young adults: Estimation of depression severity using the two-week sleep quality records of wearable devices

OBJECTIVES

Sleep disturbances are associated with both the onset and progression of depressive disorders. It is important to capture day-to-day variability in sleep patterns; irregular sleep is associated with depressive symptoms. We used sleep efficiency, measured with wearable devices, as an objective indicator of daily sleep variability.

MATERIALS AND METHODS

The total sample consists of 100 undergraduate and graduate students, 60% of whom were female. All were divided into three groups (with major depressive disorder, mild depressive symptoms, and controls). Self-report questionnaires were completed at the beginning of the experiment, and sleep efficiency data were collected daily for 2 weeks using wearable devices. We explored whether the mean value of sleep efficiency, and its variability, predicted the severity of depression using dynamic structural equation modeling.

RESULTS

More marked daily variability in sleep efficiency significantly predicted levels of depression and anxiety, as did the average person-level covariates (longer time in bed, poorer quality of life, lower extraversion, and higher neuroticism).

CONCLUSION

Large swings in day-to-day sleep efficiency and certain clinical characteristics might be associated with depression severity in young adults.

Longitudinal associations between adolescents' sleep and adjustment: Respiratory sinus arrhythmia as a moderator

Sleep and autonomic nervous system functioning are important bioregulatory systems. Poor sleep and low baseline respiratory sinus arrhythmia (RSA), a measure of parasympathetic nervous system activity, are associated with externalizing behaviors and depressive symptoms in youth. Rarely, however, have measures of these systems been examined conjointly. The present study examined baseline RSA (RSA-B) as a moderator of longitudinal relations between adolescent sleep and adjustment. Participants were 256 adolescents (52% girls, 66% White/European American, 34% Black/African American) from small towns and surrounding rural communities in the southeastern United States. Sleep (minutes, efficiency, variability in minutes and efficiency) was assessed at age 15 via actigraphs across seven nights. RSA-B was derived from electrocardiogram data collected at rest. Adolescents self-reported externalizing problems and depressive symptoms at ages 15 and 17. Controlling for age 15 adjustment, findings generally demonstrated that sleep predicted age 17 adjustment particularly at higher (rather than lower) levels of RSA-B, such that adolescents with good sleep (more minutes and lower variability) and high RSA-B were at lowest risk for maladjustment. The results highlight the value of examining multiple bioregulatory processes conjointly and suggest that promoting good sleep habits and regulation of physiological arousal should support adolescent adjustment.

Prenatal insomnia and childbirth-related PTSD symptoms: A prospective population-based cohort study

BACKGROUND

Certain populations are at high risk of experiencing a traumatic event and developing post-traumatic stress disorder (PTSD). Yet, primary preventive interventions against PTSD are lacking. It is therefore crucial to identify pre-traumatic risk factors, which could be targeted with such interventions. Insomnia may be a good candidate, but studies on civilians are sparse. Furthermore, the mechanisms at stake in the relationship between pre-traumatic insomnia and PTSD symptoms are unclear.

METHODS

This prospective population-based cohort study (n = 1,610) examined the relationship between insomnia symptoms at 32 weeks of pregnancy and childbirth-related PTSD (CB-PTSD) symptoms at eight weeks postpartum. Postnatal insomnia symptoms, prenatal psychological symptoms (depression, anxiety, PTSD, fear of childbirth), subjective birth experience (SBE) and birth medical severity were included as covariates in the analyses, which were based on a Piecewise Structural Equation Modelling approach.

RESULTS

The relationship between prenatal insomnia and CB-PTSD symptoms was mediated by negative SBE and postnatal insomnia symptoms. All relationships involving insomnia symptoms had small or very small effect sizes.

LIMITATIONS

This study used self-report questionnaires. Postnatal insomnia and CB-PTSD symptoms were concurrently measured.

CONCLUSION

Prenatal insomnia symptoms may impair the ability to cope with a difficult birth experience and contribute to postnatal insomnia, a risk factor for CB-PTSD. Thus, prenatal insomnia symptoms may be a promising target for CB-PTSD primary preventive interventions, although other prenatal psychological symptoms could also be considered. Even beyond the perinatal context, future studies on pre-traumatic insomnia and PTSD should include post-traumatic insomnia as a covariate.

Allostatic Load and Its Impact on Health: A Systematic Review

INTRODUCTION

Allostatic load refers to the cumulative burden of chronic stress and life events. It involves the interaction of different physiological systems at varying degrees of activity. When environmental challenges exceed the individual ability to cope, then allostatic overload ensues. Allostatic load is identified by the use of biomarkers and clinical criteria.

OBJECTIVE

To summarize the current knowledge on allostatic load and overload and its clinical implications based on a systematic review of the literature.

METHODS

PubMed, PsycINFO, Web of Science, and the Cochrane Library were searched from inception to December 2019. A manual search of the literature was also performed, and reference lists of the retrieved articles were examined.We considered only studies in which allostatic load or overload were adequately described and assessed in either clinical or non-clinical adult populations.

RESULTS

A total of 267 original investigations were included. They encompassed general population studies, as well as clinical studies on consequences of allostatic load/overload on both physical and mental health across a variety of settings.

CONCLUSIONS

The findings indicate that allostatic load and overload are associated with poorer health outcomes. Assessment of allostatic load provides support to the understanding of psychosocial determinants of health and lifestyle medicine. An integrated approach that includes both biological markers and clinimetric criteria is recommended.

Do self-ratings of the Pittsburgh Sleep Quality Index reflect actigraphy recordings of sleep quality or variability? An exploratory study of bipolar disorders versus healthy controls

Sleep disturbances are typical symptoms of acute episodes of bipolar disorder (BD) and differentiate euthymic BD cases from healthy controls (HC). Researchers often employ objective recordings to evaluate sleep patterns, such as actigraphy, whilst clinicians often use subjective ratings, such as the Pittsburgh Sleep Quality Index (PSQI). As evidence suggests the measures may disagree, we decided to compare subjective (PSQI) and objective (3 weeks of actigraphy) sleep profiles in BD cases and HC (n = 154). We examined whether a dimensional approach helps to illustrate different patterns of sleep disturbances and whether the concordance between subjective and objective recordings varies according to clinical status (BD versus HC). Principal component analysis (PCA) extracted two factors from the PSQI, and separate PCAs of actigraphy recordings extracted two factors for mean values of sleep parameters and one factor for intra-individual variability. Correlational and linear regression analyses of PCA-derived dimensions demonstrated that, in both BD and HC, a PSQI "Sleep duration-efficiency" factor was significantly correlated with an actigraphy "Sleep initiation-duration" factor. Furthermore, in BD cases only, the PSQI total score and a PSQI "Sleep Impairments" factor were each significantly correlated with an actigraphy "Sleep Variability" factor. Overall, we found that subjective experiences of sleep may be modulated by different components of objectively recorded sleep in BD compared with HC. Also, the use of PCA enabled us to consider the multi-dimensional nature of subjective sleep, whilst the inclusion of intra-individual sleep variability afforded a more subtle evaluation of objective sleep.

Outcomes of the Transdiagnostic Intervention for Sleep and Circadian Dysfunction (TranS-C) in a community setting: Unpacking comorbidity

OBJECTIVE

Comorbidity and subdiagnostic symptoms are understudied for sleep and circadian problems. We evaluated 1) impairment associated with (a) number of sleep and circadian problems and (b) diagnostic threshold (full diagnosis vs. subdiagnostic symptoms), and 2) Transdiagnostic Sleep and Circadian Intervention (TranS-C) outcomes for participants with specific sleep and circadian problems.

METHOD

Community participants (N = 121) with serious mental illness and sleep and circadian problem(s) were randomized to receive TranS-C plus usual care (TranS-C + UC) or usual care plus delayed TranS-C (UC-DT). Overall impairment, psychiatric symptoms, and sleep and circadian dysfunction were assessed at pre-treatment, post-treatment, and 6-month follow-up.

RESULTS

Higher numbers of sleep and circadian problems, versus one problem, were associated with worse overall impairment, psychiatric symptoms, and sleep and circadian dysfunction (ps < 0.05, ω2 = 0.06-0.15). Diagnostic threshold was not associated with baseline functioning (ps > 0.05). TranS-C + UC versus UC-DT was associated with psychosocial and sleep and circadian improvements for specific sleep and circadian problems (insomnia, hypersomnia, parasomnias, periodic limb movement/restless leg syndrome, circadian rhythm disorders), though improvements varied by problem. TranS-C + UC outcomes were not moderated by number of sleep and circadian problems (ps > 0.05).

CONCLUSION

Higher numbers of sleep and circadian problems, not diagnostic threshold, were associated with greater impairment. Transdiagnostic utility of TranS-C + UC was supported.

Discrimination and adjustment in adolescence: The moderating role of sleep

STUDY OBJECTIVES

We examined multiple actigraphy-based sleep parameters as moderators of associations between experiences of general and racial discrimination and adolescent internalizing symptoms (anxiety, depression) and externalizing behavior (rule-breaking). Adolescent sex and race were examined as additional moderators.

METHODS

Participants were 272 adolescents (Mage = 17.3 years, SD = 0.76; 51% male; 59% White/European American, 41% Black/African American). Sleep was assessed using actigraphs for 7 consecutive nights from which sleep duration (minutes), efficiency, and variability in minutes over the week were derived. Youth reported on their experiences of general discrimination, racial discrimination, anxiety, depressive symptoms, and rule-breaking behavior.

RESULTS

Both types of discrimination were associated with poorer adjustment outcomes. Longer sleep duration, greater sleep efficiency, and less variability in sleep duration were protective in associations between race-specific and general discrimination and internalizing symptoms. Findings for duration and efficiency were more pronounced for females such that the adverse effects of discrimination were minimized among females with longer and more efficient sleep. Greater variability in sleep exacerbated rule-breaking behavior among adolescents experiencing general or racial discrimination. Associations did not differ by adolescent race.

CONCLUSIONS

Short and poor-quality sleep may exacerbate internalizing symptoms for adolescents experiencing discrimination, particularly females. Variability in sleep duration was a key moderator of associations between discrimination and internalizing symptoms as well as rule-breaking behavior. Findings illustrate that actigraphy-assessed sleep parameters play a key role in ameliorating or exacerbating adjustment problems associated with discrimination.

Association between health behaviours and cardiometabolic dysregulation: a population-based survey among healthy adults in Hong Kong

OBJECTIVE

To explore the association between cardiometabolic dysregulation, an integral component of allostatic load, and health risk behaviours (HRBs) of the Hong Kong healthy adult population.

DESIGN

Secondary analysis of cross-sectional anonymous data.

SETTING

Data on sociodemographics, self-reported health status, HRBs and biomarkers were extracted from the Hong Kong Population Health Survey 2014/2015.

PARTICIPANTS

One thousand five hundred and fifty-one participants aged 18-64 years without self-reported diagnoses of hypertension, diabetes mellitus, hyperlipidaemia, cardiovascular disease, cognitive impairment or cancer.

PRIMARY OUTCOME MEASURES

Cardiometabolic dysregulation index (CMDI), ranging from 0 to 6, was calculated by counting the number of biomarkers including systolic blood pressure, diastolic blood pressure, waist to hip ratio, glycated haemoglobin, total cholesterol to high-density lipoprotein cholesterol ratio, and triglycerides that were above the respective normal level suggested by international guidelines and literature. HRBs including smoking, dietary habits and sleeping hours were collected by self-report questionnaire. Alcohol consumption was assessed by the 10-item Alcohol Use Disorders Identification Test, while physical activity level was measured using the Global Physical Activity Questionnaire. A composite HRB score, ranging from 0 to 5, was calculated as the cumulative number of HRBs. The effect of HRB on CMDI was evaluated by negative binomial regression with adjustment for socioeconomic status, health awareness and comorbidities of the participants.

RESULTS

The mean CMDI of the studied population was 1.6; 29.5% had a CMDI of 0, whereas 1.5% had a CMDI of 6. Significant difference was observed in mean CMDI between gender and different age groups. Sleeping less than 6 hours (incidence rate ratio (IRR)=1.26, p<0.001), smoking (IRR=1.15, p=0.027), insufficient physical activity (IRR=1.12, p=0.007) and higher composite HRB score (IRR=1.12, 95% CI 1.06 to 1.18) were significantly associated with higher CMDI.

CONCLUSION

Smoking, physical inactivity and inadequate sleep-an essential yet often overlooked health behaviour-were associated with higher CMDI in the Hong Kong healthy adult population.

[Secondary Data Analysis on the Factors Influencing Premenstrual Symptoms of Shift Work Nurses: Focused on the Sleep and Occupational Stress]

PURPOSE

This study aimed to examine premenstrual symptoms (PMS) of shift nurses and identify the association between PMS, sleep, and occupational stress.

METHODS

This study was conducted with a secondary data analysis that used data from the Shift Work Nurse's Health and Turnover study. The participants were 258 nurses who were working in shifts including night shifts. PMS, sleep patterns (sleep time and sleep time variability), sleep quality, and the occupational stress of each participant were measured using the Moos Menstrual Distress Questionnaire, a sleep diary, an actigraph, the Insomnia Severity Index, and the Korean Occupational Stress Scale, respectively. Data were analyzed using SPSS 23 and STATA 15.1 to obtain descriptive statistics, Pearson's correlation coefficients, multiple linear regression with generalized estimating equations (GEE) and Baron and Kenny's mediating analysis.

RESULTS

The average PMS score, average sleep time, average sleep time variability, average sleep quality score, and average occupational stress score of the participants was 53.95 ± 40.45, 7.52 ± 0.89 hours, 32.84 ± 8.43%, 12.34 ± 5.95, and 49.89 ± 8.98, respectively. A multiple linear regression analysis with GEE indicated that sleep time variability (B = 0.86, p = .001), and sleep quality (B = 2.36, p < .001) had negative effects on nurses' PMS. We also found that sleep quality had a complete mediating effect in the relationship between occupational stress and PMS.

CONCLUSION

These findings indicate that both sleep time variability and sleep quality are important factors associated with PMS among shift work nurses. To improve shift nurses' PMS status, strategies are urgently needed to decrease sleep time variability and increase sleep quality.

The Sleep Regularity Questionnaire: development and initial validation

BACKGROUND/OBJECTIVE

Sleep is a critically important behavior which influences diverse aspects of health, functioning, and longevity. An increasing literature suggests the importance of sleep regularity, also referred to as sleep inconsistency, sleep variability, or intraindividual variability in sleep. Given there is no brief, subjective measure of sleep regularity, the purpose of this study was to develop the Sleep Regularity Questionnaire (SRQ) and to begin the process of examining its psychometric properties using a construct-validation approach.

PARTICIPANTS/METHODS

In an online study of sleep and health, participants (n = 3249; M_age (SD) = 42.77 (16.73); 48.5% female; 77.3% white) completed the in-development SRQ, as well as the Insomnia Severity Index and the Pittsburgh Sleep Quality Index.

RESULTS

An exploratory factor analysis followed by a confirmatory factor analysis revealed a two factor structure, represented by circadian regularity and sleep continuity regularity, with good model fit indices (X² = 50.9, df = 7, p < 0.001; RMSEA = 0.06; CFI = 0.99; NFI = 0.99; IFI = 0.99; TLI = 0.98). Test-retest reliability, as well as concurrent, convergent and incremental validity were examined, with promising results.

CONCLUSIONS

Preliminary psychometrics suggest that the SRQ is a valid and stable instrument for the assessment of sleep regularity in adults that is related to, but distinct from, other established sleep constructs. Future research will benefit from assessing the validity of the SRQ in various clinical samples and how it compares to measures of sleep regularity calculated from prospective daily assessments.

The Prevalence and Associated Factors of Short Sleep Duration Among Nurses in Tertiary Public Hospitals in China: Findings from a National Survey

Background

Sleep is an essential component of health and well-being. Short sleep duration may negatively affect nurses’ health and patients’ safety.

Objective

To investigate the sleep duration and subjective satisfaction with sleep duration among nurses in tertiary public hospitals in China and to explore the associated factors.

Methods

This cross-sectional study was conducted between December 18 and 31, 2017 in 136 major public hospitals from 31 provinces in mainland China. An online anonymous questionnaire was delivered through WeChat. Totally 27,575 nurses completed the survey.

Results

The response rate was 95.46%. The mean reported total sleep duration was 6.67±0.97 hours per day. About 46.87% (n=12,924) reported having short sleep duration (SSD, less than 7 hours per day), and 27.63% (n=7618) were not satisfied with their sleep duration. In the SSD group, 45.67% (n=5902) were dissatisfied with their sleep duration. SSD was significantly associated with sociodemographic factors, including an older age, having more than one child, being divorced or separated, and job-related factors, including longer working hours, more night shifts and heavy workload.

Conclusion

Nearly half of the nurses in the public hospitals in China reported sleeping less than 7 hours, and more than one quarter were dissatisfied with their sleep duration. Interventions are needed to improve Chinese nurses’ sleep, including reducing working hours, night shifts or workload.

The effect of sleep-wake intraindividial variability in digital cognitive behaviour therapy for insomnia: A mediation analysis of a large-scale RCT

Study Objectives

Digital cognitive behavioral therapy for insomnia (dCBT-I) is an effective treatment for insomnia. However, less is known about mediators of its benefits. The aim of the present study was to test if intraindividual variability in sleep (IIV) was reduced with dCBT-I, and whether any identified reduction was a mediator of dCBT-I on insomnia severity and psychological distress.

Methods

In a two-arm randomized controlled trial (RCT), 1720 adults with insomnia (dCBT-I = 867; patient education about sleep = 853) completed the Insomnia Severity Index (ISI), the Hospital Anxiety and Depression Scale (HADS) and sleep diaries, at baseline and 9-week follow-up. Changes in IIV were analyzed using linear mixed modeling followed by mediation analyses of ISI, HADS, and IIV in singular sleep metrics and composite measures (behavioral indices (BI-Z) and sleep disturbance indices (SI-Z)).

Results

dCBT-I was associated with reduced IIV across all singular sleep metrics, with the largest between-group effect sizes observed for sleep onset latency (SOL). Reduced IIV for SOL and wake after sleep onset had the overall greatest singular mediating effect. For composite measures, SI-Z mediated change in ISI (b = −0.74; 95% confidence interval (CI) −1.04 to −0.52; 13.3%) and HADS (b = −0.40; 95% CI −0.73 to −0.18; 29.2%), while BI-Z mediated minor changes.

Conclusion

Reductions in IIV in key sleep metrics mediate significant changes in insomnia severity and especially psychological distress when using dCBT-I. These findings offer important evidence regarding the therapeutic action of dCBT-I and may guide the future development of this intervention.

Clinical trials

Name: Overcoming Insomnia: Impact on Sleep, Health and Work of Online CBT-I

Registration number: NCT02558647

URL: https://clinicaltrials.gov/ct2/show/NCT02558647?cond=NCT02558647&draw=2&rank=1

A systematic review of the association between sleep health and stress biomarkers in children

Sleep is intimately linked with the stress response system. While the evidence for this connection has been systematically reviewed in the adult literature, to our knowledge no studies have examined this relationship in young children. Recent scientific interest in understanding the effects of adverse environments in early childhood, including an emphasis on understanding the role of sleep, highlights the importance of synthesizing the current evidence on the relationship between sleep and the stress response system in early childhood. The aim of this systematic review is to examine the relationship between sleep health and biomarkers of physiologic stress (neuroendocrine, immune, metabolic, cardiovascular) in healthy children ages 0-12 y. Following PRISMA guidelines, we identified 68 empirical articles and critically reviewed and synthesized the results across studies. The majority of studies included school-age children and reported sleep dimensions of duration or efficiency. Overall, evidence of associations between sleep health and stress biomarkers was strongest for neuroendocrine variables, and limited or inconsistent for studies of immune, cardiovascular, and metabolic outcomes. Gaps in the literature include prospective, longitudinal studies, inclusion of children under the age of 5 y, and studies using objective measures of sleep.

Measuring sleep regularity: Theoretical properties and practical usage of existing metrics

STUDY OBJECTIVES

Sleep regularity predicts many health-related outcomes. Currently, however, there is no systematic approach to measuring sleep regularity. Traditionally, metrics have assessed deviations in sleep patterns from an individual's average. Traditional metrics include intra-individual standard deviation (StDev), Interdaily Stability (IS), and Social Jet Lag (SJL). Two metrics were recently proposed that instead measure variability between consecutive days: Composite Phase Deviation (CPD) and Sleep Regularity Index (SRI). Using large-scale simulations, we investigated the theoretical properties of these five metrics.

METHODS

Multiple sleep-wake patterns were systematically simulated, including variability in daily sleep timing and/or duration. Average estimates and 95% confidence intervals were calculated for six scenarios that affect measurement of sleep regularity: 'scrambling' the order of days; daily vs. weekly variation; naps; awakenings; 'all-nighters'; and length of study.

RESULTS

SJL measured weekly but not daily changes. Scrambling did not affect StDev or IS, but did affect CPD and SRI; these metrics, therefore, measure sleep regularity on multi-day and day-to-day timescales, respectively. StDev and CPD did not capture sleep fragmentation. IS and SRI behaved similarly in response to naps and awakenings but differed markedly for all-nighters. StDev and IS required over a week of sleep-wake data for unbiased estimates, whereas CPD and SRI required larger sample sizes to detect group differences.

CONCLUSIONS

Deciding which sleep regularity metric is most appropriate for a given study depends on a combination of the type of data gathered, the study length and sample size, and which aspects of sleep regularity are most pertinent to the research question.

Intraindividual variability in sleep schedule: effects of an internet-based cognitive-behavioral therapy for insomnia program and its relation with symptom remission

STUDY OBJECTIVES

Sleep schedule consistency is fundamental to cognitive-behavioral therapy for insomnia (CBT-I), although there is limited evidence suggesting whether it predicts treatment response. This analysis tested whether: (1) an Internet-based CBT-I program affects intraindividual variability (IIV) in sleep schedule and (2) sleep schedule IIV predicts insomnia symptom remission.

METHODS

This secondary analysis compares participants (N = 303) randomized to an Internet-based CBT-I program (SHUTi-Sleep Healthy Using the Internet) or Internet-based patient education (PE). Participants reported daily bedtimes and rising times on 10 online sleep diaries collected over 2 weeks at baseline and 9-week post-intervention assessment. Participants completed the Insomnia Severity Index (ISI) at post-assessment and 6-month follow-up; symptom remission was defined by ISI < 8. Mixed effects location scale modeling was used to examine the effect of SHUTi on bedtime and rising time IIV; a novel two-staged analysis examined the effect of bedtime and rising time IIV on insomnia symptom remission.

RESULTS

At post-assessment, SHUTi participants reported about 30% less bedtime and 32% less rising time variability compared to PE (ps < 0.03). Bedtime and rising time IIV was not independently associated with likelihood of insomnia symptom remission at the subsequent time point (ps > 0.18), nor did sleep schedule IIV moderate treatment response (ps > 0.12).

CONCLUSIONS

Findings demonstrate that an Internet-delivered CBT-I program can effectively increase users' sleep schedule consistency relative to an educational control. This consistency, however, was not related to treatment outcome when defined by insomnia symptom remission, suggesting that enforcing rigid sleep schedules for patients may not be necessary for treatment success.

CLINICAL TRIAL REGISTRATION

NCT00328250.

Sleep timing, sleep consistency, and health in adults: a systematic review

The objective of this systematic review was to examine the associations between sleep timing (e.g., bedtime/wake-up time, midpoint of sleep), sleep consistency/regularity (e.g., intra-individual variability in sleep duration, social jetlag, catch-up sleep), and health outcomes in adults aged 18 years and older. Four electronic databases were searched in December 2018 for articles published in the previous 10 years. Fourteen health outcomes were examined. A total of 41 articles, including 92 340 unique participants from 14 countries, met inclusion criteria. Sleep was assessed objectively in 37% of studies and subjectively in 63% of studies. Findings suggest that later sleep timing and greater sleep variability were generally associated with adverse health outcomes. However, because most studies reported linear associations, it was not possible to identify thresholds for “late sleep timing” or “large sleep variability”. In addition, social jetlag was associated with adverse health outcomes, while weekend catch-up sleep was associated with better health outcomes. The quality of evidence ranged from “very low” to “moderate” across study designs and health outcomes using GRADE. In conclusion, the available evidence supports that earlier sleep timing and regularity in sleep patterns with consistent bedtimes and wake-up times are favourably associated with health. (PROSPERO registration no.: CRD42019119534.)

Novelty This is the first systematic review to examine the influence of sleep timing and sleep consistency on health outcomes. Later sleep timing and greater variability in sleep are both associated with adverse health outcomes in adults. Regularity in sleep patterns with consistent bedtimes and wake-up times should be encouraged.

Sleep Inconsistency and Markers of Inflammation

Objective: Poor sleep is associated with higher levels of inflammatory biomarkers. Conventionally, higher average time awake, lower average time asleep, and lower sleep efficiency define poor sleep. Recent research suggests that, in addition to average sleep, sleep inconsistency is an important indicator of sleep dysfunction. The current study sought to extend our knowledge of the relationship between sleep and inflammation through an examination of sleep inconsistency and inflammatory biomarkers. Methods: Secondary analyses of the Survey of Midlife in the United States (MIDUS) sleep study were conducted. Five hundred thirty-three individuals completed nightly sleep diaries, actigraphy, and underwent a blood draw for the inflammatory biomarkers C-reactive protein, interleukin-6, and fibrinogen. Sleep inconsistency was derived from 7 consecutive nights of assessment and was operationalized as nightly fluctuations in the following variables: terminal wakefulness, number of awakenings, time in bed, sleep onset latency, and wake after sleep onset. Structural equation modeling was used to examine the influence of a latent average sleep and a latent sleep inconsistency variable on a latent inflammation variable. Models were subsequently adjusted for age, sex, BMI, health, and medication. Stratified models by sex were also analyzed. Results: The average sleep model would not converge. The sleep inconsistency model fit the data well. A significant positive association between the latent factors sleep inconsistency and inflammation was observed (β = 10.18, SE = 4.40, p = 0.021), suggesting inconsistent sleep is associated with higher levels of inflammatory biomarkers. When stratified by sex, the association between the latent sleep inconsistency factor and inflammation was significant for women (β = 1.93, SE = 0.82, p = 0.018), but not men (β = 0.20, SE = 0.35, p = 0.566). The association between sleep inconsistency and inflammation weakened following multivariate adjustment (β = 6.23, SE = 3.71, p = 0.093). Conclusions: Inconsistent sleep may be an associated feature of inflammatory dysfunction, especially in women. Future studies should build upon this preliminary work and examine these associations longitudinally and through treatment trials.

Sleep diary- and actigraphy-derived sleep parameters of 8-hour fast-rotating shift work nurses: A prospective descriptive study

BACKGROUND

Given the harmful effects of night shifts and rotating schedules on nurses' sleep and work performance, shift nurses' sleep patterns have been a research concern. Actigraphy involves acquisition of data using a movement sensor worn continuously on the nondominant wrist, typically for a week or more. Although actigraphy provides objective and accurate sleep data, sleep diaries have been a practical alternative. However, there is a lack of research on the agreement and consistency between the two methods of measuring sleep for shift work nurses. In addition, differences in sleep patterns by shift types among 8-hour fast-rotating shift work nurses has not yet been examined.

OBJECTIVES

To evaluate the agreement between the sleep diary and actigraphy methods for sleep assessment, and to compare sleep parameters of 8-hour fast-rotating shift work nurses according to shift type.

DESIGN

Descriptive and prospective study design.

SETTINGS

Two tertiary hospitals in Seoul, South Korea.

PARTICIPANTS

A total of 94 shift work nurses who wore actigraphy along with completing a sleep diary.

METHODS

Subjective and objective sleep parameters were recorded during a two-week period in a sleep diary and actigraphy, respectively. Bland-Altman plots and intraclass correlation coefficients were used to analyze the agreement between the two methods. Sleep parameters according to shift type were compared using the Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

Good agreement was observed between the sleep diary and the actigraphy data for total sleep time (intraclass correlation coefficients = 0.765 or 0.858) and variability in sleep time (intraclass correlation coefficients = 0.838). When compared to the actigraphy data, diary-derived data were overestimated by 41-45 min for total sleep time and 0.4% for variability in sleep time. There was a difference of 2-3 h of sleep quantity by shift type: 5.3-5.8 h for day shifts and 7.1-8.4 h for night shifts.

CONCLUSIONS

A sleep diary can function as an acceptable alternative to actigraphy for measuring shift work nurses' sleep patterns, specifically total sleep time and variability in sleep time. Given the high variability in sleep among shift work nurses, both personal and organizational efforts are required. Nurses should monitor their sleep quantity and develop their own regular sleep schedules to fit their work schedules. Hospitals should establish healthy schedules for nurses to guarantee sufficient sleep hours before work. Future research on shift work nurses' sleep should examine fluctuations in sleep duration.

Intraindividual variability in sleep and comorbid medical and mental health conditions

STUDY OBJECTIVES

Intraindividual variability (IIV) in sleep may be a risk factor for disease above the influence of mean sleep. Associations between IIV in sleep and risk for a comprehensive set of common medical and mental health conditions have not been assessed in a representative sample.

METHODS

This study examined mean and IIV in total sleep time (TST), sleep quality (SQ), sleep efficiency (SE), and circadian midpoint (CM) in 771 adults recruited for an epidemiological study. Participants completed 14 days of sleep diaries to assess TST, SQ, SE, and CM, after which they reported on medical conditions and mental health symptoms. Data were analyzed using logistic regression, and models controlled for gender, body mass index, age, and race.

RESULTS

Lower mean TST, SQ, and SE were related to increased odds of having gastrointestinal problems, depression, and anxiety. IIV in TST was related to increased odds of having neurological, breathing, and gastrointestinal problems, as well as pain and depression; all results held controlling for mean sleep and adjusting for false discovery rate. IIV in SQ and SE was not associated with odds of having any medical or mental health conditions after adjusting for false discovery rate, nor was IIV in CM or mean CM.

CONCLUSIONS

Confirming previous research, mean TST, SQ, and SE are related to risk for gastrointestinal problems, depression, and anxiety. IIV in TST may be a unique facet of disturbed sleep that is associated with increased risk for a diverse cluster of medical and mental health conditions.

Training Schedule and Sleep in Adolescent Swimmers

PURPOSE

Insufficient sleep duration may affect athletic performance and health. Inconsistent sleep pattern also has negative health effects, but studies on athletes' intraindividual sleep variability are scarce. The aim of this research was to compare total sleep time (TST) and variability (TST-variability), wakening after sleep onset, and sleep efficiency, during nights preceding early morning practices with other nights, and to investigate sleep characteristics of nights following a day with early morning only, evening only, or both a morning and an evening session in adolescent swimmers.

METHODS

Wrist-worn accelerometers were used to measure 1 week of sleep in 108 swimmers (mean age 16.1 [2.6] y) in Iceland. Adjusted regression analyses and linear mixed models were used to explore associations of training schedules with TST, TST-variability, wakening after sleep onset, and sleep efficiency.

RESULTS

Mean TST was 6:32 (h:min) (±39 min) and TST-variability was 63 minutes (±25 min). TST decreased and TST-variability increased with more early morning practices. TST preceding early training was 5:36 and 5:06 in <16- and ≥16-year-olds, respectively, shorter than on nights preceding later or no morning training (P < .001).

CONCLUSION

Swimmers have extremely short TST preceding early morning sessions and increased TST-variability with more early morning sessions.

Intraindividual variability in sleep and perceived stress in young adults

OBJECTIVES

Research suggests strong associations between habitual sleep parameters (eg, mean duration, timing, efficiency), perceived stress, and insomnia symptoms. The associations between intraindividual variability (IIV; night-to-night within-person variation) in sleep, perceived stress, and insomnia have not been explored. This study examined associations between IIV in subjectively and objectively determined sleep parameters and to perceived stress in young adults with and without insomnia.

DESIGN

Prospective longitudinal.

SETTING AND PARTICIPANTS

Participants were 149 college students (mean age = 20.2 [SD = 2.4], 59% female) either with insomnia (n = 81; 54%) or without insomnia (n = 68; 46%).

MEASUREMENTS

Participants completed 1 week of daily sleep diaries and actigraphy (to assess total sleep time [TST], sleep efficiency [SE], and circadian midpoint [CM]), the Perceived Stress Scale, and a diagnostic interview for determination of insomnia as part of a parent study.

RESULTS

Greater IIV in actigraphy-determined TST (but not SE or CM) was independently associated with greater perceived stress, regardless of insomnia status. Greater IIV in sleep diary-determined TST, SE, or CM was not associated with perceived stress. Insomnia status was the most robust predictor of elevated perceived stress. There was a significant interaction between IIV in sleep diary-determined TST and insomnia status on perceived stress: Only in those without insomnia was greater IIV in sleep diary-determined TST associated with higher perceived stress.

CONCLUSION

Maintaining a more consistent sleep duration may be associated with lower stress in college students. Future research is needed to clarify the directionality and implications of this association for treatment.

Sleep disturbance and physiological regulation among young adults with prior depression

Sleep disturbance and respiratory sinus arrhythmia (RSA) are well-known to be independently associated with depression. Yet, it remains unclear how sleep disturbance and impaired physiological regulation (indexed by RSA) may synergistically contribute to depression risk. The current study examined the relationship between sleep disturbance (duration, insomnia) on daily depressive symptoms, and whether RSA moderated this relationship in a sample of young adults with a history of depression. To examine hypotheses, participants (N = 102, ages 18-22) completed a laboratory socio-evaluative stressor task to assess RSA at rest and reactivity. Participants then completed daily measures of sleep duration, insomnia symptoms, and depressive symptoms for two weeks. For main effects, multilevel modeling indicated that shorter overall sleep duration (but not insomnia) predicted higher depressive symptoms, and individual fluctuations in insomnia symptoms (but not sleep duration) predicted higher levels of next-day depressive symptoms. Lower resting RSA, but not reactivity, potentiated these relationships. Individual differences in sleep disturbance (duration and insomnia) predicted prospective levels of depressive symptoms among individuals with lower physiological regulation (indexed by lower RSA), who were particularly vulnerable to the daily effects of sleep disturbance on depressed mood. These results suggest the need to examine both daily sleep disturbance and physiological regulation to understand who may be at greatest risk for depression.

Stress and sleep remain significant predictors of health after controlling for negative affect

Prior research has shown that the predictive power of a stress-health model can be improved by the addition of sleep as a predictor variable. However, negative affect (NA) may act as a confounding variable in stress-health relationships: a source of bias that potentially inflates the observed relationship between stress and health. The current study examines whether stress and sleep remain significant predictors of health after controlling for trait NA. An online survey containing well-established measures of stress, sleep, health, and NA was completed by 460 undergraduates. Hierarchical regression analyses revealed that stress and sleep remained significant predictors of self-reported health after controlling for the effects of NA. Our findings support the notion that stress-health models can be improved by the integration of sleep as an additional predictor variable and demonstrate that the stress/sleep-health relationships are not fully explained by dispositional NA. From a theoretical perspective, the inclusion of NA measures allows researchers to tease apart the unique contributions of predictor variables. This knowledge can subsequently be put to the test with greater confidence in the design of interventions that seek to improve health through stress reduction and improved sleep.

Direct and indirect associations of cognitive reappraisal and suppression with disease biomarkers

OBJECTIVE

Habitual use of emotion regulation strategies may influence physical health. We examined whether the tendencies to employ cognitive reappraisal and suppression were associated with health biomarkers, and whether stress and sleep quality mediated these associations. Design & main outcome measures: Using data from the Biomarkers substudy (n = 1255) of the national Midlife in the U.S. Study, we tested the hypothesis that there would be indirect, but not direct, associations of cognitive reappraisal and suppression to biomarker indicators of multisystem physiological dysregulation, that is, allostatic load (AL). We computed the proportion of biomarkers in the highest risk quartile within seven biological systems, and summed these scores to compute AL. Associations with the biological systems were also examined separately.

RESULTS

Neither reappraisal nor suppression was directly associated with AL or biomarker function in the seven biological systems. Suppression was indirectly associated with higher AL and greater dysregulation in the inflammatory, metabolic, and hypothalamic-pituitary-adrenal systems via its relations to stress and sleep, p < 0.05. Reappraisal was indirectly associated with lower AL and less metabolic and inflammatory dysregulation, ps<0.05.

CONCLUSIONS

Suppression and reappraisal may have different downstream health effects via stress, sleep, and biomarker expression, suggesting malleable emotion regulation strategies may be an important intervention target.

Sleep Health and Predicted Cardiometabolic Risk Scores in Employed Adults From Two Industries

STUDY OBJECTIVES

Sleep disorders and sleep deficiency can increase the risk for cardiovascular disease. Less is known about whether multiple positive attributes of sleep health known as the SATED (satisfaction, alertness, timing, efficiency, and duration) model, can decrease future cardiovascular disease risks. We examined whether and how a variety of indicators of sleep health predicted 10-year estimated cardiometabolic risk scores (CRS) among employed adults.

METHODS

Workers in two industries-extended care (n = 1,275) and information technology (IT; n = 577)-reported on habitual sleep apnea symptoms and sleep sufficiency, and provided 1 week of actigraphy data including nighttime sleep duration, wake after sleep onset (WASO), sleep timing, and daytime napping. Workers also provided biomarkers to calculate future cardiometabolic risk.

RESULTS

More sleep apnea symptoms predicted higher CRS in both industries. More sleep sufficiency, less WASO, and less daytime napping (having no naps, fewer naps, and shorter nap duration) were also linked to lower CRS, but only in the extended care workers. There was no effect of sleep duration in both industries. In the IT employee sample, shorter sleep duration (≤ 6 hours versus 6-8 hours) and more naps strengthened the link between sleep apnea and CRS.

CONCLUSIONS

Sleep health, measured by both subjective and objective methods, was associated with lower cardiometabolic disease risks among extended care workers (lower to middle wage workers). Sleep apnea was an important predictor of CRS; for the IT workers, the link between sleep apnea and CRS was exacerbated when they had poorer sleep health behaviors.

Genotype Influences Day-to-Day Variability in Sleep in Drosophila melanogaster

Patterns of sleep often vary among individuals. But sleep and activity may also vary within an individual, fluctuating in pattern across time. One possibility is that these daily fluctuations in sleep are caused by the underlying genotype of the individual. However, differences attributable to genetic causes are difficult to distinguish from environmental factors in outbred populations such as humans. We therefore employed Drosophila as a model of intra-individual variability in sleep using previously collected sleep and activity data from the Drosophila Genetic Reference Panel, a collection of wild-derived inbred lines. Individual flies had significant daily fluctuations in their sleep patterns, and these fluctuations were heritable. Using the standard deviation of sleep parameters as a metric, we conducted a genome-wide association study. We found 663 polymorphisms in 104 genes associated with daily fluctuations in sleep. We confirmed the effects of 12 candidate genes on the standard deviation of sleep parameters. Our results suggest that daily fluctuations in sleep patterns are due in part to gene activity.