How much does sleep vary from night-to-night? A quantitative summary of intraindividual variability in sleep by age, gender, and racial/ethnic identity across eight-pooled datasets.

Habitual sleep duration and efficiency vary widely by age, gender, and racial/ethnic identity. Despite growing research on the importance of night-to-night, intraindividual variability (IIV) in sleep, few studies have examined demographic differences in sleep IIV. The present study describes typical sleep IIV overall and by demographics among healthy sleepers. Eight datasets of healthy sleepers (N = 2,404; 26,121 total days of sleep data) were synthesised to examine age, gender, and racial/ethnic identity differences in sleep IIV measured via diaries, actigraphy, and electroencephalography (EEG). Sleep IIV estimates included the intraindividual standard deviation (iSD), root mean square of successive differences (RMSSD), coefficient of variation (CV), and a validated Bayesian Variability Model (BVM). There was substantial IIV in sleep across measurement types (diary, actigraphy, EEG) for both sleep duration (iSD: 85.80 [diary], 77.41 [actigraphy], 67.04 [EEG] minutes; RMSSD: 118.91, 108.89, 91.93 minutes; CV: 19.19%, 19.11%, 18.57%; BVM: 60.60, 58.20, 48.60 minutes) and sleep efficiency (iSD: 5.18% [diary], 5.22% [actigraphy], 6.46% [EEG]; RMSSD: 7.01%, 7.08%, 8.44%; CV: 5.80%, 6.27%, 8.14%; BVM: 3.40%, 3.58%, 4.16%). Younger adults had more diary and actigraphy sleep duration IIV. Gender differences were inconsistent. White and non-Hispanic/Latinx adults had less IIV in sleep duration and efficiency compared to racial/ethnic minority groups. Even among healthy sleepers, sleep varies widely from night-to-night. Like mean sleep, there also may be disparities in IIV in sleep by demographic characteristics. Study results help characterise normative values of sleep IIV in healthy sleepers.

Daily stress and sleep associations vary by work schedule: A between- and within-person analysis in nurses.

Nurses experience poor sleep and high stress due to demanding work environments. Night shift work is common among nurses and may exacerbate stress-sleep associations. We examined bidirectional associations between daily stress and sleep, and moderation by recent shift worker status and daily work schedule among nurses. Participants were 392 nurses (92% female; 78% White, mean age = 39.54, SD = 11.15) who completed 14 days of electronic sleep diaries and actigraphy. They simultaneously completed assessments of daily stress and work schedule upon awakening (day shift vs. night shift [work between 9 p.m.-6 a.m.] vs. off work). Participants were classified as recent night shift workers if they worked at least one night shift during the past 14 days (n = 101; 26%). In the entire sample, greater daily stress predicted shorter self-reported total sleep time and lower self-reported sleep efficiency that night. Shorter self-reported and actigraphy total sleep time and lower self-reported sleep efficiency predicted higher next-day stress. Compared with recent night shift workers, day workers reported higher stress after nights with shorter total sleep time. Stress-sleep associations mostly did not vary by nurses' daily work schedule. Sleep disturbances and stress may unfold in a toxic cycle and are prime targets for tailored interventions among nurses. Night shift workers may be less susceptible to the effects of short sleep on next-day stress. Research is needed to understand the short- and long-term effects of shift work and address the unique sleep challenges nurses face.

Daily Relations Between Stress and Electroencephalography-Assessed Sleep: A 15-Day Intensive Longitudinal Design With Ecological Momentary Assessments.

BACKGROUND: Recent studies have found bi-directional relations between stress and sleep. However, few studies have examined the daily associations between stress and electroencephalography (EEG) measured sleep. PURPOSE: This study examined the temporal associations between repeated ecological momentary assessments of stress and EEG-estimated sleep. METHODS: Ninety-eight international or interstate undergraduate students (Mage = 20.54 ± 1.64, 76.5% female, 84.7% Asian) reported their stress levels four times daily at morning awakening, afternoon, evening, and pre-bedtime across 15 consecutive days (>4,000 total observations). Next-day stress was coded as an average of morning, afternoon, and evening stress. Z-Machine Insight+ recorded over 1,000 nights EEG total sleep time (TST), sleep onset latency, wake after sleep onset, sleep efficiency (SE), slow-wave sleep (SWS), and rapid eye movement (REM) sleep duration. Multilevel models, adjusted for covariates (i.e., sociodemographic, health factors, and daily covariates) and lagged outcomes, tested the daily within- and between-level stress-sleep associations. RESULTS: After adjusting for covariates, within-person shorter TST (b = -0.11 [-0.21, -0.01], p = .04), lower SE (b = -0.02 [-0.03, 0.00], p = .04), less SWS (b = -0.38 [-0.66, -0.10], p = .008), and less REM sleep (b = -0.32 [-0.53, -0.10], p = .004) predicted higher next-day stress. Pre-bedtime stress did not predict same-night sleep. No significant results emerged at the between-person level. CONCLUSIONS: These findings demonstrate that poor or short sleep, measured by EEG, is predictive of higher next-day stress. Results for sleep architecture support the role of SWS and REM sleep in regulating the perception of stress. Given that only within-person effects were significant, these findings highlight the importance of examining night-to-night fluctuations in sleep affecting next-day stress and its impact on daytime functioning.

The Associations Between Daily Activities and Affect: a Compositional Isotemporal Substitution Analysis.

BACKGROUND: Daily activities are associated with affective experiences. A 24-h day can be separated into five mutually exclusive activity types: sleep, awake in bed, moderate-to-vigorous physical activity (MVPA), light-intensity physical activity (LIPA), and sedentary behavior (SB). Most research has examined these activities independently and not collectively, yet increased time in one activity must be offset by decreasing other activities. Using compositional isotemporal substitution analyses, this study examined the associations between time spent in daily activities and affect, including both high and low arousal positive and negative affect. METHOD: Across three separate studies, daily activities and affect were measured throughout 7-15 days (Mdays = 10) in 361 healthy community adults (72.5% females, Mage = 22.79 years). Activities were objectively assessed using accelerometry and self-reported affect was assessed using repeated ecological momentary assessments. Minutes spent in each activity and affect values across the three studies were averaged for each participant. RESULTS: Longer sleep duration at the expense of time awake in bed was associated with lower high arousal negative affect (e.g., nervousness, b = - 0.24, p = .007). More MVPA at the expense of LIPA or SB was associated with higher high arousal positive affect (e.g., happiness, b = 0.35, p = .027). Activity composition was not associated with low arousal positive or negative affect (all p ≥ .06). CONCLUSION: Associations between 24-h activity composition and affect differed based on types of activities, types of affect, and the interrelationships between activities within the composition. Findings can aid interventions to develop integrated guidance on the optimal activity patterns for mental health.

Daily Associations between Salivary Cortisol and EEG-Assessed Sleep: A 15-Day Intensive Longitudinal Study.

STUDY OBJECTIVES: Current evidence suggests that cortisol levels are bi-directionally associated with sleep. However, the daily, naturalistic cortisol-sleep associations remain unclear, as current evidence is mostly cross-sectional. This study tested whether pre-sleep cortisol predicts sleep duration and quality, and whether these sleep parameters predict the following day's diurnal cortisol slope using a 15-day intensive longitudinal design with electroencephalographic measures and saliva sampling. METHODS: Ninety-five young adults (Mage=20.48±1.59 years) provided saliva samples at awakening and pre-sleep over 14 consecutive days, providing 2,345 samples (85% viable). The Z-Machine Insight+ was used to record over 900 nights of total sleep time (TST) and sleep efficiency (SE). Multilevel models tested these data at the between- and within-person levels. RESULTS: Higher pre-sleep cortisol predicted shorter TST (p<.001) and lower SE (p<.001) at the within-person level. Individuals with shorter average TST (p =.007) or lower average SE (p<.001) had flatter diurnal cortisol slope, compared to those with longer average TST or higher average SE. Follow up analyses showed that individuals with shorter average TST (vs. longer average TST) had higher pre-sleep cortisol levels (p=.01). CONCLUSION: Our findings provide evidence that pre-sleep cortisol is associated with sleep duration and quality at the within-individual level. Furthermore, individuals with short or poor sleep had flatter diurnal cortisol slope. Although the effect sizes are small, these findings show the naturalistic associations between sleep and cortisol in a relatively healthy sample. These findings suggest that sleep maintains the regulation of the stress-response system, which is protective against mental and physical disorders.

Coping strategies predict daily emotional reactivity to stress: An ecological momentary assessment study.

BACKGROUND: Emotional reactivity predicts poor health and psychopathology. Despite its theoretical importance, little research has tested whether coping predicts emotional reactivity to stressors. We analyse three studies to test this hypothesis for negative (NA) and positive affect (PA) reactivity to daily stressors. METHODS: 422 Participants (72.5 % females, Mage = 22.79 ± 5.36) came from three longitudinal, ecological momentary assessment (EMA) studies across 7-15 days (ACES N = 190; DESTRESS N = 134; SHS N = 98). Coping was measured at baseline. NA, PA, and daily stressors were assessed via EMA. Mixed effects linear models tested whether coping predicted NA and PA reactivity, defined as their slope on within- and between-person daily stressors. RESULTS: Behavioural disengagement and mental disengagement coping predicted greater within-person NA reactivity across all studies (all p < .01, all f2 = 0.01). Denial coping predicted greater within-person NA reactivity in ACES and DESTRESS (both p < .01, f2 from 0.02-0.03) and between-person in ACES and SHS (both p < .01, f2 from 0.02 to 0.03). For approach-oriented coping, only active planning coping predicted lower within-person NA reactivity and only in DESTRESS (p < .01, f2 = 0.02). Coping did not predict PA reactivity (all p > .05). LIMITATIONS: Our findings cannot be generalised to children or older adults. Emotional reactivity to daily stressors may differ from severe or traumatic stressors. Although data were longitudinal, the observational design precludes establishing causality. CONCLUSIONS: Avoidance-oriented coping strategies predicted greater NA reactivity to daily stressors with small effect sizes. Few and inconsistent results emerged for approach-oriented coping and PA reactivity. Clinically, our results suggest that reducing reliance on avoidance-oriented coping may reduce NA reactivity to daily stressors.

Vulnerability to sleep-related affective disturbances? A closer look at dysfunctional beliefs and attitudes about sleep as a moderator of daily sleep-affect associations in young people.

STUDY OBJECTIVES: Sleep and affect are closely related. Whether modifiable cognitive factors moderate this association is unclear. This study examined whether Dysfunctional Beliefs and Attitudes about Sleep moderate the impact of sleep on next-day affect in young people. METHODS: Four hundred and sixty-eight young people (205 adolescents, 54.1% female, M ±â€¯SDage=16.92 ±â€¯0.87; 263 emerging adults, 71.9% female, M±SDage=21.29 ±â€¯1.73) self-reported sleep and affect, and wore an actigraph for 7-28 days, providing >5000 daily observations. Linear mixed-effects models tested whether Dysfunctional Beliefs and Attitudes about Sleep moderated daily associations between self-reported and actigraphic sleep duration, sleep efficiency, and next-day affect on between- and within-person levels. Both valence (positive/negative) and arousal (high/low) dimensions of affect were examined. Covariates included age, sex, race/ethnicity, day of week, and previous-day affect. RESULTS: Dysfunctional Beliefs and Attitudes about Sleep significantly moderated sleep and high arousal positive affect associations on between- but not within-person levels. Individuals with higher Dysfunctional Beliefs and Attitudes about Sleep (+1 SD) and lower average sleep duration (actigraphic: p = .020; self-reported: p = .047) and efficiency (actigraphic: p = .047) had significantly lower levels of high arousal positive affect. After adjusting for multiple comparisons, Dysfunctional Beliefs and Attitudes about Sleep did not moderate relationships between sleep duration and low arousal positive affect (p ≥ .340). CONCLUSIONS: Young people with more unhelpful beliefs about sleep and shorter, or poorer, sleep may experience dampened levels of high arousal positive affect. DBAS may constitute a modifiable factor increasing affective vulnerability on a global but not day-to-day level. Intervention studies are needed to determine if changing Dysfunctional Beliefs and Attitudes about Sleep may reduce sleep-related affect disturbances in young people.

Resilience to early family risk moderates stress-affect associations: A 14-day ecological momentary assessment study.

BACKGROUND: Resilience in children with early family life adversity is linked with successful adulthood psychological outcomes. However, whether resilience influences daily emotional responses to stress remains unclear. This study examined whether resilience capacity in the context of early family risks predicts better daily stress and affect outcomes during a stressful transition. METHODS: International and interstate undergraduates (N = 98; aged 18-25 years) were grouped as Resilient (high family risk, high resilience), Vulnerable (high family risk, low resilience), or Control (low family risk, average anxiety and depression). Daily negative (NA) and positive affect (PA), perceived stress, and stressors were assessed 4-times daily across 14 consecutive days (4333 total surveys; 73.7% completion rate). Affect reactivity was operationalized as the NA and PA slopes on perceived stress from each survey. RESULTS: The Resilient group did not differ from the Control group on all outcomes. The Vulnerable group reported significantly higher number of stressors, perceived stress levels, NA, and NA reactivity than the Resilient and Control groups (all p < .001); as well as significantly lower PA (p = .024) and PA reactivity (p = .003) than the Control group. LIMITATIONS: Our findings are not generalizable to other populations and cannot determine causality. CONCLUSIONS: Our findings suggest that resilience capacity is protective against the effects of early family risks on a daily basis. However, significant findings were limited to emotional distress outcomes and not supported for PA, suggesting resilience capacity may attenuate emotional distress but not positive emotions in response to stress in emerging adults with family risk.

A 14-day ecological momentary assessment study on whether resilience and early family risk moderate daily stress and affect on cortisol diurnal slope.

This study examined whether resilience capacity moderates the association of daily perceived stress and affect with cortisol diurnal slope among relocated emerging adults. Relocated undergraduates (N = 98; aged 18-25 years) were recruited from three groups: Resilient, Vulnerable, and Control. The Resilient group required Risky Family Questionnaire (RFQ) scores ≥ 29 and Brief Resilience Scale (BRS) scores ≥ 3.6. The Vulnerable group required RFQ scores ≥ 29 and BRS scores ≤ 3. The comparison Control group required RFQ scores ≤ 21 and T-scores < 60 on PROMIS anxiety and depression symptoms. Mixed-effects models were used to test the unique associations of perceived stress, negative affect, and positive affect x group interactions (predictors) on diurnal cortisol slope (outcome) across 14 consecutive days. The Resilient group did not moderate the associations between daily stress or affect on cortisol diurnal slope. Instead, both the Resilient and Vulnerable groups with early family risk, showed a steeper diurnal slope unique to higher stress and a flatter slope unique to higher negative affect. Results suggest that riskier early family life was significantly associated with altered cortisol diurnal slope outcomes to stress (i.e., demand) and negative affect (i.e., distress). These associations were not attenuated by current resilience capacity.

Daily coping moderates the relations between stress and actigraphic sleep: a daily intensive longitudinal study with ecological momentary assessments.

BACKGROUND: Theoretical models argue that coping reduces stress responses, yet no studies have tested whether coping moderates the prospective stress effects on sleep in daily life. PURPOSE: This study tested if coping moderates the stress-sleep association using a daily, intensive longitudinal design across 7-12 days. METHODS: 326 young adults (Mage = 23.24 ± 5.46) reported perceived stress and coping (problem-focused, emotional-approach, and avoidance) every evening between 20:00-02:00, providing over 2400 nights of sleep data and 3000 stress surveys from all participants. Actigraphy and sleep diaries measured total-sleep-time and sleep efficiency. Multilevel models tested the interaction effects of within- and between-person stress and coping on sleep. RESULTS: Within-person problem-focused and emotional-approach coping moderated the within-person stress effects on actigraphic total-sleep-time (both p = 0.02); higher stress predicted shorter total-sleep-time only during high use of problem-focused or emotional-approach coping (both p = 0.01). Between-person avoidance moderated the between-person stress effect on actigraphic total-sleep-time (p = 0.04); higher stress predicted shorter total-sleep-time for high avoidance coping (p = 0.02). Within-person emotional-approach coping buffered the between-person stress effect on actigraphic sleep efficiency (p = 0.02); higher stress predicted higher sleep efficiency for high emotional-approach coping (p = 0.04). CONCLUSIONS: This study showed that daily coping moderates the effects of evening stress on sleep that night. More efforts to cope with stress before bedtime had a short-term cost of shorter sleep that night. However, high use of emotional-approach coping buffered the impact of stress to promote sleep efficiency.

Bi-directional relations between stress and self-reported and actigraphy-assessed sleep: a daily intensive longitudinal study.

STUDY OBJECTIVES: Stress is associated with poor and short sleep, but the temporal order of these variables remains unclear. This study examined the temporal and bi-directional associations between stress and sleep and explored the moderating role of baseline sleep complaints, using daily, intensive longitudinal designs. METHODS: Participants were 326 young adults (Mage = 23.24 ± 5.46), providing >2,500 nights of sleep altogether. Prospective total sleep time (TST), sleep onset latency (SOL), wake after sleep onset (WASO), and sleep efficiency (SE) were measured using actigraphy and sleep diaries. Perceived stress was reported three times daily between: 11:00-15:00, 15:30-19:30, and 20:00-02:00. Sleep complaints were measured at baseline using the PROMIS sleep disturbance scale. Within- and between-person sleep and stress variables were tested using cross-lagged multilevel models. RESULTS: Controlling for covariates and lagged outcomes, within-person effects showed that higher evening stress predicted shorter actigraphic and self-reported TST (both p < .01). Conversely, shorter actigraphic and self-reported TST predicted higher next-day stress (both p < .001). Longer self-reported SOL and WASO (both p < .001), as well as lower actigraphic (p < .01) and self-reported SE (p < .001), predicted higher next-day stress. Between-person effects emerged only for self-reported TST predicting stress (p < .01). No significant results were found for the moderating role of baseline sleep complaints. CONCLUSIONS: Results demonstrated bi-directional relations between stress and sleep quantity, and a consistent direction of worse sleep quantity and continuity predicting higher next-day stress. Results highlighted within-individual daily variation as being more important than between-individual differences when examining sleep and daytime functioning associations.