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.

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.

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.

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.