The effect of dawn simulation on the cortisol response to awakening in healthy participants

Selecting, implementing and evaluating control and placebo conditions in light therapy and light-based interventions

Introduction: Light profoundly influences human physiology, behaviour and cognition by affecting various functions through light-sensitive cells in the retina. Light therapy has proven effective in treating seasonal depression and other disorders. However, designing appropriate control conditions for light-based interventions remains a challenge.Materials and methods: This article presents a novel framework for selecting, implementing and evaluating control conditions in light studies, offering theoretical foundations and practical guidance. It reviews the fundamentals of photoreception and discusses control strategies such as dim light, darkness, different wavelengths, spectral composition and metameric conditions. Special cases like dynamic lighting, simulated dawn and dusk, complex interventions and studies involving blind or visually impaired patients are also considered.Results: The practical guide outlines steps for selection, implementation, evaluation and reporting, emphasizing the importance of α-opic calculations and physiological validation.Conclusion: In conclusion, constructing effective control conditions is crucial for demonstrating the efficacy of light interventions in various research scenarios.

The Efficacy of a Multimodal Bedroom-Based 'Smart' Alarm System on Mitigating the Effects of Sleep Inertia

Previous work has demonstrated the modest impact of environmental interventions that manipulate lighting, sound, or temperature on sleep inertia symptoms. The current study sought to expand on previous work and measure the impact of a multimodal intervention that collectively manipulated light, sound, and ambient temperature on sleep inertia. Participants slept in the lab for four nights and were awoken each morning by either a traditional alarm clock or the multimodal intervention. Feelings of sleep inertia were measured each morning through Psychomotor Vigilance Test (PVT) assessments and ratings of sleepiness and mood at five time-points. While there was little overall impact of the intervention, the participant's chronotype and the length of the lighting exposure on intervention mornings both influenced sleep inertia symptoms. Moderate evening types who received a shorter lighting exposure (≤15 min) demonstrated more lapses relative to the control condition, whereas intermediate types exhibited a better response speed and fewer lapses. Conversely, moderate evening types who experienced a longer light exposure (>15 min) during the intervention exhibited fewer false alarms over time. The results suggest that the length of the environmental intervention may play a role in mitigating feelings of sleep inertia, particularly for groups who might exhibit stronger feelings of sleep inertia, including evening types.

The importance of residential dusk and dawn light exposure for sleep quality, health, and well-being

Light exposure during twilight plays a critical role in the entrainment of the human circadian system. People are most often at home during dusk and dawn, and light exposure at home - either natural or from electric light - may therefore contribute substantially to sleep and well-being. However, very little research has focused on the effects of home lighting on sleep and well-being, and even less research has investigated the effects of light exposure during twilight. Therefore, a literature study was performed to collect studies on light exposure at home during dusk and dawn. Studies looking at light exposure during dusk and dawn have focused on either electric light intervention (i.e., dusk and dawn simulation) at home or in the laboratory or daylight exposure in the bedroom (i.e., the presence and type of curtains in the bedroom). Most research has focused on dawn simulation during the darker months of the year, often using sunrise alarms. In general, study results pointed to the importance of twilight light exposure at home for sleep and well-being. These results may depend on the characteristics of the user, such as age or chronotype.

Light therapy for sleep disturbance comorbid depression in relation to neural circuits and interactive hormones-A systematic review

AIM

To provide an overview of the evidence on the effect of light therapy on sleep disturbance and depression, identify the light-active neural and hormonal correlates of the effect of light therapy on sleep disturbance comorbid depression (SDCD), and construct the mechanism by which light therapy alleviates SDCD.

METHODS

Articles published between 1981 and 2021 in English were accessed using Science Direct, Elsevier, and Google Scholar following a three-step searching process via evolved keywords. The evidence level, reliability, and credibility of the literature were evaluated using the evidence pyramid method, which considers the article type, impact factor, and journal citation report (JCR) partition.

RESULTS

A total of 372 articles were collected, of which 129 articles fit the inclusion criteria and 44% were at the top of the evidence pyramid hierarchy; 50% were in the first quarter of the JCR partitions. 114 articles provided specific neural and hormonal evidence of light therapy and were further divided into three groups: 37% were related to circadian regulation circuits, 27% were related to emotional regulation circuits, and 36% were related to hormones.

CONCLUSIONS

First, neural and hormonal light-active pathways for alleviating sleep disturbance or depression were identified, based on which the neural correlates of SDCD were located. Second, the light responses and interactions of hormones were reviewed and summarized, which also provided a way to alleviate SDCD. Finally, the light-active LHb and SCN exert extensive regulation impacts on the circadian and emotional circuits and hormones, forming a dual-core system for alleviating SDCD.

Evaluation and update of the expert consensus guidelines for the assessment of the cortisol awakening response (CAR)

The cortisol awakening response (CAR) is frequently assessed in psychobiological (stress) research. Obtaining reliable CAR data, however, requires careful attention to methodological detail. To promote best practice, expert consensus guidelines on the assessment of the CAR were published (Stalder et al., 2016, PNEC). However, it is unclear whether these highly cited guidelines have resulted in actual methodological improvements. To explore this, the PNEC editorial board invited the present authors to conduct a critical evaluation and update of current CAR methodology, which is reported here. (i) A quantitative evaluation of methodological quality of CAR research published in PNEC before and after the guidelines (2013-2015 vs. 2018-2020) was conducted. Disappointingly, results reveal little improvement in the implementation of central recommendations (especially objective time verification) in recent research. (ii) To enable an update of guidelines, evidence on recent developments in CAR assessment is reviewed, which mostly confirms the accuracy of the majority of the original guidelines. Moreover, recent technological advances, particularly regarding methods for the verification of awakening and sampling times, have emerged and may help to reduce costs in future research. (iii) To aid researchers and increase accessibility, an updated and streamlined version of the CAR consensus guidelines is presented. (iv) Finally, the response of the PNEC editorial board to the present results is described: potential authors of future CAR research to be published in PNEC will be required to submit a methodological checklist (based on the current guidelines) alongside their article. This will increase transparency and enable reviewers to readily assess the quality of the respective CAR data. Combined, it is hoped that these steps will assist researchers and reviewers in assuring higher quality CAR assessments in future research, thus yielding more reliable and reproducible results and helping to further advance this field of study.

The circadian system modulates the cortisol awakening response in humans

Background

In humans, circulating cortisol usually peaks 30–60 min after awakening from nocturnal sleep, this is commonly referred to as the cortisol awakening response (CAR). We examined the extent to which the CAR is influenced by the circadian system, independent of behaviors including sleep.

Materials and methods

We examined the CAR in 34 adults (20 female) using two complementary multiday in-laboratory circadian protocols performed in dim light, throughout which behavioral factors were uniformly distributed across the 24-hour circadian cycle. Protocol 1 consisted of 10 identical consecutive 5-hour 20-minute sleep/wake cycles, and protocol 2 consisted of 5 identical consecutive 18-hour sleep/wake cycles. Salivary melatonin was used as the circadian phase marker (0° = dim light melatonin onset). During each sleep/wake cycle, salivary cortisol was measured upon scheduled awakening and 50-minutes later, with the change in cortisol defined as the CAR. Cosinor analyses were used to detect any significant circadian rhythmicity in the CAR. In secondary analyses, we adjusted the models for time awake before lights on, total sleep time, percent of rapid eye movement (REM) sleep, and percent of non-rapid eye movement (NREM) sleep.

Results

Both protocols revealed a similar circadian rhythm in the CAR, with peaks occurring at a circadian phase corresponding to 3:40–3:45 a.m., with no detectable CAR during the circadian phases corresponding to the afternoon. In addition to the sinusoidal component of the circadian rhythm, total sleep time was also associated with the CAR for protocol 1. The percent of sleep spent in REM or NREM sleep were not associated with the CAR in either protocol.

Conclusion

Our results show that the CAR exhibits a robust circadian rhythm that persists even after adjusting for prior sleep. Presuming that the CAR optimizes physiological responses to the anticipated stressors related to awakening, these findings may have implications for shift workers who wake up at unusual circadian phases. A blunted CAR in shift workers upon awakening in the evening may result in diminished responses to stressors.

The inflammatory immune system after wake up in healthy male individuals: A highly standardized and controlled study

This study investigates the effects of two light conditions on innate proinflammatory IL-6 cytokines and the cortisol awakening response. The between-subject experiment was conducted with 55 healthy adult-males (aged M_bright = 24.40, SD = 4.58; M_dim = 25.47, SD = 4.96) in a standardized sleep laboratory setting with 60-min light exposure post-awakening. Cortisol significantly increased with bright light exposure as compared to dim light (significant interaction effect). As for IL-6, the main effects of time and light condition were significant, however, the interaction effect between light and time was insignificant. Results replicate stimulatory effects of bright light on cortisol. In general, IL-6 concentrations decreased in both light conditions; however, bright light graphically showed higher concentrations 45–90 min after exposure in comparison to dim light, thus bright light has a potential stimulatory effect on IL-6 production.

Toward Sustainable Gentle Awakenings and Sleep Inertia Mitigation: A Low-Cost IoT-Based Adaptable Lighting and Temperature Control Approach

In this paper, our design aims to assist in sleep inertia reduction and avoid the startle response and irritation caused by alarm-made unpleasant wakeup stimuli. Thus, we propose an approach that employs a soft and alerting sunrise simulation, conditionally utilizes natural light, and appropriately lowers the bedroom temperature for awakening a sleeper tenderly and gradually to gain full alertness. This approach is inspired by known scientific implications confirming the effectiveness of lights and temperatures on wakefulness. In this regard, we present an economical do-it-yourself digital tech-assisted system for bedroom lighting and temperature control. The system design is based on the smartphone and Internet of Things (IoT) technology. We develop the hardware and software in the system for implementing three IoT-based control tasks. One is the tuning of artificial light brightness using the pulse width modulation technique. Another is the opening of the window curtain using stepper motor control and light detection. The other is the activation of the air-conditioning setting using an infrared remote control and temperature detection. We construct a testbed for conducting experiments. Experimental results demonstrate that the proposed system can execute task requirements satisfactorily. The proposed system is promising for achieving our goal. It embodies features of sustainability.

Study protocol for measuring the impact of (quasi-)monochromatic light on post-awakening cortisol secretion under controlled laboratory conditions

Cortisol secretion has a fundamental role in human circadian regulation. The cortisol awakening response (CAR) can be observed as a daily recurring sharp increase in cortisol concentration within the first hour after awakening and is influenced by environmental light conditions. The current work provides the study protocol for an ongoing research project that is intended to explore the spectral dependencies and to discuss measures of emotional state and cognitive functioning potentially related to the CAR. Based on a controlled within-subjects sleep laboratory study, the impact of a two-hour, (quasi-)monochromatic, post-awakening light exposure of different peak wavelength (applied from 6:00 to 8:00 am) on resulting CAR levels should be investigated in a systematic manner to eventually derive a corresponding spectral sensitivity model. As a secondary outcome, it should be explored whether a potentially light-enhanced cortisol secretion might also impact different measures of sleepiness, mood, and vigilance for certain wavelengths. The study protocol described in the present work discusses the various protocol steps using pilot data collected for two different wavelength settings (i.e., short-wavelength blue-light at λmax = 476 nm and long-wavelength red-light at λmax = 649 nm) experienced by a group of four healthy male adults at an average ± SD age of 25.25 ± 3.59 years.

Exposure to bedroom light pollution and cardiometabolic risk: A cohort study from Chinese young adults

Indoor light environment has altered dramatically and exposure to light at night (LAN) potential leads to the progression of cardiometabolic conditions. However, few studies have investigated the effect of bedroom LAN exposure on cardiometabolic risk. To estimate the associations between multi-period bedroom LAN exposure with cardiometabolic risk among Chinese young adults. We objectively measured multi-period bedroom LAN intensity using portable illuminance meter in an ongoing prospective cohort (n = 484). At one-year follow-up, 230 young adults provided fasting blood samples for quantification of cardiometabolic parameters. Cardiometabolic (CM)-risk score was derived as the sum of standardized sex-specific z-scores for waist circumference (WC), mean arterial pressure (MAP), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG) and homeostasis model assessment for insulin resistance (HOMA-IR), with HDL-C multiplied by - 1. Multivariate and univariable linear regression models were used to examine associations of multi-period bedroom LAN exposure with cardiometabolic risk. Exposure to higher bedroom LAN intensity is associated with 1.47-unit increase in CM-risk score (95% CI: 0.69-2.25; P < 0.001). Besides, post-bedtime light exposure was associated with elevated fasting insulin (PBL-1h: β = 0.06, 95% CI: 0.01-0.10; PBL-4h: β = 0.33, 95% CI: 0.19-0.47) and HOMA-IR (PBL-1h: β = 0.013, 95% CI: 0-0.03; PBL-4h: β = 0.07, 95% CI: 0.04-0.11) while pre-awake light exposure was associated with elevated total cholesterol (PAL-1h: β = 0.03, 95% CI: 0.02-0.04; PAL-2h: β = 0.02, 95% CI: 0.01-0.03), triglyceride (PAL-1h: β = 0.015, 95% CI: 0.01-0.02; PAL-2h: β = 0.01, 95% CI: 0-0.02) and low-density lipoprotein cholesterol (PAL-1h: β = 0.02, 95% CI: 0.01-0.03; PAL-2h: β = 0.02, 95% CI: 0.01-0.03). Among young adults, bedroom LAN exposure was significantly associated with higher cardiometabolic risk. Furthermore, different periods of bedroom light exposure have time-dependent effect on cardiometabolic risk. Further research is needed to confirm our findings and to elucidate potential mechanisms.

Daily cortisol awakening response and menstrual symptoms in young females

Menstrual symptoms include some rhythmical changes and stress perception but women differ in duration and severity of these symptoms. It is not known whether these differences are associated with cortisol awakening response (CAR). The aim of the current study was to follow young women daily for the CAR and menstrual parameters throughout the whole menstrual cycle. Healthy and regularly cycling young women (n = 16, 17 to 31-year-old) participated in the current study. The daily records of severity of problems (DRSP) was filled in daily by the participants. CAR was also assessed daily form the salivary samples collected at a 0-, 15-, 30- and 60-min post-awakening. In terms of daily awakening cortisol profiles, women had either 2-20 (n = 3), or 20-200 (n = 8) or 200-2000 (n = 5) ng/ml cortisol according to the median levels throughout their cycle. CAR was weakly and negatively correlated with DRSP scores but strongly and positively with oestradiol (R²  = 0.300; p = 0.000) and progesterone (R²  = 0.490; p = 0.000) concentrations. Individuals with higher oestradiol and progesterone concentrations did not have high DRSP scores. In conclusion, CAR had a very high between-subject difference but had a low within-subject difference throughout the days of menstrual cycle, suggesting that CAR is a relatively stable personal trait. Moreover, the interplay between cortisol, progesterone and oestradiol appears to be important for the severity of menstrual symptoms.

Effect of artificial dawn light on cardiovascular function, alertness, and balance in middle-aged and older adults

STUDY OBJECTIVES

When arising in the morning, many older people experience dizziness and difficulty maintaining proper balance, as the cardiovascular system is not able to compensate to the postural shift (standing) and maintain sufficient blood flow to the brain. Such changes in cardiovascular function are observed in young individuals exposed to a dawn simulation light. In this study, we examined whether exposure to a dawn simulation light could impact cardiovascular function and consequent changes in balance in middle-aged and older adults.

METHODS

Twenty-three participants (67.3 ± 8.8 y), 12 of whom reported a history of dizziness in the morning, underwent two overnight stays in our laboratory. During both nights, they slept in complete darkness, except for the last 30 minutes of one of the nights during which a dawn simulation light was used. Continuous blood pressure (BP) and heart rate (HR) were monitored. Subjective and objective alertness, salivary cortisol, and mobile and standing balance were examined upon arising.

RESULTS

Dawn simulation light decreased (33%) the amount of sleep before morning awakening, lowered BP (6.24 mmHg), and increased HR (0.93 bpm). Despite these changes in physiology, there was no significant impact of dawn simulation on subjective or objective alertness, measures of standing or ambulatory balance, morning cortisol awakening response, or cardiovascular function after awakening.

CONCLUSION

While the dawn simulation did cause an increase in wake and a change in cardiovascular function prior to morning arousal in older adults, we could find no evidence of a functional change in either cardiovascular function or balance upon standing.

CLINICAL TRIAL

Registered on Clinicaltrials.gov, #NCT02632318, https://clinicaltrials.gov/ct2/show/NCT02632318.

Morningness in German and Spanish students: a comparative study

Humans show pronounced individual differences in circadian orientation. Transcultural comparisons are interesting since biological (or environmental) factors together with cultural ones may contribute to differences in morningness–eveningness. We compared Spanish and German undergraduates using the Composite Scale of Morningness (CSM) to assess circadian preferences. Confirmatory and multiple groups confirmatory factor analysis were used to assess factor structure and structural invariance across countries. The results showed that a three‐factor model of morningness best characterises the CSM structure of both samples. Partial factorial invariance (factor loadings) across countries was demonstrated for the factors ‘morningness’ and ‘morning alertness’. Scores of both factors were higher in German students. Potential cultural and biological explanations for the differences are discussed. Copyright © 2007 John Wiley & Sons, Ltd.

Stress, the cortisol awakening response and cognitive function

There is evidence that stress-induced disruption of the circadian rhythm of cortisol secretion, has negative consequences for brain health. The cortisol awakening response (CAR) is the most prominent and dynamic aspect of this rhythm. It has complex regulatory mechanisms making it distinct from the rest of the cortisol circadian rhythm, and is frequently investigated as a biomarker of stress and potential intermediary between stress and impaired brain function. Despite this, the precise function of the CAR within the healthy cortisol circadian rhythm remains poorly understood. Cortisol is a powerful hormone known to influence cognition in multiple and complex ways. Studies of the CAR and cognitive function have used varied methodological approaches which have produced similarly varied findings. The present review considers the accumulating evidence linking stress, attenuation of the CAR and reduced cognitive function, and seeks to contextualize the many findings to study populations, cognitive measures, and CAR methodologies employed. Associations between the CAR and both memory and executive functions are discussed in relation to its potential role as a neuroendocrine time of day signal that synchronizes peripheral clocks throughout the brain to enable optimum function, and recommendations for future research are provided.

The effects of post-awakening light exposure on the cortisol awakening response in healthy male individuals

BACKGROUND

It is assumed that the expression of the cortisol awakening response (CAR) is modulated by light exposure during the peri-awakening period. While initial evidence supports this principal effect, the specific role of the spectral composition of light (brightness and wavelength) is still incompletely understood.

METHOD

Two counterbalanced within-subject experiments were conducted in a standardized sleep laboratory setting to investigate the effect of light intensity (study I; two days: dim vs. bright light) and spectral composition (study II; three days: red vs. blue vs. green light) on the CAR. Across studies, light exposure was conducted for one-hour post-awakening and the accuracy of CAR assessments (based on eight saliva samples) was well-controlled in line with recent guidelines.

RESULTS

The two studies revealed consistent effects of light exposure on the CAR. Specifically, an increased CAR was found after exposure to bright (vs. dim) light (study I; (F_{(3.7, 106.4)} = 11.93, p < .001, η²_p = .29) and following blue and green (vs. red) light exposure (study II; F_{(4.9, 194.6)} = 2.49, p = .037, η²_p = .10).

CONCLUSION

Our findings illustrate the crucial role of light intensity and wavelength for expression of the CAR, in line with current theoretical knowledge of underlying neurobiological mechanisms.

Effects of a dawn-dusk simulation on circadian rest-activity cycles, sleep, mood and well-being in dementia patients

Light is the most powerful "zeitgeber" signal to synchronize circadian sleep-wake cycles. In dementia, these rhythms are often fragmented - probably due to loss of neuronal function of the suprachiasmatic nuclei (the biological "master clock" in the brain) and/or weakness of external zeitgebers. We investigated the effects of a prototype dawn-dusk simulator (DDS) on circadian rest-activity cycles, sleep, mood and well-being in a balanced crossover design during fall and winter in 20 institutionalized patients with dementia (86 ± 6 y, 17 f). All participants had one baseline week followed by exposure to individually timed DDS over their beds for 7-8 weeks. They spent 8 weeks without DDS as a control. Mood, self-reliant daily activity, social behavior, agitation, and quality of life were assessed by standardized questionnaires and visual analogue scales, regularly rated by trained caregivers. Circadian and sleep characteristics of their rest-activity cycles were analyzed by actimetry over 17 weeks. DDS exposure led to significantly better mood in the morning hours after waking. The effects were most pronounced in the second 4 weeks with DDS, indicating that positive effects emerged gradually. Differences in circadian rest-activity cycles and sleep were mainly age-dependent. We found statistically significant correlations between measures of higher quality of life and better mood, greater alertness and circadian rhythm stability. We conclude that continuous, long-term application of dawn-dusk simulation at the sleep-wake transitions appears to increase external zeitgeber strength in institutionalized patients with dementia. The DDS may provide an effective, non-invasive tool to improve mood and ameliorate patients' quality of life.

Harnessing the Four Elements for Mental Health

Humans are intimately connected to nature, and our physical and mental health is influenced strongly by our environment. The "elements," classically described in humoral theory as Fire, Water, Earth, and Air, all may impact our mental health. In a contemporary sense, these elements reflect a range of modifiable factors: UV light or heat therapy (Fire); sauna, hydrotherapy, and balneotherapy (Water); nature-based exposure therapy and horticulture (Earth); oxygen-rich/clean air exposure; and breathing techniques (Air). This theoretical scoping review paper details the emerging evidence for a range of these elements, covering epidemiological and interventional data, and provides information on how we can engage in "biophilic" activities to harness their potential benefits. Interventional examples with emerging evidentiary support include "forest-bathing," heat therapy, sauna, light therapy, "greenspace" and "bluespace" exercise, horticulture, clay art therapy activities, and pranayamic yoga breathing exercises. Further robust research is however required to firmly validate many of these interventions, and to establish their therapeutic applications for the benefit of specific mental health disorders.

The Cortisol Awakening Response: Association With Training Load in Endurance Runners

The cortisol awakening response (CAR) is commonly used as a marker of psychological stress; however, it is unknown whether CAR is affected by regular physical-exercise-induced stress.

PURPOSE

To assess the relationship between training load and CAR.

METHODS

Recreational endurance athletes were recruited from local running clubs. Subjects (n = 15) completed training logs for 2 wk, with various training loads, including psychometric analysis (Recovery-Stress Questionnaire for Athletes). Subjects provided saliva samples each day immediately after waking and 30 min postwaking. Samples were analyzed for cortisol concentration via enzyme-linked immunosorbent assay and subsequently were analyzed for CAR and CAR%. Daily training load was calculated and analyzed as training impulse. Simple linear regression was used to assess the relationship between CAR and training impulse.

RESULTS

CAR (r² = .352, P = .025) and CAR% (r² = .373, P = .012) both showed a significant negative relationship with training load.

CONCLUSIONS

These results suggest that CAR is affected by regular exercise training loads in recreational athletes. It is recommended that future CAR research control for fitness level and exercise training load in physically active populations.

Cortisol response to awakening in prepubertal children and adults: Magnitude and variability

Within the first 30-45 min after awakening, there is a characteristic rise in cortisol that is referred to as cortisol awakening response (CAR). Over the past decades, the CAR has become an important biomarker, mainly because of its reported association with health and disease. Previous research showed that the CAR can already be reliably assessed in infants and children. Yet, earlier findings on the influence of age have been inconsistent, and limited attention has been devoted to prepubertal children. Here, we aimed to contrast the magnitude and stability of the CAR in prepubertal children and adults. To this end, 24 healthy adults between 35 and 50 years of age and 24 healthy children between 6 and 9 years of age collected four salivary cortisol samples within 45 min after awakening on 4 separate days, 2 weekdays, and 2 weekend days. Our results showed that there was a marked CAR on weekdays and weekend days in both adults and children. In children, however, the CAR was overall significantly attenuated relative to adults. Moreover, while the cortisol increases after awakening were, both on weekdays and weekend days, highly correlated in adults, there were no such associations in children. Together, these data suggest that the CAR is less pronounced and less stable in prepubertal children compared to adults. Such age differences need to be taken into account when using the CAR as a biomarker in clinical settings.

Exercise and the Cortisol Awakening Response: A Systematic Review

Background

The cortisol awakening response (CAR) has been used as a biomarker of stress response in a multitude of psychological investigations. While a myriad of biochemical responses have been proposed to monitor responses to exercise training, the use of CAR within the exercise and sports sciences is currently limited and is a potentially underutilized variable. Therefore, the purpose of this review was to collate studies that incorporate both exercise and CAR, in an effort to better understand (a) whether CAR is a useful marker for monitoring exercise stress and (b) how CAR may be most appropriately used in future research.

Methods

A systematic review of the literature was conducted, following PRISMA guidelines. Searches were conducted using PubMed, SportDISCUS, Scopus, and PsychInfo databases, using search terms related toCAR and exercise and physical activity.

Results

10,292 articles were identified in the initial search, with 32 studies included in the final analysis. No studies investigated the effects of laboratory-controlled exercise on CAR. Variable effects were observed, possibly due to inconsistencies in study design, methodology, population, and CAR analysis. The available literature suggests a threshold of exercise may be required to alter the HPA axis and affect CAR. Moreover, CAR may represent a combination of previous exercise load and upcoming stress, making current interpretation of field-based observational research challenging.

Conclusions

More research is needed to fully elucidate the influence of exercise on CAR and address a number of gaps in the literature, including controlling exercise load, consistent sample collection, and CAR calculation and analysis.

Use of Salivary Diurnal Cortisol as an Outcome Measure in Randomised Controlled Trials: a Systematic Review

Background

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis is associated with diverse adverse health outcomes, making it an important therapeutic target. Measurement of the diurnal rhythm of cortisol secretion provides a window into this system. At present, no guidelines exist for the optimal use of this biomarker within randomised controlled trials (RCTs).

Purpose

The aim of this study is to describe the ways in which salivary diurnal cortisol has been measured within RCTs of health or behavioural interventions in adults.

Methods

Six electronic databases (up to May 21, 2015) were systematically searched for RCTs which used salivary diurnal cortisol as an outcome measure to evaluate health or behavioural interventions in adults. A narrative synthesis was undertaken of the findings in relation to salivary cortisol methodology and outcomes.

Results

From 78 studies that fulfilled the inclusion criteria, 30 included healthy participants (38.5 %), 27 included patients with physical disease (34.6 %) and 21 included patients with psychiatric disease (26.9 %). Psychological therapies were most commonly evaluated (n = 33, 42.3 %). There was substantial heterogeneity across studies in relation to saliva collection protocols and reported cortisol parameters. Only 39 studies (50 %) calculated a rhythm parameter such as the diurnal slope or the cortisol awakening response (CAR). Patterns of change in cortisol parameters were inconsistent both within and across studies and there was low agreement with clinical findings.

Conclusions

Salivary diurnal cortisol is measured inconsistently across RCTs, which is limiting the interpretation of findings within and across studies. This indicates a need for more validation work, along with consensus guidelines.

Electronic supplementary material

The online version of this article (doi:10.1007/s12160-015-9753-9) contains supplementary material, which is available to authorized users.

Time to wake up: reactive countermeasures to sleep inertia

Sleep inertia is the period of impaired performance and grogginess experienced after waking. This period of impairment is of concern to workers who are on-call, or nap during work hours, and need to perform safety-critical tasks soon after waking. While several studies have investigated the best sleep timing and length to minimise sleep inertia effects, few have focused on countermeasures -especially those that can be implemented after waking (i.e. reactive countermeasures). This structured review summarises current literature on reactive countermeasures to sleep inertia such as caffeine, light, and temperature and discusses evidence for the effectiveness and operational viability of each approach. Current literature does not provide a convincing evidence-base for a reactive countermeasure. Caffeine is perhaps the best option, although it is most effective when administered prior to sleep and is therefore not strictly reactive. Investigations into light and temperature have found promising results for improving subjective alertness; further research is needed to determine whether these countermeasures can also attenuate performance impairment. Future research in this area would benefit from study design features highlighted in this review. In the meantime, it is recommended that proactive sleep inertia countermeasures are used, and that safety-critical tasks are avoided immediately after waking.

Stress in Persons with Dementia: Benefits of a Memory Center Day Program

Most persons with dementia are cared for by family members who are so overwhelmed that their mental and physical health declines. Adult day care programs (ADC) are growing in number to meet caregivers' needs for respite but little is known about their effect on enrollee mental health. We examined mental health of enrollees (stress, anxiety, mood, emotions) and arousal (blood pressure and salivary cortisol) from day program enrollment to 3 months following enrollment. Results showed significant decreases in morning cortisol level at 1 and 3 months (p=.047). Perceived stress decreased at 1 and 3 months measured by Perceived Stress Scale (p=.03) and Index of Clinical Stress (p=.01). Results provide support for ADC as a stress-reducing environment for individuals with mild to moderate cognitive impairment. Future studies should be conducted to examine which elements of ADC are beneficial.

Assessing the daily stability of the cortisol awakening response in a controlled environment

Background

Levels of cortisol, the end product of the hypothalamic-pituitary-adrenal (HPA) axis, display a sharp increase immediately upon awakening, known as the cortisol awakening response (CAR). The daily stability of the CAR is potentially influenced by a range of methodological factors, including light exposure, participant adherence, sleep duration and nocturnal awakenings, making inferences about variations in the CAR difficult. The aim of the present study was to determine the daily stability of multiple measurement indices of the CAR in a highly-controlled sleep laboratory environment. A secondary aim was to examine the association between objective sleep continuity and sleep architecture, and the CAR.

Methods

The CAR was assessed in 15 healthy normal sleepers (seven male, eight female, M_age = 23.67 ± 3.49 years) on three consecutive weekday mornings. Sleep was measured objectively using polysomnography. Saliva samples were obtained at awakening, +15, +30, +45 and +60 min, from which multiple CAR measurement indices were derived: cortisol levels at each time point, awakening cortisol levels, the mean increase in cortisol levels (MnInc) and total cortisol secretion during the measurement period. Morning 2 and Morning 3 awakening cortisol levels, MnInc and total cortisol secretion were compared and the relationship between Night 1 and Night 2 objective measures of sleep continuity and architecture, and the subsequent CAR, was also assessed.

Results

There were no differences in cortisol levels at each time point, or total cortisol secretion during the CAR period, between Morning 2 and Morning 3. Awakening cortisol levels were lower, and the MnInc was higher, on Morning 3. Morning 2 and Morning 3 awakening levels (r = 0.77) and total cortisol secretion (r = 0.82), but not the magnitude of increase, were positively associated.

Conclusions

The stability of the CAR profile and total cortisol secretion, but not awakening cortisol levels or the magnitude of increase, was demonstrated across two consecutive mornings of measurement in a highly-controlled environment. Awakening cortisol levels, and the magnitude of increase, may be sensitive to differences in daily activities.

Electronic supplementary material

The online version of this article (doi:10.1186/s40359-016-0107-6) contains supplementary material, which is available to authorized users.

Relationship between post-awakening salivary cortisol and melatonin secretion in healthy participants

We report the relationship between patterns of post-awakening salivary melatonin and cortisol secretion in healthy participants (n = 51; mean age 21.6 ± 5.0 years). Saliva samples were collected within the domestic setting, at 0-, 15-, 30-, and 45-min post-awakening on 2 consecutive typical weekdays. Analyses were undertaken on data with electronically verified sample timing accuracy (<5-min delay between awakening and the start of saliva sampling). Melatonin secretion declined linearly by an average of 29% within the first 45-min post-awakening. In contrast, there was a marked 112% surge in cortisol, characteristic of the cortisol awakening response. No day differences in melatonin or cortisol secretion were observed but melatonin concentrations were lower with later awakening. Despite contrasting post-awakening changes in these hormones, there was a lack of relationship between overall levels or patterns of melatonin and cortisol during this period.

Assessment of the cortisol awakening response: Expert consensus guidelines

The cortisol awakening response (CAR), the marked increase in cortisol secretion over the first 30-45 min after morning awakening, has been related to a wide range of psychosocial, physical and mental health parameters, making it a key variable for psychoneuroendocrinological research. The CAR is typically assessed from self-collection of saliva samples within the domestic setting. While this confers ecological validity, it lacks direct researcher oversight which can be problematic as the validity of CAR measurement critically relies on participants closely following a timed sampling schedule, beginning with the moment of awakening. Researchers assessing the CAR thus need to take important steps to maximize and monitor saliva sampling accuracy as well as consider a range of other relevant methodological factors. To promote best practice of future research in this field, the International Society of Psychoneuroendocrinology initiated an expert panel charged with (i) summarizing relevant evidence and collective experience on methodological factors affecting CAR assessment and (ii) formulating clear consensus guidelines for future research. The present report summarizes the results of this undertaking. Consensus guidelines are presented on central aspects of CAR assessment, including objective control of sampling accuracy/adherence, participant instructions, covariate accounting, sampling protocols, quantification strategies as well as reporting and interpreting of CAR data. Meeting these methodological standards in future research will create more powerful research designs, thus yielding more reliable and reproducible results and helping to further advance understanding in this evolving field of research.

Circadian cortisol and fatigue severity in relapsing-remitting multiple sclerosis

Cortisol is a key regulator of the immune system, energy metabolism, and stress, yet its relevance to fatigue experienced by people with relapsing-remitting multiple sclerosis (RRMS) remains uncertain. We examined cortisol secretory activity in RRMS and its association with fatigue severity between-individuals and within-individuals (day-to-day) using a case-control ecological momentary assessment design. While undergoing usual daily routines, 38 people with RRMS and 38 healthy control participants provided saliva samples at strategic time-points over 4 consecutive weekdays to measure the cortisol awakening response (CAR; 0, 30, and 45 min after awakening) and the diurnal cortisol slope (DCS; 6 quasi-random samples provided between 1000 h and 2000 h). Recalled fatigue was measured at baseline, and daily fatigue was measured as the mean average of momentary fatigue ratings provided alongside each DCS sample. Multilevel modeling found CAR output was greater in RRMS than controls, and recalled fatigue in RRMS was associated with both lower waking cortisol level and larger awakening response. Day-to-day, the CAR was not associated with same-day fatigue levels in RRMS. Cortisol appears to have a role in fatigue experienced in RRMS, but whether it is a causal factor remains unclear.

The psychophysiological and health corollaries of child problem behaviours in caregivers of children with autism and ADHD

BACKGROUND

The positive relationship between problem behaviours of children with additional complex needs and psychological distress in their caregivers has been widely evidenced. Fewer studies, however, have assessed the relationship between care recipients' problem behaviours and key physiological processes, relevant for the physical health status of their care providers. This study examined the psychological, endocrine and health corollaries of child problem behaviours in caregivers of children with autism and attention deficit hyperactivity disorder.

METHODS

Caregivers (n = 18) completed self-report measures of psychological distress, child problem behaviours and incidences of commonly occurring ailments. To capture important parameters of the basal diurnal cortisol pattern, caregivers collected saliva samples at waking, 30 min post waking, 1200 h and 2200 h on two consecutive weekdays.

RESULTS

Data revealed a positive relationship between caregivers' perceived levels of stress and problems with child conduct behaviours. In addition, caregivers who reported more problems with child emotional and hyperactivity behaviours displayed atypical cortisol patterns characterised by flatter diurnal cortisol slopes and reduced cortisol awakening response magnitude. Subjective reports of commonly occurring ailments were also greater in caregivers experiencing more problems with child emotional behaviours.

CONCLUSIONS

These findings have implications for interventions that aim to improve the psychophysiological well-being of the caregiver by targeting problem behaviours of the care recipient.

Altered entrainment to the day/night cycle attenuates the daily rise in circulating corticosterone in the mouse

The suprachiasmatic nucleus (SCN) is a circadian oscillator entrained to the day/night cycle via input from the retina. Serotonin (5-HT) afferents to the SCN modulate retinal signals via activation of 5-HT1B receptors, decreasing responsiveness to light. Consequently, 5-HT1B receptor knockout (KO) mice entrain to the day/night cycle with delayed activity onsets. Since circulating corticosterone levels exhibit a robust daily rhythm peaking around activity onset, we asked whether delayed entrainment of activity onsets affects rhythmic corticosterone secretion. Wheel-running activity and plasma corticosterone were monitored in mice housed under several different lighting regimens. Both duration of the light:dark cycle (T cycle) and the duration of light within that cycle was altered. 5-HT1B KO mice that entrained to a 9.5L:13.5D (short day in a T = 23 h) cycle with activity onsets delayed more than 4 h after light offset exhibited a corticosterone rhythm in phase with activity rhythms but reduced 50% in amplitude compared to animals that initiated daily activity <4 h after light offset. Wild type mice in 8L:14D (short day in a T = 22 h) conditions with highly delayed activity onsets also exhibited a 50% reduction in peak plasma corticosterone levels. Exogenous adrenocorticotropin (ACTH) stimulation in animals exhibiting highly delayed entrainment suggested that the endogenous rhythm of adrenal responsiveness to ACTH remained aligned with SCN-driven behavioral activity. Circadian clock gene expression in the adrenal cortex of these same animals suggested that the adrenal circadian clock was also aligned with SCN-driven behavior. Under T cycles <24 h, altered circadian entrainment to short day (winter-like) conditions, manifest as long delays in activity onset after light offset, severely reduces the amplitude of the diurnal rhythm of plasma corticosterone. Such a pronounced reduction in the glucocorticoid rhythm may alter rhythmic gene expression in the central nervous system and in peripheral organs contributing to an array of potential pathophysiologies.

The cortisol awakening response (CAR) in male children with autism spectrum disorder

Our ability to adapt to change is fundamental. The cortisol awakening response (CAR) is a sharp rise in cortisol 30min after waking to help prepare an individual for ensuing stress. Children with autism spectrum disorder (ASD) often have difficulty adapting to change. Exploration of the CAR is warranted; yet, the few studies investigating it are inconclusive. The CAR was investigated in 94 pre-pubertal male children 8-to-12years of age with ASD (46) and typical development (TD, 48). Salivary samples were collected over three diurnal cycles involving two morning samples: M1: Immediately upon Waking and M2: 30-min Post Waking (M2-M1=CAR). The magnitude of the CAR was measured by independent two sample t-tests, variability was measured using Levene's Test, the sequence of the CAR was analyzed by a linear mixed-effects model and proportion of children exhibiting a CAR by chi-square test of independence. There were no significant differences on the CAR between the groups based on magnitude (t(92)=-0.14, p=0.89, d=0.04), variability (F(45,47)=1.11, p=0.72, η(2)=0.11) or the sequence over three days (F(2,88)=0.26, p=0.77, η(2)=0.01). No significant differences were shown in the proportion of children exhibiting a CAR across the groups based on child (χ(2)(1)=0.02, p=0.89) or adult criterion (χ(2)(1)=1.82, p=0.18). Despite group differences in the regulation and responsivity of cortisol, the CAR is indistinguishable between children with and without ASD. Inconsistencies across studies may be due to age, criterion used, and diagnostic distinctions.

Anxiety, depression, stress, and cortisol levels in mothers of children undergoing maintenance therapy for childhood acute lymphoblastic leukemia

The purpose of this study was to compare anxiety, depression, and stress between mothers of children during maintenance treatment for acute lymphoblastic leukemia (ALL) and matched controls. Twenty-six mothers were recruited from the hematology unit at a children's hospital, and 26 mothers were recruited from the community. Participants were matched to their child's age and gender. Mothers completed the Hospital Anxiety and Depression Scale, the Perceived Stress Sale, and collected salivary cortisol 4 times a day for 3 consecutive days. Compared with mothers of healthy children, anxiety scores did not differ (P=.10), but depression scores were higher (P=.003) in mothers of children with ALL. More mothers in the ALL group scored above the cutoff of 7 indicating clinical anxiety (46%) and depressive symptoms (27%). A trend toward increased stress was found in mothers in the ALL group. No difference was found in overall daily cortisol (area under the curve), daily decrease in cortisol (slope), and cortisol awakening response. Mothers of children with ALL experienced emotional symptoms many months after the initial diagnosis.

Effects of dawn simulation on markers of sleep inertia and post-waking performance in humans

PURPOSE

To examine the effects of a simulated dawn during the last 30 min of sleep on the subsequent dissipation of sleep inertia and changes in simulated work and physical performance.

METHODS

Eight participants, who reported difficulty with morning waking, were administered in a random order to a control (C) and a dawn simulation (DS) trial (starting 30 min prior to waking). Subjective ratings of sleep quality and alertness were obtained alongside measures of cognitive performance (addition and reaction time tasks measured at 5, 30 and 75 min after waking at habitual workday times). Physical performance was also measured 35 min after waking using a self-paced cycling protocol.

RESULTS

After waking in DS, perceived sleep quality was 1.16 ± 0.89 (p = 0.01) points higher compared with C. Ratings of alertness were significantly higher in DS than C throughout the testing period (p = 0.04). Cognitive performance improved in both trials as time awake increased (p < 0.0005). On average, participants completed a greater number of additions in DS compared with C (69.5 ± 15.3 vs 66.9 ± 16.7, p = 0.03). Reaction times were also faster in DS compared with C (0.81 ± 0.07 s vs 0.86 ± 0.06 s, p < 0.0005). The self-paced time-trial was completed 21.4 s (4.7 %) quicker in DS (p = 0.07).

CONCLUSION

These data provide the first evidence that light exposure during the last 30 min of habitual sleep can increase subjective alertness and improve both cognitive and physical performance after waking.

Morning sleep inertia in alertness and performance: effect of cognitive domain and white light conditions

The transition from sleep to wakefulness entails a temporary period of reduced alertness and impaired performance known as sleep inertia. The extent to which its severity varies with task and cognitive processes remains unclear. We examined sleep inertia in alertness, attention, working memory and cognitive throughput with the Karolinska Sleepiness Scale (KSS), the Psychomotor Vigilance Task (PVT), n-back and add tasks, respectively. The tasks were administered 2 hours before bedtime and at regular intervals for four hours, starting immediately after awakening in the morning, in eleven participants, in a four-way cross-over laboratory design. We also investigated whether exposure to Blue-Enhanced or Bright Blue-Enhanced white light would reduce sleep inertia. Alertness and all cognitive processes were impaired immediately upon awakening (p<0.01). However, alertness and sustained attention were more affected than cognitive throughput and working memory. Moreover, speed was more affected than accuracy of responses. The light conditions had no differential effect on performance except in the 3-back task (p<0.01), where response times (RT) at the end of four hours in the two Blue-Enhanced white light conditions were faster (200 ms) than at wake time. We conclude that the effect of sleep inertia varies with cognitive domain and that it’s spectral/intensity response to light is different from that of sleepiness. That is, just increasing blue-wavelength in light may not be sufficient to reduce sleep inertia. These findings have implications for critical professions like medicine, law-enforcement etc., in which, personnel routinely wake up from night-time sleep to respond to emergency situations.

The effects of multivitamin supplementation on diurnal cortisol secretion and perceived stress

Recent evidence suggests that dietary intake of vitamins, in particular the B-vitamins including B6, B9 and B12 may have a number of positive effects on mood and stress. Given the effects of stress on a range of biological mechanisms including the endocrine system, it could be reasonably expected that multivitamin supplementation may also affect markers of these mechanisms such as diurnal cortisol secretion. In the current double-blind placebo-controlled study 138 adults (aged 20 to 50 years) were administered a multivitamin containing B-vitamins versus placebo over a 16-week period. Salivary cortisol measurements were taken at waking, 15-min, 30-min and at bedtime, at baseline, 8-weeks and 16-weeks. Perceived Stress (PSS) was measured at baseline, 8-weeks and 16-weeks, while blood serum measures of B6, B12 and homocysteine (HCy) as well as red cell folate (B9) were also collected at these time points. A significant interaction was found between treatment group and study visit for the Cortisol Awakening Response (CAR). Compared to placebo, at 16-weeks multivitamin supplementation was found to be associated with a near-significant trend towards an increased CAR. No significant differences in PSS were found between groups, with PSS increasing in both groups across the course of the study. Red cell folate was found to be significantly correlated with the CAR response at 16-weeks while HCy levels were not found to be associated with the CAR response, although HCy significantly correlated with waking cortisol levels at 8-weeks. A possible interpretation of the elevation in CAR associated with multivitamin supplementation is that this represents an adaptive response to everyday demands in healthy participants.

State variation in the cortisol awakening response

The cortisol awakening response (CAR) is a much studied but poorly understood aspect of the circadian pattern of cortisol secretion. A Scopus search of "cortisol" and "awakening" reveals 666 publications in this area since 1997 when it was first identified by Pruessner and colleagues as a "reliable biomarker of adrenocortical activity". The primary focus of the majority of these studies is centered on its utility as a biomarker associated with a range of psychosocial, physical and mental health variables. Such studies typically examine differences in the CAR (studied on 1 or 2 days) between healthy participants and other comparator groups of interest. Fewer studies (25 in our estimation) have examined correlates of day-to-day variation in the CAR in healthy participants, informing its role and regulation within the healthy circadian pattern of cortisol secretion. This is the first review to examine these studies which, although limited in number, offer a relatively coherent emerging story about state factors that influence the CAR and the impact of the CAR on daily functioning. Greater understanding of these issues helps illuminate the utility of the CAR as a promising biomarker in psychophysiological and epidemiological research. The review also highlights areas that require greater clarification and points to potentially fruitful areas of further research.

Effects of artificial dawn and morning blue light on daytime cognitive performance, well-being, cortisol and melatonin levels

Light exposure elicits numerous effects on human physiology and behavior, such as better cognitive performance and mood. Here we investigated the role of morning light exposure as a countermeasure for impaired cognitive performance and mood under sleep restriction (SR). Seventeen participants took part of a 48h laboratory protocol, during which three different light settings (separated by 2 wks) were administered each morning after two 6-h sleep restriction nights: a blue monochromatic LED (light-emitting diode) light condition (BL; 100 lux at 470 nm for 20 min) starting 2 h after scheduled wake-up time, a dawn-simulating light (DsL) starting 30 min before and ending 20 min after scheduled wake-up time (polychromatic light gradually increasing from 0 to 250 lux), and a dim light (DL) condition for 2 h beginning upon scheduled wake time (<8 lux). Cognitive tasks were performed every 2 h during scheduled wakefulness, and questionnaires were administered hourly to assess subjective sleepiness, mood, and well-being. Salivary melatonin and cortisol were collected throughout scheduled wakefulness in regular intervals, and the effects on melatonin were measured after only one light pulse. Following the first SR, analysis of the time course of cognitive performance during scheduled wakefulness indicated a decrease following DL, whereas it remained stable following BL and significantly improved after DsL. Cognitive performance levels during the second day after SR were not significantly affected by the different light conditions. However, after both SR nights, mood and well-being were significantly enhanced after exposure to morning DsL compared with DL and BL. Melatonin onset occurred earlier after morning BL exposure, than after morning DsL and DL, whereas salivary cortisol levels were higher at wake-up time after DsL compared with BL and DL. Our data indicate that exposure to an artificial morning dawn simulation light improves subjective well-being, mood, and cognitive performance, as compared with DL and BL, with minimal impact on circadian phase. Thus, DsL may provide an effective strategy for enhancing cognitive performance, well-being, and mood under mild sleep restriction.

Do state factors moderate the relationship between depressive symptoms and morning cortisol?

To fully capitalize on the utility of morning cortisol in biosocial studies of health and well-being researchers must carefully control for potential confounds. Recent reports have highlighted wake time, workday, and anticipatory negative emotions as regulators of intra-individual variation, with the potential to obscure cortisol-trait associations if not properly controlled. The purpose of this analysis is to examine the potential for trait-factors (i.e., depressive symptoms) to interact with state fluctuations in the prediction of morning cortisol. Saliva samples were collected from 56 working women at awakening and 30 min post awakening. Samples were collected on four consecutive days-two non-workdays followed by two workdays. Confirming prior research, morning cortisol levels were higher on work days and when individuals had early wake times. However, this relationship was strongest for women with fewer depressive symptoms. Similarly, only in women with fewer depressive symptoms was workday related to higher cortisol levels, and the anticipation of high negative affect related to steeper CARs and higher cortisol levels. Findings raise the possibility that certain populations may not be as physiologically sensitive to external regulatory cues, thus affecting intra-individual differences in HPA axis activity. Implications for future biobehavioral studies of depression and studies involving non-clinical samples are discussed.

Long-term stability of the cortisol awakening response over adolescence

The cortisol awakening response (CAR) has been widely assessed as a measure of hypothalamic-pituitary-adrenal (HPA) axis activity. Short-term stability is high; however, little is known about the long-term stability of the CAR. Because there are indications that development in adolescence influences HPA axis activity, this study investigated the stability of the CAR over adolescence. Participants were 229 boys and 181 girls from an adolescent general population sample who were assessed in three consecutive years, at mean ages of 15.0 (SD=0.4), 16.0 (SD=0.4) and 17.0 (SD=0.4) years. Cortisol was analyzed in saliva sampled at awakening, and 30 and 60min later. Stability was investigated both as rank-order and as mean-level stability. Effects of physical development during adolescence on stability were investigated as well. Rank-order stability was moderate to low, with tracking coefficients (interpretable as stability coefficients over time) of .15 (p<.001) for cortisol at awakening and .24 (p<.001) for cortisol 30 and 60min after awakening. Mean-levels of cortisol at awakening did not change, while the response to awakening increased over the years (linear slopes for cortisol 30 and 60min after awakening all p<.01). The increase may reflect the physical development of the adolescents. This is the first study, in a large population based sample, indicating that the rank-order of the CAR is stable over the course of several years. Interestingly, mean-levels of the cortisol response to awakening increased over the years, suggesting a maturation of HPA axis reactivity in relation to physical development over adolescence. Physical development should therefore be taken into account when investigating the CAR as a measure of HPA axis activity in adolescence.

Salivary cortisol in ambulatory assessment--some dos, some don'ts, and some open questions

The impact of stress on health and disease is an important research topic in psychosomatic medicine. Because research on hypothalamic-pituitary-adrenal (HPA) axis regulation under controlled laboratory studies lacks ecological validity, it needs to be complemented by a research program that includes momentary ambulatory assessment. The measurement of salivary cortisol offers the possibility to trace the free steroid hormone concentrations in ambulant settings. Therefore, in this article, we first discuss the role of salivary cortisol in ambulatory monitoring. We start with a brief description of HPA axis regulation, and we then consider cortisol assessments in other organic materials, followed by a presentation of common salivary markers of HPA axis regulation suitable for ambulatory assessment. We further provide an overview on assessment designs and sources of variability within and between subjects (intervening variables), acknowledge the issue of (non)compliance, and address statistical aspects. We further give an overview of associations with psychosocial and health-related variables relevant for ambulatory assessment. Finally, we deal with preanalytical aspects of laboratory salivary cortisol analysis. The relative simplicity of salivary cortisol assessment protocols may lead to an overoptimistic view of the robustness of this method. We thus discuss several important issues related to the collection and storage of saliva samples and present empirical data on the stability of salivary cortisol measurements over time.

The cortisol awakening response (CAR) in 2- to 4-year-old children: effects of acute nighttime sleep restriction, wake time, and daytime napping

The cortisol awakening response (CAR) is presumed critically important for healthy adaptation. The current literature, however, is hampered by systematic measurement difficulties relative to awakening, especially with young children. While reports suggest the CAR is smaller in children than adults, well-controlled research in early childhood is scarce. We examined whether robust CARs exist in 2- to 4-year-old children and if sleep restriction, wake timing, and napping influence the CAR (n = 7). During a 25-day in-home protocol, researchers collected four salivary cortisol samples (0, 15, 30, 45 min post-wake) following five polysomnographic sleep recordings on nonconsecutive days after 4 hr (morning nap), 7 hr (afternoon nap), 10 hr (evening nap), 13 hr (baseline night), and 16 hr (sleep restriction night) of wakefulness (20 samples/child). The CAR was robust after nighttime sleep, diminished after sleep restriction, and smaller but distinct after morning and afternoon (not evening) naps. Cortisol remained elevated 45 min after morning and afternoon naps. .

Salivary cortisol profiles in patients remitted from recurrent depression: one-year follow-up of a mindfulness-based cognitive therapy trial

Few studies have examined changes of diurnal cortisol profiles prospectively, in relation to non-pharmacological interventions such as mindfulness-based cognitive therapy (MBCT). Fifty-six patients remitted from recurrent depression (≥3 episodes) were included in an 8-week randomized controlled trial comparing MBCT plus treatment as usual (TAU) with TAU for depression relapse prophylaxis. Saliva samples (0, 15, 30, 45, 60 min post-awakening, 3 PM, 8 PM) were collected on six occasions (pre- and post-intervention, 3-, 6-, 9-, 12-month follow-up). Cortisol awakening response (CAR), average day exposure (AUCday) and diurnal slope were analyzed with mixed effects models (248 profiles, 1-6 per patient). MBCT (n = 28) and TAU groups (n = 28) did not significantly differ with respect to baseline variables. Intra-individual variability exceeded inter-individual variability for the CAR (62.2% vs. 32.5%), AUC(day) (30.9% vs. 23.6%) and diurnal slope (51.0% vs. 34.2%). No time, group and time by group effect was observed for the CAR and diurnal slope. A significant time effect (p = 0.003) was detected for AUCday, which was explained by seasonal variations (p = 0.012). Later wake-up was associated with lower CAR (-11.7% per 1-hour later awakening, p < 0.001) and lower AUCday (-4.5%, p = 0.014). Longer depression history was associated with dampened CAR (-15.2% per 10-year longer illness, p = 0.003) and lower AUCday (-8.8%, p = 0.011). Unchanged cortisol secretion patterns following participation in MBCT should be interpreted with regard to large unexplained variability, similar relapse rates in both groups and study limitations. Further research is needed to address the scar hypothesis of diminished HPA activity with a longer, chronic course of depression.

Seasonal differences in the diurnal pattern of cortisol secretion in healthy participants and those with self-assessed seasonal affective disorder

This study compared the daily pattern of free salivary cortisol secretion in winter and in summer between two groups; participants with self-assessed seasonal affective disorder (SAD) and age- and sex-matched healthy controls. Fifty-two participants completed the study with an equal number in each group. The diurnal pattern of cortisol secretion was assessed across two consecutive weekdays in summer, and two in winter, with conditions being counterbalanced. On each study day participants collected multiple saliva samples in the domestic setting to capture the cortisol awakening response (CAR) and declining levels across the day. In addition, perceived stress, anxiety, depression, state stress and state arousal were assessed using validated questionnaires. There was no evidence for any seasonal changes in psychological data or cortisol pattern for the healthy control population. In summer, self-assessed SAD and control participants had similar psychological and cortisol profiles. In winter however, SAD participants reported greater depression, stress and anxiety, and lower levels of arousal. Furthermore, the CAR was significantly attenuated in SAD participants during winter months. There was no difference in cortisol levels during the rest of the day between controls and SAD participants in winter. In line with the above findings and previous research, there was an inverse relationship between the increase in cortisol following awakening and a measure of seasonality in winter. Furthermore in winter, a general dysphoria construct correlated inversely with the CAR, indicating that participants reporting greater depression, stress and anxiety and lower arousal, exhibited lower CARs. In conclusion, during the shortened photoperiod in winter, the cortisol response to awakening is attenuated in participants with self-assessed SAD in comparison to controls. These findings contribute to the understanding of the physiology of SAD.

Associations between the cortisol awakening response and heart rate variability

The process of morning awakening is associated with a marked increase in cortisol secretion, the cortisol awakening response (CAR), as well as with a burst in cardiovascular (CV) activation. Whilst the CAR is largely driven by awakening-induced activation of hypothalamic-pituitary-adrenal axis, it is fine-tuned by direct sympathetic input to the adrenal gland. In parallel, awakening-induced activation of the CV system is associated with a shift towards dominance of the sympathetic branch of the autonomic nervous system. Moreover, the CAR, in common with trait-like heart rate variability (HRV), is widely reported to be associated with psychosocial variables and health outcomes. These commonalities led us to examine associations between the CAR and both concurrent awakening-induced changes and trait-like estimates in cardiovascular activity (heart rate (HR) and HRV). Self-report measures of difficulties in emotion regulation and chronic stress were also obtained. Forty-three healthy participants (mean age: 23 years) were examined on two consecutive weekdays. On both days, heart interbeat interval (IBI) data was obtained from sedentary laboratory recordings as well as from recordings over the peri-awakening period. Salivary free cortisol concentrations were determined on awakening and 15, 30, and 45min post-awakening on both study days. Data from a minimum of 36 participants were available for individual analyses. Results revealed significant awakening-induced changes in cortisol, HR and HRV measures; however, no associations were found between the simultaneous post-awakening changes of these variables. Similarly, awakening-induced changes in cortisol, HR and HRV measures were not significantly associated with perceived stress or measures of emotion regulation. However, the CAR was found to be significantly positively correlated with steady state measures of HR and negatively correlated with steady state measures of HRV, as determined during the laboratory sessions and the peri-awakening periods. This cross-sectional study indicates that, despite consistent associations between the CAR and indices of trait-like cardiovascular activity, the CAR is not related to concurrent changes of cardiac autonomic activation following awakening.

Basal cortisol levels in relation to dimensions and DSM-IV categories of depression and anxiety

The Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV classification may fail to adequately distinguish neuroendocrine factors involved in the etiology of depressive and anxiety disorders. Continuous phenotypic dimensions may correlate better with underlying neuroendocrine dysregulations. We compared the categorical DSM-IV diagnoses with a dimensional approach in the same group of outpatients with depressive (n=36), anxiety (n=18), and comorbid depressive and anxiety (n=19) disorders, who were free of psychotropic medication, and in 36 healthy controls. The Mood and Anxiety Symptom Questionnaire (MASQ) was used to measure the three dimensions of the tripartite model, i.e., anhedonic depression, anxious arousal, and general distress. The salivary cortisol awakening response (CAR) (0, 30, 45, and 60 min after awakening), and diurnal cortisol decline (11:00 h, 15:00 h, 19:00 h, and 23:00 h) were analyzed for linear and nonlinear associations. The CAR showed statistically significant nonlinear relationships with two MASQ dimensions, i.e., anhedonic depression and general distress, but no differences between DSM-IV categories. The diurnal cortisol decline was linearly related to the MASQ dimensions anhedonic depression and general distress and significantly higher AUC(diurnal) levels and a steeper slope were found in depressive patients compared to controls using DSM-IV categories. The present study shows that linear and nonlinear associations with salivary cortisol are detected when using phenotypic dimensions and may be complementary to phenotypic DSM-IV categories when doing neuroendocrine research.