Diurnal rhythms in plasma cortisol, insulin, glucose, lactate and urea in pigs fed identical meals at 12-hourly intervals

Diurnal rhythms in plasma cortisol, insulin, glucose, lactate and urea concentrations were investigated in eight catheterized pigs of approximately 35 kg BW. Pigs were fed isoenergetic/isoproteinic diets at a restricted level (2.5 x maintenance requirement for energy) in two daily rations (06:00 and 18:00 hours) in order to obtain equal intervals between feed intake. Preprandial plasma cortisol concentration was 22+/-3 ng/mL in the morning and 14+/-2 ng/mL in the evening (p<0.025), whereas the concentrations of insulin, glucose, lactate, and urea were similar. In the postprandial period in the morning (06:00-09:00 hours) plasma cortisol, insulin and lactate concentrations (expressed as the total area under the curve) were greater (p<0.001) compared to the evening (18:00-21:00 hours) by 100%, 42%, and 24%, respectively, while postprandial plasma glucose and urea concentrations were not affected by time of the meal. When postprandial plasma concentrations were expressed as a response over preprandial concentrations (decremental or incremental area under the curve), the diurnal rhythm was not observed for cortisol and glucose, persisted for insulin and lactate, and appeared for urea with a smaller postprandial urea response (p<0.05) in the morning compared to the evening. We conclude that the diurnal rhythm in plasma cortisol is independent of feeding whereas the diurnal rhythms in plasma insulin, lactate and urea are unveiled by the morning/evening meals in pigs. At equal 12-h intervals between meals, the postprandial responses of lactate and urea show diurnal variations, each in a specific manner, which suggest decreased postprandial efficiency of carbohydrate metabolism and increased postprandial efficiency of protein metabolism in the morning compared to the evening.     

Job strain and anger expression predict early morning elevations in salivary cortisol

OBJECTIVE: The objectives of this study were to test the hypothesis that high job demands and low job control (job strain) are associated with elevated free cortisol levels early in the working day and with reduced variability across the day and to evaluate the contribution of anger expression to this pattern. METHODS: One hundred five school teachers (41 men and 64 women) classified 12 months earlier as high (N = 48) or low (N = 57) in job strain according to the demand/control model sampled saliva at 2-hour intervals from 8:00 to 8:30 hours to 22:00 to 22:30 hours on a working day. Anger expression was assessed with the Speilberger State-Trait Anger Expression Inventory, and negative affect was also measured. RESULTS: Free cortisol was significantly elevated at 8:00 to 8:30 hours in the high job strain group but not at later times of the day or evening. After adjustment for age and negative affect, cortisol was an average of 21.7% higher early in the working day in the high job strain group. This effect was significantly greater in high job strain teachers, who also reported high anger-out. The cortisol decline from morning to evening was greater in the high than low job strain individuals. Independently of job strain, women had a higher cortisol concentration at 8:00 to 8:30 hours than men, whereas cortisol concentration was greater in men than women in the middle of the working day between 12:00 and 16:30 hours. CONCLUSIONS: Job strain is associated with elevated free cortisol concentrations early in the working day but not with reduced cortisol variability. The interaction with outward anger expression suggests that individual characteristics modulate the impact of chronic work stress on the hypothalamic-pituitary-adrenocortical system.     

Patterns of salivary cortisol levels can manifest work stress in emergency care providers

To develop objective assessments of work fatigue, we investigated the patterns of changes in salivary cortisol levels in emergency care providers working extended work shifts. Fourteen subjects, comprising seven physicians and seven physician assistants, provided unstimulated saliva samples at regular intervals over the course of a 24-h work shift and over their subsequent free day. There was a significant time effect, with early morning cortisol levels being significantly attenuated following the work shift. Native diurnal variations varied by gender, with the female subjects manifesting greater cortisol levels. Physicians also had higher cortisol profiles even though their wake–rest cycles were similar to those of the physician assistants. Our results suggest that temporal changes, as well as diurnal similarities, in the salivary cortisol patterns can reflect work-related stress and recovery. In particular, early morning cortisol levels may manifest individual reactivity to work stressors as well as sleep deprivation.     

Diurnal saliva cortisol levels and relations to psychosocial factors in a population sample of middle-aged swedish men and women

Whereas psychosocial risk factors increase the risk for disease, psychosocial resources reduce this risk. To examine a possible pathway for these effects, the relations between saliva cortisol levels and psychosocial factors were studied in a random sample of 257 men and women aged 30 to 64 years. Saliva samples were collected at home on waking, 30 min after waking, and in the evening. A flatter diurnal rhythm of cortisol, that is, lower deviations between awakening and evening cortisol levels, was related to high levels of psychosocial risk factors (cynicism, depression, and vital exhaustion), whereas a steeper diurnal rhythm was related to psychosocial resources (social support and coping), general health, and well-being (all p < .05). Our results support earlier suggestions that the capacity of the hypothalamic-pituitary-adrenal-axis to dynamically respond to stress is 1 pathway for observed effects of psychosocial factors regarding risk for disease development.     

Sequence and seasonal effects of salivary cortisol

Assessments of cortisol levels in saliva have been widely used by both researchers and clinicians as an index of adrenal functioning. Quarterly measurements of morning and evening cortisol levels were determined in a longitudinal study of 147 participants (72 women and 75 men) followed for 1 year each. The analysis of salivary cortisol revealed no significant gender or age differences in the sample. There was a sequence effect in quarterly cortisol values with a progressive decrease in serial measurements, especially notable in the morning values; as well as a seasonal variation in cortisol levels with significantly higher levels found in winter and fall, compared with spring and summer. The findings in this study suggest that repeated saliva sampling and seasonal variation in cortisol levels may independently affect adrenal response and, therefore, need to be accounted for in longitudinal studies.     

Social support at work, heart rate, and cortisol: a self-monitoring study

This study assessed the influence of work social support on self-monitored heart rate, blood pressure, and salivary cortisol recorded on 3 work days and 2 leisure days from 61 nurses and 32 accountants (40 men, 53 women). Heart rate and blood pressure were higher during the day at work than in the evening or on leisure days. Cortisol was higher on leisure than work days and was lower in the evening than in the day. Low social support at work was associated with elevated heart rate during the daytime and evening of work days, an effect that persisted after controlling for psychological distress, age, sex, smoking, and physical activity. Work social support was not related to cortisol on work days, but on leisure days cortisol was elevated among individuals reporting high social support. There were few differences between men and women, and no important occupational effects.     

Sequence and Seasonal Effects of Salivary Cortisol

Abstract

Assessments of cortisol levels in saliva have been widely used by both researchers and clinicians as an index of adrenal functioning. Quarterly measurements of morning and evening cortisol levels were determined in a longitudinal study of 147 participants (72 women and 75 men) followed for I year each. The analysis of salivary cortisol revealed no significant gender or age differences in the sample. There was a sequence effect in quarterly cortisol values with a progressive decrease in serial measurements, especially notable in the morning values, as well as a seasonal variation in cortisol levels with significantly higher levels found in winter and fall, compared with spring and summer. The findings in this study suggest that repeated saliva sampling and seasonal variation in cortisol levels may independently affect adrenal response and, therefore, need to be accounted for in longitudinal studies.     

Diurnal variation of the startle reflex in relation to HPA-axis activity in humans

Diurnal variation of baseline startle amplitude was examined in 14 normal inpatients on a research unit where behavioral activity and environmental stimuli were highly controlled. We tested a hypothesized association between diurnal variations of salivary cortisol and reflex amplitude by recording acoustic startle eyeblinks shortly before bedtime, when cortisol was near its lowest daily level, and just after awakening, when cortisol was at its peak. Results showed that startle eyeblinks were greater during evening than morning sessions, whereas the opposite was true for cortisol levels. Skin conductance levels and reaction time performance also increased from morning to evening. These findings are consistent with accumulating evidence suggesting a possible link between startle reactivity and hypothalamic-pituitary-adrenal axis activity, and an association between diurnal variations in endogenous arousal and startle amplitude.     

A prospective study of diurnal cortisol responses to the social experience of school transition in four-year-old children: anticipation, exposure, and adaptation

This study examined psychosocial influences on hypothalamic-pituitary-adrenal axis activity in 105 4-year-old children transitioning to primary school. Measuring before, during, and after school transition over a period of up to 12 months, salivary cortisol was assessed on awakening and early evening. Parents reported child temperament and teachers recorded adaptive behavior. Whilst cortisol at awakening and early evening increased from baseline to school transition, effects were not significant. A significant decrease occurred between transition and follow-up and from baseline to follow-up for both awakening and evening cortisol. Poorer effortful control was associated with high morning and steeper diurnal slope of cortisol at transition whilst surgency/extroversion was associated individually with greater morning and evening cortisol at transition and adaptation. Greater increase in internalizing social isolation during the first 6 months of school in more surgent/extrovert children predicted higher morning and evening cortisol at follow-up. This study is the first to explore these adaptive relationships over a 12-month period and supports social isolation over time as a key element in developmental endocrine activation.     

Chronotype and sex effects on sleep architecture and quantitative sleep EEG in healthy young adults

STUDY OBJECTIVES: To evaluate the influence of chronotype (morning types and evening types) on sleep stages and quantitative sleep electroencephalograms when constraints on the sleep schedule are minimal and when sex difference is taken into account. DESIGN: A 48-hour session in the laboratory, including 2 nights of polysomnography, preceded by 7 days of ambulatory actigraphy. SETTING: Chronobiology laboratory. PARTICIPANTS: Twenty-four healthy young subjects: 12 morning types and 12 evening types selected by questionnaire. Each group included 6 men and 6 women. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: A polysomnography night of 8 hours in duration was recorded according to preferred sleep schedule. Sleep-stage analysis revealed that morning types and evening types did not differ in sleep architecture. However, morning-type men showed a higher percentage of stage 1 sleep and lower sleep efficiency than evening-type men. Electroencephalogram spectral analysis was conducted in non-rapid eye movement sleep for 6 frequency bands. Morning types had more spectral power in low sigma (12-14 Hz) compared with evening types. The most robust difference between women and men was found in high sigma (14-16 Hz) and was not present between chronotypes. The decay rate of slow-wave activity (1-5 Hz) tended to be faster in morning types compared with evening types (P = .06). This rate was almost identical for women and men. CONCLUSIONS: These results agree with the hypothesis that homeostatic sleep regulation differs between morning types and evening types, with morning types showing indications of a higher rate of dissipation of sleep pressure during the night. Morningness-eveningness seems to affect sleep in a sex-specific manner, with men being more affected by their chronotype.     

Impact of gender, menstrual cycle phase, and oral contraceptives on the activity of the hypothalamus-pituitary-adrenal axis

OBJECTIVE: Results from animal and human studies suggest that disregulations of the hypothalamus-pituitary-adrenal (HPA) axis are involved in several behavioral, circulatory, endocrine, and immune disorders with clear-cut gender differences in disease prevalence. The aim of the present study was to investigate sex-specific HPA response patterns with a focus on the contribution of gonadal steroids as possible mediators. METHODS: A total of 81 healthy adults were investigated in the present study. Twenty men, 19 women in the follicular phase of the menstrual cycle, 21 women in the luteal phase, and 21 women using oral contraceptives (OC) were exposed to a brief psychosocial stress test (Trier Social Stress Test; TSST) and injected with 0.25 mg ACTH1-24 on consecutive days. Basal HPA activity was investigated by repeatedly measuring cortisol levels immediately after awakening, as well as in 30-minute intervals from 9:00 AM to 9:00 PM. Additionally, questionnaires were used to assess psychological state and trait parameters. RESULTS: Results show that the TSST induced significant increases in ACTH, salivary-free cortisol, total plasma cortisol, and heart rates, as well as increased wakefulness and reduced calmness in the total group. Significant group differences emerged for ACTH and salivary-free cortisol stress responses: Although men showed higher ACTH responses to the TSST compared with each of the three groups of women, salivary cortisol responses showed the following response pattern: Luteal = Men > Follicular = OC. The salivary cortisol responses to ACTH1-24 showed a similar response pattern: Luteal > Men > Follicular > OC. In contrast, total blood cortisol levels did not reveal any group difference between sexes or follicular versus luteal phase in either test. Although a similar salivary-free cortisol increase after awakening was found in the four groups, the circadian cortisol profile was significantly different throughout the first 4 hours of sampling. Questionnaire-derived psychological variables, as measured in the present study, could not explain the observed results. CONCLUSIONS: We conclude that gender, menstrual cycle phase, and OC use exert important effects on HPA responsiveness to psychosocial stress in healthy subjects. Although men seem to have a stronger hypothalamic drive in response to stressful stimulation than women, differences in salivary-free cortisol levels, at least in part, may be explained by estradiol-induced changes in corticosteroid-binding protein levels. ACTH and cortisol secretion is not affected by OC use per se but the amount of bioavailable unbound cortisol ("free") is greatly reduced in this group of women after stimulation. Inasmuch as none of these differences between the study groups emerged in total blood cortisol levels, we strongly advocate for the simultaneous measurement of free and total cortisol levels in future studies on HPA functioning.     

Diurnal courses of cortisol, pain, fatigue, negative mood, and stiffness in patients with recently diagnosed rheumatoid arthritis

To investigate the diurnal courses of cortisol and the daytime states: pain, fatigue, negative mood, and stiffness of patients with rheumatoid arthritis, as well as the association between the cortisol and state courses, 9 repeated measurementson 2consecutive days were taken in the real-life environment of 25 recently diagnosed patients (19 women, 6 men; mean age 55.2 years) and 28 healthy controls (20 women, 8 men; mean age 55.8 years). Patients showed a highly characteristic diurnal course of cortisol (F_{8, 15} = 7.4, p < .001) and a significant diurnal fatigue (F_{7, 18} = 2.6, p < .05) and early morning stiffness course (F3, 22 = 6.2, p < .01), but the temporal association between these courses was low. Daytime states, notably fatigue (r = 0.40, p < .05), were positively correlated with the early morning rise of cortisol and nighttime pain (r ≥ 0.53, p < .01) but not with cortisol level or inflammatory activity. Cortisol level and inflammatory activity were positively correlated (r = 0.47, p < .05). These results suggest that in patients with rheumatoid arthritis, cortisol has a strong endogenous rhythm that is not disturbed by inflammatory activity. It appears that diurnal fluctuations in fatigue and stiffness are independent of the circadian rhythm of cortisol or inflammatory activity, but rather reflect temporal changes as a consequence of sleep, rest, and physical activity throughout the day.     

Psychophysiological reactions to telework in female and male white-collar workers

Information technology has created greater flexibility and mobility for employees, such as teleworkers. However, research on stress and health is limited. This study investigated psychophysiological arousal in 26 highly educated white-collar workers (12 women and 14 men) while (a) working at the office, (b) working at home (telework), and (c) relaxing at home. Blood pressure was significantly higher during work at the office than when teleworking at home, and men had significantly elevated epinephrine levels in the evening after telework at home. It was assumed that the lower cardiovascular arousal during telework is due to different work tasks and that elevated epinephrine levels in men after telework are caused by continued work after normal working hours.     

Impact of acute sleep restriction on cortisol and leptin levels in young women

Sleep restriction alters hormone patterns and appetite in men, but less is known about effects on women. We assessed effects of overnight sleep restriction on cortisol and leptin levels and on appetite in young women. Participants' baseline sleep duration and eating habits were monitored for a week before the study. Salivary cortisol and leptin were sampled from fifteen healthy women (aged 18-25) during two consecutive days: first after a 10 h overnight sleep opportunity (Baseline day) and then after a night including only 3 h sleep (Post sleep-restriction day). Participants also completed appetite questionnaires on both days. Sleep restriction significantly reduced morning cortisol levels (p = 0.02), elevated morning leptin levels (p = 0.04), elevated afternoon/evening cortisol area under the curve values (p = 0.008), and slowed the decline in cortisol concentration during the day (p = 0.04). Hunger and craving scores did not differ significantly between days. A single night of restricted sleep affected cortisol rhythms and morning leptin levels in young women.     

Morningness and eveningness: the free cortisol rise after awakening in "early birds" and "night owls"

We investigated salivary cortisol profiles in the first hour after awakening in morning versus evening chronotypes. Chronotypes were defined by Horne and Ostberg's Owl-and-Lark-Questionnaire. In a sample of 112 healthy, day-active young men, we identified 9 morning and 29 evening chronotypes. Saliva samples were collected 0, 30, 45, and 60min after awakening on 2 consecutive days. Log-transformed cortisol levels were analyzed with General Linear Model procedures (GLMs) and awakening time and sleep duration were entered as covariates. On both days, a significant main effect of chronotype emerged (both p=0.02), and this effect could not be explained by differences in awakening time or sleep duration. The present data support the idea that morning relative to evening chronotypes might show higher cortisol levels in the first hour after awakening. In sum, individual chronotype should be acknowledged as one further possible source of interindividual variability in the cortisol rise after awakening.     

The relationship between long-term job strain and morning and evening saliva cortisol secretion among white-collar workers

The objective of this study was to assess long-term job strain impact on morning and evening salivary cortisol secretion. In all 77 white-collar workers (31% women; sample mean age, 42 years at baseline) volunteered to sample morning (immediately after waking up) and evening (10 p.m.) salivary cortisol for 7 consecutive days. By median split on aggregated self-reported isostrain from three consecutive questionnaires distributed in a period of approximately 3.5 years the participants were classified into a high or low long-term isostrain condition. Regardless of strain condition, there was a significant reduction in morning salivary cortisol secretion from the working week to the weekend, whereas evening salivary cortisol secretion showed no significant variation during the week. Although chronic isostrain did not affect the morning saliva cortisol measures, evening cortisol secretion was significantly elevated in the chronic high isostrain group throughout the whole week. The elevated evening cortisol measures associated with chronic high strain are concordant with the findings in other studies on long-term strain.     

Normative data on the diurnal pattern of the Karolinska Sleepiness Scale ratings and its relation to age,sex, work,stress, sleep quality and sickness absence/illness in a large sample of daytime workers

Self‐rated sleepiness responds to sleep loss, time of day and work schedules. There is, however, a lack of a normative reference showing the diurnal pattern during a normal working day, compared with a day off, as well as differences depending on stress, sleep quality, sex, age and being sick listed. The present study sought to provide such data for the Karolinska Sleepiness Scale. Participants were 431 individuals working in medium‐sized public service units. Sleepiness (Karolinska Sleepiness Scale, scale 1–9) was rated at six times a day for a working week and 2 days off (>90.000 ratings). The results show a clear circadian pattern, with high values during the morning (4.5 at 07:00 hours) and evening (6.0 at 22:00 hours), and with low values (3–4) during the 10:00–16:00 hours span. Women had significantly higher (0.5 units) Karolinska Sleepiness Scale values than men, as did younger individuals (0.3 units), those with stress (1.3 units above the low‐stress group) and those with poor sleep quality (1.0 units above those with qood sleep quality). Days off showed reduced sleepiness (0.7 units), while being sick listed was associated with an increased sleepiness (0.8 units). Multiple regression analysis of mean sleepiness during the working week yielded mean daytime stress, mean sleep quality, age, and sex as predictors (not sleep duration). Improved sleep quality accounted for the reduced sleepiness during days off, but reduced stress was a second factor. Similar results were obtained in a longitudinal mixed‐model regression analysis across the 7 days of the week. The percentage of ratings at Karolinska Sleepiness Scale risk levels (8 + 9) was 6.6%, but most of these were obtained at 22:00 hours. It was concluded that sleepiness ratings are strongly associated with time of day, sleep quality, stress, work day/day off, being ill, age, and sex.     

Women with PTSD have lower basal salivary cortisol levels later in the day than do men with PTSD: A preliminary study

Acute stress responses of women are typically more reactive than that of men. Women, compared to men, may be more vulnerable to posttraumatic stress disorder (PTSD). Whether there are differences between women and men with PTSD in levels of the stress hormone, cortisol, was investigated in a pilot study. Methods: women (n = 6) and men (n = 3) motor vehicle accident (MVA) survivors, with PTSD, had saliva collected at 1400 h, 1800 h, and 2200 h. Cortisol levels in saliva were measured by radioimmunoassay. An interaction between gender and time of sample collection was observed due to women's cortisol levels being lower and decreasing over time, whereas men's levels were higher and increased across time of day of collection. Results of this pilot study suggest a difference in the pattern of disruption of glucocorticoid secretion among women and men with PTSD. Women had greater suppression of their basal cortisol levels than did men; however, the diurnal pattern for cortisol levels to decline throughout the day was observed among the women but not the men.     

Responsiveness of the reproductive axis to a single missed evening meal in young adult males

Objectives: The male reproductive axis is responsive to energetic deficits, including multiday fasts, but little is known about brief periods of fasting (<24 hours). Reduced testosterone in low‐energy balance situations is hypothesized to reflect redirection of resources from reproduction to survival. This study tests the hypothesis that testosterone levels decrease during a minor caloric deficiency by assessing the effects of a single missed (evening) meal on morning testosterone in 23 healthy male participants, age 19–36. Methods: Participants provided daily saliva and urine samples for two baseline days and the morning following an evening fast (water only after 4 PM). Testosterone, cortisol, and luteinizing hormone were measured with enzyme immunoassays. Results: Fasting specimens had significantly lower overnight urinary luteinizing hormone (P = 0.045) and morning salivary testosterone than baseline (P = 0.037). In contrast to morning salivary testosterone, there was a significant increase in overnight urinary testosterone (P = 0.000) following the evening fast, suggesting an increase in urinary clearance rates. There was a marginal increase in overnight urinary cortisol (P = 0.100), but not morning salivary cortisol (P = 0.589). Conclusion: These results suggest the male reproductive axis may react more quickly to energetic imbalances than has been previously appreciated. Am. J. Hum. Biol., 2010. © 2010 Wiley‐Liss, Inc.     

Morningness-eveningness and early-morning salivary cortisol levels.

The purposes of this exploratory study were: (1) to describe a 2-h segment of the early-morning salivary cortisol levels of morning (M) and evening (E) types of healthy, day-active adults on one morning; and (2) to compare selected demographic and sleep characteristics. The sample consisted of 20 subjects, aged 23-39 years, 10 of each type. Measures included: morningness-eveningness questionnaire score, demographic information, self-report sleep characteristics, and self-report of well-being. Beginning with time of arising, seven salivary samples were collected at approximately 20-min intervals. Among the sleep variables, bedtime (p = 0.005), time of mid-sleep (p = 0.002), and arising time (p = 0.043) were later in the E group as compared to the M group. Six M and one E subject awoke spontaneously on the morning of sampling without an awakening aid (p = 0.018). Even though total hours of sleep were comparable between groups, E subjects reported feeling less rested in the morning (p = 0.019). Although mean M group salivary cortisol levels were greater than mean E group levels for each sampling time, there were no significant group differences. Eight M subjects reached a sampling period salivary cortisol peak by 50 min after arising, contrasted with six E subjects who reached their peak at that time. These preliminary findings suggest that E types demonstrate lower morning arousal and a delay in their early-morning peak of salivary cortisol relative to M types. Further study is needed to explore the relationship between M and E types, their sleep-wake patterns, and cortisol secretion patterns.