The effect of shift work on different hematological parameters among healthcare workers.

Shift workers frequently experience alterations in their circadian rhythms, which are correlated with variations in hematological parameters. Changes in blood cells may be related to an individual's health status. Therefore, this study aimed to compare the relationship between shift work and changes in blood cells among a group of healthcare workers in Sri Lanka. A comparative cross-sectional study was conducted among healthcare workers, recruited by a stratified random sampling technique. Socio-demographic data were collected using a structured questionnaire. Venous blood samples were obtained and analyzed for the determination of total and differential blood cell counts. Descriptive statistics were used for the analysis of sociodemographic and hematological parameters. A sample of 37-day workers and 39 shift workers were included in the analysis. The mean ages (years) were not significantly different between the groups (36.8 ± 10.8 vs 39.1 ± 12.0; P = 0.371). Shift employees showed a significantly higher total mean white blood cell count (WBC) of 7548.75 mm-3 compared to day workers' 6869.19 mm-3 (P = 0.027). They also had higher mean absolute counts for all different WBC types (Neutrophils: 3949.2 vs 3557.7 , Lymphocyte: 2756.5 vs 2614.2 , Eosinophil: 317.6 vs 233.4 , Monocytes: 491.63 vs 432.51 , Basophils: 31.68 vs 29.22 ). Shift employees exhibited higher WBC counts than day workers at the same level of work experience. The length of shift work exposure revealed a positive link with neutrophil (r = 0.225 ) and eosinophil counts (r = 0.262 ), whereas these correlations were negative for day workers. Shift workers were associated with higher WBC counts in healthcare workers compared to their day-working counterparts.

Association between circadian rhythm disruption and polycystic ovary syndrome.

OBJECTIVE: To explore the association of circadian rhythm disruption with polycystic ovary syndrome (PCOS) and the potential underlying mechanism in ovarian granulosa cells (GCs). DESIGN: Multicenter questionnaire-based survey, in vivo and ex vivo studies. SETTING: Twelve hospitals in China, animal research center, and research laboratory of a women's hospital. PATIENTS/ANIMALS: A total of 436 PCOS case subjects and 715 control subjects were recruited for the survey. In vivo and ex vivo studies were conducted in PCOS-model rats and on ovarian GCs collected from women with PCOS and control subjects. INTERVENTION(S): The PCOS rat model was established with the use of testosterone propionate. MAIN OUTCOME MEASURE(S): Assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq), RNA sequencing, rhythmicity analysis, functional enrichment analysis. RESULT(S): There was a significant correlation between night shift work and PCOS. PCOS-model rats presented distinct differences in the circadian variation of corticotropin-releasing hormone, adrenocorticotropic hormone, prolactin, and a 4-h phase delay in thyrotropic hormone levels. The motif enrichment analysis of ATAC-seq revealed the absence of clock-related transcription factors in specific peaks of PCOS group, and RNA sequencing ex vivo at various time points over 24 hours demonstrated the differential rhythmic expression patterns of women with PCOS. Kyoto Encyclopedia of Genes and Genomes analysis further highlighted metabolic dysfunction, including both carbohydrate and amino acid metabolism and the tricarboxylic acid cycle. CONCLUSION(S): There is a significant association of night shift work with PCOS, and genome-wide chronodisruption exists in ovarian GCs.

Night shift work and cardiovascular disease biomarkers in female nurses.

BACKGROUND: Night shift work is associated with cardiovascular disease, but its associations with cardiovascular disease biomarkers are unclear. We investigated these associations in a study of female nurses. METHODS: We used data from the Nurses' Health Study II for total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, C-reactive protein (CRP), and fibrinogen. The sample sizes for our analysis ranged from 458 (fibrinogen) to 3574 (total cholesterol). From questionnaires, we determined the number of night shifts worked in the 2 weeks before blood collection and total years of rotating night shift work. We used quantile regression to estimate differences in biomarker levels by shift work history, adjusting for potential confounders. RESULTS: Nurses working 1 to 4 recent night shifts had median HDL cholesterol levels 4.4 mg/dL (95% confidence interval [CI]: 0.3, 7.5) lower than nurses without recent night shifts. However, working ≥5 recent night shifts and years of rotating night shift work were not associated with HDL cholesterol. There was no association between recent night shifts and CRP, but median CRP levels were 0.1 (95% CI: 0.0, 0.2), 0.2 (95% CI: 0.1, 0.4), and 0.2 (95% CI: 0.0, 0.4) mg/L higher among nurses working rotating night shifts for 1 to 5, 6 to 9, and ≥10 years compared with nurses never working rotating night shifts. These associations were attenuated when excluding postmenopausal women and women taking statins. We observed no associations between night shift work and other biomarkers. CONCLUSIONS: We found suggestive evidence of adverse short-term and long-term effects of night shift work on select cardiovascular disease biomarkers.

[SEASONAL FEATURES OF SEROTONIN IN BLOOD SERUM OF RATS AFTER PHYSICAL OVERWORK UNDER DESYNCHRONOSIS].

The content of serotonin in the blood serum of rats with light desynchronizes and physical fatigue in different seasons was investigated ву enzyme immunoassay. It was found that long-term light deprivation and exercise to complete depletion lowered levels of serotonin in the blood serum of rats in the winter and increased that of the spring season. At the same time, a dark deprivation and physical activity had no effect on this indicator.

Relationship between the change of ethological status and concentration of certain cytokines in blood in experimental desynchronosis under led lighting.

Changing the natural rhythm of day and night leads to the development of DS, disruption of coordinated muscular activity, adequate behavioral activity, a decrease of attention in the performance of night work by experts in various fields. Changes ethological status may potentiate or weaken the changes in the indices of immune status, contribute to the formation of allostatic load at desynchronosis. The purpose: To investigate the relationship between changes ethological status and concentration of certain cytokines in peripheral blood in experimental desynchronosis under LED lighting. Methods: The study was performed on 158 adult guinea pigs, which were randomly assigned into 2 groups: 1 group- animals in the conditions of standard fixed (12 h light / 12 h dark) LED lighting (SFSDO); 2 group- animals with jet lag in terms of LED lighting (DESSDO). Light desynchronosis created by keeping animals at clock coverage for 30 days. Behavioral activity was studied in the test «open field¼ cognitive function was assessed using aqueous «labyrinth¼ Morris. By ELISA was determined on the apparatus in the peripheral blood concentration of interleukin - 4 (IL-4), interferon-gamma (IFN-g), melatonin, cortisol via specific for guinea pig test systems. Results: It was found that in animals of DS in terms of LED lighting in the dynamics of 10-30 days of observation show signs of anxiety, depression orienting-exploratory behavior, reduce the long-term memory and learning ability, spatial orientation disorders. It found that when a jet lag LED lighting conditions for 10 days, 20 days and 30 days in peripheral blood melatonin concentration decreases, the concentration of cortisol rises. In peripheral blood decreased IL-4 concentrations of 20 and 30 days, reducing the concentration of IFN-g at 30 days. Based on the results of correlation analysis, ethological change status and progress of cognitive function with a decrease in the blood concentration of IL-4 and IFN-g, the concentration of melatonin increase cortisol levels. Conclusion: The results indicate that in experimental conditions in desynchronosis LED lighting changes ethological status are associated with the progression of immune status changes.

Biomarkers for circadian rhythm disruption independent of time of day.

Frequent shift work causes disruption of the circadian rhythm and might on the long-term result in increased health risk. Current biomarkers evaluating the presence of circadian rhythm disturbance (CRD), including melatonin, cortisol and body temperature, require 24-hr ("around the clock") measurements, which is tedious. Therefore, these markers are not eligible to be used in large-scale (human) studies. The aim of the present study was to identify universal biomarkers for CRD independent of time of day using a transcriptomics approach. Female FVB mice were exposed to six shifts in a clockwise (CW) and counterclockwise (CCW) CRD protocol and sacrificed at baseline and after 1 shift, 6 shifts, 5 days recovery and 14 days recovery, respectively. At six time-points during the day, livers were collected for mRNA microarray analysis. Using a classification approach, we identified a set of biomarkers able to classify samples into either CRD or non-disrupted based on the hepatic gene expression. Furthermore, we identified differentially expressed genes 14 days after the last shift compared to baseline for both CRD protocols. Non-circadian genes differentially expressed upon both CW and CCW protocol were considered useful, universal markers for CRD. One candidate marker i.e. CD36 was evaluated in serum samples of the CRD animals versus controls. These biomarkers might be useful to measure CRD and can be used later on for monitoring the effectiveness of intervention strategies aiming to prevent or minimize chronic adverse health effects.

Association between exposure to rotating night shift versus day shift using levels of 6-sulfatoxymelatonin and cortisol and other sex hormones in women.

The present study aims to compare 6-sulfatoxymelatonin (aMT6s) secretion patterns and levels of cortisol and sex hormones (estradiol, progesterone, DHEA, DHEAS, and testosterone) among rotating night-shift workers and day-shift workers. We performed a cross-sectional study in Cantabria (northern Spain) including 136 women (73 day-shift workers and 63 rotating night-shift workers). Blood and urine samples were obtained after two consecutive working days. Differences in means were estimated using ANCOVA, stratified by menopausal status, ovulation phase, and adjusted for season, age, body mass index, consumption of cigarettes in the last 24 h. aMT6s circadian rhythm was analyzed using the cosinor analysis. The present study showed that rotating night-shift workers had lower excretion of aMT6s than day-shift workers (mesor = 50.26 ng aMT6s/mg creatinine in women with rotating night shift versus 88.79 ng aMT6s/mg creatinine in women with day shift), lower fluctuation (amplitude = 45.24 ng aMT6s/mg creatinine in rotating night-shift workers versus 79.71 ng aMT6s/mg creatinine in day-shift workers), and a later acrophase (aMT6s peak time: 08:31 in rotating night-shift workers versus 07:13 h in day-shift workers). Additionally, women with rotating night shift had higher estradiol and progesterone levels, compared to day workers, especially in the follicular phase on the menstrual cycle.

Rapidly alternating photoperiods disrupt central and peripheral rhythmicity and decrease plasma glucose, but do not affect glucose tolerance or insulin secretion in sheep.

Disrupting circadian rhythms in rodents perturbs glucose metabolism and increases adiposity. To determine whether these effects occur in a large diurnal animal, we assessed the impact of circadian rhythm disruption upon metabolic function in sheep. Adult ewes (n = 7) underwent 3 weeks of a control 12 h light-12 h dark photoperiod, followed by 4 weeks of rapidly alternating photoperiods (RAPs) whereby the time of light exposure was reversed twice each week. Measures of central (melatonin secretion and core body temperature) and peripheral rhythmicity (clock and metabolic gene expression in skeletal muscle) were obtained over 24 h in both conditions. Metabolic homeostasis was assessed by glucose tolerance tests and 24 h glucose and insulin profiles. Melatonin and core body temperature rhythms resynchronized within 2 days of the last photoperiod shift. High-amplitude Bmal1, Clock, Nr1d1, Cry2 and Per3 mRNA rhythms were apparent in skeletal muscle, which were phase advanced by up to 3.5 h at 2 days after the last phase shift, whereas Per1 expression was downregulated at this time. Pparα, Pgc1α and Nampt mRNA were constitutively expressed in both conditions. Nocturnal glucose concentrations were reduced following chronic phase shifts (zeitgeber time 0, -5.5%; zeitgeber time 12, -2.9%; and zeitgeber time 16, -5.7%), whereas plasma insulin, glucose tolerance and glucose-stimulated insulin secretion were not altered. These results demonstrate that clock gene expression within ovine skeletal muscle oscillates over 24 h and responds to changing photoperiods. However, metabolic genes which link circadian and metabolic clocks in rodents were arrhythmic in sheep. Differences may be due to the ruminant versus monogastric digestive organization in each species. Together, these results demonstrate that despite disruptions to central and peripheral rhythmicity following exposure to rapidly alternating photoperiods, there was minimal impact on glucose homeostasis in the sheep.

Chronodisruption increases cardiovascular risk in zebrafish via reduced clearance of senescent erythrocytes.

The circadian clock and the hypoxic signaling pathway play critical roles in physiological homeostasis as well as in pathogenesis. The bi-directionality of the interaction between both pathways has been shown on physiological and only recently also on molecular level. But the consequences of a disturbed circadian rhythm for the hypoxic response and the cardiovascular system have never been addressed in any organism. Here we show that the hypoxic response of animals subjected to chronodisruption is reduced by approximately 30%, as reflected by decreased expression levels of hypoxia inducible factor 1 and its down-stream target genes erythropoietin, responsible for the generation of red blood cells (RBC) and vascular endothelial growth factor, which is essential for proper vascularization. Beside malformations of their vascular beds, chronodisrupted animals surprisingly revealed elevated numbers of senescent erythrocytes under normoxic conditions, due to a reduced clearance rate via apoptosis. Over-aged erythrocytes in turn are characterized by decreased oxygen transport capacities and an increased tendency for aggregation, explaining the higher mortality of chronodisrupted animals observed in our study. The present study shows for the first time that chronodisruption strongly interferes with the hypoxic signalling cascade, increasing the cardiovascular risk in zebrafish due to elevated proportions of senescent erythrocytes. The results might shed new light on the etiology of the increased cardiovascular risk observed among shiftworkers.

The influence of shift work on cognitive functions and oxidative stress.

Shift work influences health, performance, activity, and social relationships, and it causes impairment in cognitive functions. In this study, we investigated the effects of shift work on participants' cognitive functions in terms of memory, attention, and learning, and we measured the effects on oxidative stress. Additionally, we investigated whether there were significant relationships between cognitive functions and whole blood oxidant/antioxidant status of participants. A total of 90 health care workers participated in the study, of whom 45 subjects were night-shift workers. Neuropsychological tests were administered to the participants to assess cognitive function, and blood samples were taken to detect total antioxidant capacity and total oxidant status at 08:00. Differences in anxiety, depression, and chronotype characteristics between shift work groups were not significant. Shift workers achieved significantly lower scores on verbal memory, attention-concentration, and the digit span forward sub-scales of the Wechsler Memory Scale-Revised (WMS-R), as well as on the immediate memory and total learning sub-scales of the Auditory Verbal Learning Test (AVLT). Oxidative stress parameters were significantly associated with some types of cognitive function, including attention-concentration, recognition, and long-term memory. These findings suggest that night shift work may result in significantly poorer cognitive performance, particularly working memory.

The relationship between neutrophil lymphocyte ratio and non-dipper hypertension.

Non-dipper hypertension is associated with increased cardiovascular morbidity and mortality. Neutrophil/lymphocyte ratio (NLR) has been associated with poor outcomes in patients with cardiovascular diseases. However, little is known about the role of NLR in patients with non-dipper hypertension. In this study, NLR between dipper and non-dipper hypertensive patients was compared.This study included 80 hypertensive patients. Hypertensive patients were divided into two groups: 50 dipper patients (29 male, mean age 51.5 ± 8 years) and 30 non-dipper patients (17 male, mean age 50.6 ± 5.4 years). Transthoracic echocardiography and ambulatory 24-hour blood pressure monitoring were performed on all patients. No patient had a recent history of an acute infection or an inflammatory disease. Baseline NLR was measured by dividing neutrophil count to lymphocyte count. No statistically significant difference was found between the two groups in terms of basic characteristics. Mean NLR was significantly higher among persons with non-dipper compared with dipper patients (3.1 ± 0.95 vs. 1.8 ± 0.52, P < .001). Additionally, leukocytes and monocytes counts were higher in patients with non-dipper hypertension.In conclusion, our results suggest that higher NLR, an emerging marker of inflammation, has a positive correlation with blood pressure and is elevated in non-dippers compared with dippers.

Chronic circadian clock disruption induces expression of the cardiovascular risk factor plasminogen activator inhibitor-1 in mice.

Links between shift work and increases in metabolic risk factors for cardiovascular diseases have been documented in detail, although the underlying causes remain obscure. Plasminogen activator inhibitor-1 (PAI-1) is a key regulator of fibrinolysis that is also associated with an increased risk of cardiovascular diseases. We examined the effect of experimental chronic circadian clock disruption on PAI-1 expression in mice. Mice were exposed to chronic phase shifts and fed with a high-fat/high-sucrose diet. Chronic phase shifts resulted in increased plasma PAI-1 level through inducing PAI-1 mRNA expression and decreasing tissue-type plasminogen activator (tPA) mRNA expression in the liver. Chronic circadian clock disruption might induce hypofibrinolysis and increase the risk of cardiovascular events by inducing the PAI-1 gene expression in obese individuals.

Effect of a phase advance and phase delay of the 24-h cycle on energy metabolism, appetite, and related hormones.

BACKGROUND: The disruption of the circadian system has been associated with the development of obesity. OBJECTIVE: We examined the effects of circadian misalignment on sleep, energy expenditure, substrate oxidation, appetite, and related hormones. DESIGN: Thirteen subjects [aged 24.3 ± 2.5 (mean ± SD) y; BMI (in kg/m²): 23.6 ± 1.7 (mean ± SD)] completed a randomized crossover study. For each condition, subjects stayed time blinded in the respiration chamber during 3 light-entrained circadian cycles that resulted in a phase advance (3 × 21 h) and a phase delay (3 × 27 h) compared with during a 24-h cycle. Sleep, energy expenditure, substrate oxidation, and appetite were quantified. Blood and saliva samples were taken to determine melatonin, glucose, insulin, ghrelin, leptin, glucagon-like peptide 1 (GLP-1), and cortisol concentrations. RESULTS: Circadian misalignment, either phase advanced or phase delayed, did not result in any changes in appetite or energy expenditure, whereas meal-related blood variables (glucose, insulin, ghrelin, leptin, and GLP-1) followed the new meal patterns. However, phase-advanced misalignment caused flattening of the cortisol-secretion pattern (P < 0.001), increased insulin concentrations (P = 0.04), and increased carbohydrate oxidation (P = 0.03) and decreased protein oxidation (P = 0.001). Phase-delayed misalignment increased rapid eye movement sleep (P < 0.001) and the sleeping metabolic rate (P = 0.02), increased glucose (P = 0.02) and decreased GLP-1 (P = 0.02) concentrations, and increased carbohydrate oxidation (P = 0.01) and decreased protein oxidation (P = 0.003). CONCLUSIONS: The main effect of circadian misalignment, either phase advanced or phase delayed, is a concomitant disturbance of the glucose-insulin metabolism and substrate oxidation, whereas the energy balance or sleep is not largely affected. Chronically eating and sleeping at unusual circadian times may create a health risk through a metabolic disturbance. This trial was registered at the International Clinical Trials Registry Platform (http://apps.who.int/trialsearch/) as NTR2926.

Rest-activity disturbances in children with septo-optic dysplasia characterized by actigraphy and 24-hour plasma melatonin profiles.

INTRODUCTION: A trial of melatonin treatment in children with septo-optic dysplasia (SOD) and sleep disruption is accepted clinical practice in many centers. However, no objective measurements of sleep/activity patterns with 24-h melatonin profiles have been published for these individuals, and the pathophysiological basis underlying sleep disorders in SOD remains largely unknown. METHODS: We studied six children with rest-activity disturbances and SOD. All wore an Actiwatch-Mini (a noninvasive method of detecting and recording movement intensity) for 2 wk and were admitted to hospital for a 24-h period during which hourly measurements of serum melatonin were taken. Sleep data were analyzed in conjunction with a detailed sleep diary. Ethical approval was obtained for these studies. RESULTS: Two children produced virtually no melatonin throughout the 24-h period of measurement and had fragmented sleep patterns with no evidence of a non-24-h sleep-wake disorder or delayed sleep-phase disorder. One child had a normal melatonin profile despite actigraphy showing an arrhythmic sleep pattern. The remaining three children had fragmented sleep, with two having normal melatonin profiles and one having a modest increase in daytime melatonin concentrations, making the timing of dim-light melatonin onset difficult to discern. CONCLUSIONS: There is considerable variation in timing and amount of melatonin secretion in these children. Surprisingly, none of the children had either actigraphic or melatonin profile evidence of a non-24-h sleep-wake disorder or delayed sleep-phase disorder. Understanding the heterogeneous nature of underlying sleep disorders in this group of children is important and has implications for their management.

Circadian disruption, Per3, and human cytokine secretion.

Circadian disruption has been linked with inflammation, an established cancer risk factor. Per3 clock gene polymorphisms have also been associated with circadian disruption and with increased cancer risk. Patients completed a questionnaire and provided a blood sample prior to undergoing a colonoscopy (n = 70). Adjusted mean serum cytokine concentrations (IL-6, TNF-alpha, gamma-INF, IL-1ra, IL-1-beta, VEGF) were compared among patients with high and low scores for fatigue (Multidimensional Fatigue Inventory), depressive symptoms (Beck Depression Inventory II), or sleep disruption (Pittsburgh Sleep Quality Index), or among patients with different Per3 clock gene variants. Poor sleep was associated with elevated VEGF, and fatigue-related reduced activity was associated with elevated TNF-alpha concentrations. Participants with the 4/5 or 5/5 Per3 variable tandem repeat sequence had elevated IL-6 concentrations compared to those with the 4/4 genotype. Biological processes linking circadian disruption with cancer remain to be elucidated. Increased inflammatory cytokine secretion may play a role.

Delayed onset of the diurnal melatonin rise in patients with Huntington's disease.

Sleep disturbances are very prevalent in Huntington's disease (HD) patients and can substantially impair their quality of life. Accumulating evidence suggests considerable dysfunction of the hypothalamic suprachiasmatic nucleus (SCN), the biological clock, in both HD patients and transgenic mouse models of the disease. As melatonin has a major role in the regulation of sleep and other cyclical bodily activities and its synthesis is directly regulated by the SCN, we postulated that disturbed SCN function is likely to give rise to abnormal melatonin secretion in HD. Therefore, we compared 24 h melatonin secretion profiles between early stage HD patients and age-, sex- and body mass index-matched controls. Although mean diurnal melatonin levels were not different between the two groups (p = 0.691), the timing of the evening rise in melatonin levels was significantly delayed by more than 01:30 h in HD patients (p = 0.048). Moreover, diurnal melatonin levels strongly correlated with both motor (r = -0.70, p = 0.036) and functional impairment (r = +0.78, p = 0.013). These findings suggest a delayed sleep phase syndrome-like circadian rhythm disorder in early stage HD patients and suggest that melatonin levels may progressively decline with advancing disease.

Metabolic dysfunction and circadian rhythm abnormalities in adolescents with sleep disturbance.

BACKGROUND: Sleep disturbance attributable to circadian rhythm abnormalities frequently occurs in previously healthy children and adolescents who often complain of gastrointestinal discomfort after meals. METHODS: Glucose metabolism, autonomic function, and human clock gene expression in whole blood cells were investigated in 18 adolescent patients with circadian rhythm sleep disorder. RESULTS: Glucose tolerance was significantly lower in the patients than in normal controls: the mean sigma blood glucose level was significantly higher (P<0.05) and the insulinogenic index was significantly lower (P<0.05) in the patient group than in controls. Messenger ribonucleic acid level of hPer2 was significantly higher at 6:00 in the control subjects, but in only 3 of the 18 patients. Component analysis of cardiographic R-R interval revealed that high-frequency component peaks were suppressed significantly in the patient group compared to the controls (P<0.001). CONCLUSIONS: Metabolic and endocrine dysfunctions were identified in adolescents with sleep disturbance as decreased glucose tolerance and absence of human clock gene regulation in whole blood cells. Their brain dysfunction attributable to sleep disturbances might cause such peripheral autonomic imbalance and carbohydrate metabolic dysfunction.

Resting salivary and plasma cortisol in elite athletes following long-haul travel from Australia to Canada.

Salivary cortisol maybe a preferred method for monitoring the disruption of the body clock following travel across multiple time-zones due to ease of collection and the ability of salivary cortisol to reflect free cortisol. Salivary cortisol concentrations are approximately 5% of plasma cortisol concentrations. Whether the ratio of salivary to plasma cortisol is influenced by travel across time-zones in athletes is not well known. Early morning (8a.m.) resting salivary and plasma cortisol were measured in five Australian skeleton athletes (4F; 1M) on six mornings over 11 days following international travel from Australia to Canada (eight time-zones). The purpose of this study was to establish whether international travel affected both plasma and salivary cortisol by the same magnitude and for the same duration in this unique athletic population. Plasma cortisol was suppressed on Day-1 and Day-2 ( approximately 58% and approximately 67% of baseline, respectively), but average values were similar to baseline by Day-4. Salivary cortisol was noticeably suppressed on Day-1 and slightly suppressed on Day-2 and Day-4 but similar to baseline by Day-7. Saliva cortisol tended to be approximately 4% of plasma cortisol at baseline but decreased to approximately 2% on Day-2 and approximately 3.5% on Day-2 and Day-4. These findings document that the relationship between salivary and plasma cortisol can change following international travel and suggest that the extent of the disturbance in cortisol concentrations after crossing multiple time-zones may differ between plasma and saliva samples.