Effects of Acute Caffeine Intake on Insulin-Like Growth Factor-1 Responses to Total Sleep Deprivation: Interactions with COMT Polymorphism - A Randomized, Crossover Study.

INTRODUCTION: Genes encoding catechol-O-methyl-transferase (COMT) and adenosine A2A receptor (ADORA2A) have been shown to influence cognitive performances and responses to caffeine intake during prolonged wakefulness. The rs4680 single-nucleotide polymorphism (SNP) of COMT differentiates on memory score and circulating levels of the neurotrophic factor IGF-1. This study aimed to determine the kinetics of IGF-1, testosterone, and cortisol concentrations during prolonged wakefulness under caffeine or placebo intake in 37 healthy participants, and to analyze whether the responses are dependent on COMT rs4680 or ADORA2A rs5751876 SNPs. METHODS: In caffeine (2.5 mg/kg, twice over 24 h) or placebo-controlled condition, blood sampling was performed at 1 h (08:00, baseline), 11 h, 13 h, 25 h (08:00 next day), 35 h, and 37 h of prolonged wakefulness, and at 08:00 after one night of recovery sleep, to assess hormonal concentrations. Genotyping was performed on blood cells. RESULTS: Results indicated a significant increase in IGF-1 levels after 25, 35, and 37 h of prolonged wakefulness in the placebo condition, in subjects carrying the homozygous COMT A/A genotype only (expressed in absolute values [±SEM]: 118 ± 8, 121 ± 10, and 121 ± 10 vs. 105 ± 7 ng/mL for A/A, 127 ± 11, 128 ± 12, and 129 ± 13 vs. 120 ± 11 ng/mL for G/G, and 106 ± 9, 110 ± 10, and 106 ± 10 vs. 101 ± 8 ng/mL for G/A, after 25, 35, and 37 h of wakefulness versus 1 h; p < 0.05, condition X time X SNP). Acute caffeine intake exerted a COMT genotype-dependent reducing effect on IGF-1 kinetic response (104 ± 26, 107 ± 27, and 106 ± 26 vs. 100 ± 25 ng/mL for A/A genotype, at 25, 35, and 37 h of wakefulness vs. 1 h; p < 0.05 condition X time X SNP), plus on resting levels after overnight recovery (102 ± 5 vs. 113 ± 6 ng/mL) (p < 0.05, condition X SNP). Testosterone and cortisol concentrations decreased during wakefulness, and caffeine alleviated the testosterone reduction, unrelated to the COMT polymorphism. No significant main effect of the ADORA2A SNP was shown regardless of hormonal responses. CONCLUSION: Our results indicated that the COMT polymorphism interaction is important in determining the IGF-1 neurotrophic response to sleep deprivation with caffeine intake (NCT03859882).

Relationship between genetic polymorphisms of cytokines and self-reported sleep complaints and habitual caffeine consumption.

Pro-inflammatory cytokines are involved in sleep-wake regulation and are associated with caffeine consumption. This is a cross-sectional study in 1023 active French workers investigating associations between self-reported sleep complaints (>3months) and total sleep time (TST) with nine single-nucleotide-polymorphisms (SNPs) including pro-inflammatory cytokines, according to caffeine consumption. Participants were characterized as low, moderate and high (0-50, 51-300, and >300 mg/day) caffeine consumers. After adjusting the odd ratios (OR) for age, gender, and smoking, the risk of sleep complaints was higher in subjects with genetic mutations in tumor necrosis factor alpha (TNF-α, rs 1800629) (ORa [95%CI] = 1.43 [1.07-1.92] for both G/A and A/A aggregate genotypes) or interleukin-1 beta (IL-1ß, rs1143627) (ORa = 1.61 [1.08-2.44] for homozygous A/A genotype), and the risk was higher when subjects carry the mutations in TNF-α plus IL-1ß regardless of caffeine consumption. When stratified with caffeine consumption, the risk of sleep complaints was higher in TNF-α A allele carriers in high caffeine consumers, and in homozygous A/A genotype of IL-1ß in moderate and high consumers. None of the nine SNPs influence TST, with the exception of the mutation on CYP1A2 and only when stratified with caffeine consumption. Our results also indicated more caffeine side-effects when carrying mutation on IL1ß. This study showed that polymorphisms in TNF-α and/or IL-1ß influenced sleep complaints but did not influence total sleep time. This suggests that management of sleep complaints, which can be addressed by clinical interventions, should consider the influence of the genetic profile of pro-inflammatory cytokines.

Immune disruptions and night shift work in hospital healthcare professionals: The intricate effects of social jet-lag and sleep debt.

Objectives: We aimed to examine the effects of circadian and sleep rhythm disruptions on immune biomarkers among hospital healthcare professionals working night shifts and rotating day shifts. Methods: Hospital nurses working either as permanent night shifters (n=95) or as day shifters rotating between morning and afternoon shifts (n=96) kept a daily diary on their sleep and work schedules over a full working week. Blood samples were collected at the beginning and end of the last shift during the week, and participants were categorized into three groups based on work shift: morning shift (39 day shifters sampled at 7:00 and 14:00), afternoon shift (57 day shifters sampled at 14:00 and 21:00), and night shift (95 night shifters sampled at 21:00 and 7:00). Circulating blood counts in immune cells, interleukin-6 and C-reactive protein concentrations as well as total sleep time per 24 hours during work days (TST24w) and free days (TST24f), sleep debt (TST24f - TST24w) and social jet-lag (a behavioral proxy of circadian misalignment) were assessed. Results: Compared with day shifters, night shifters had shorter sleep duration (TST24w=5.4 ± 1.4h), greater sleep debt (3.2 ± 1.4 h) and social jet-lag (6.7 ± 2.4 h). Variations of immune biomarkers concentrations were consistent with the expected diurnal variations among day shifters (i.e., low level in the morning, increase during the day, peak value in the evening). By contrast, in night shifters, blood concentrations of total lymphocytes, T-helper cells, cytotoxic T-cells, memory B-cells and interleukin-6 were lower at 21:00, increased during the night, and reached higher values at 7:00. Multivariate analyses ruled out significant impact of TST24w, sleep debt, and social jet-lag on immune biomarkers concentrations among day shifters. In contrast, among night shifters, multivariate analyses indicated a combined effect of total sleep time (TST24w), sleep debt and social jet-lag for total lymphocytes and T-helper cells but only a social jet-lag effect for interleukin-6 and a single total sleep time effect for neutrophil and B-Cells. Conclusions: Altogether, our results point to intricate response patterns of immune rhythms to circadian misalignment and sleep debt in night shifters. Specifically, these altered pattern expressions of immune cells may increase vulnerability to infections and reduce vaccination efficiency in night workers.

Effects of Caffeine Intake on Cognitive Performance Related to Total Sleep Deprivation and Time on Task: A Randomized Cross-Over Double-Blind Study.

Introduction: It is widely admitted that both total sleep deprivation (TSD) and extended task engagement (Time-On-Task, TOT) induce a cognitive fatigue state in healthy subjects. Even if EEG theta activity and adenosine both increase with cognitive fatigue, it remains unclear if these modifications are common mechanisms for both sustained attention and executive processes. Methods: We performed a double-blind counter-balanced (placebo (PCBO) and caffeine (CAF) - 2×2.5 mg/kg/24 h)) study on 24 healthy subjects (33.7 ± 5.9 y). Subjects participated in an experimental protocol including an habituation/training day followed by a baseline day (D0 and D1) and a total sleep deprivation (TSD) day beginning on D1 at 23:00 until D2 at 21:00. Subjects performed the psychomotor vigilance test (PVT) assessing sustained attention, followed by the executive Go-NoGo inhibition task and the 2-NBack working memory task at 09:15 on D1 and D2. Results: We showed differential contributions of TSD and TOT on deficits in sustained attention and both executive processes. An alleviating effect of caffeine intake is only observed on sustained attention deficits related to TSD and not at all on TOT effect. The caffeine dose slows down the triggering of sustained attention deficits related to TOT effect. Discussion: These results suggest that sustained attention deficits induced by TSD rely on the adenosinergic mechanism whereas TOT effect observed for both sustained attention and executive would not.

Genetics and Cognitive Vulnerability to Sleep Deprivation in Healthy Subjects: Interaction of ADORA2A, TNF-α and COMT Polymorphisms.

Several genetic polymorphisms differentiate between healthy individuals who are more cognitively vulnerable or resistant during total sleep deprivation (TSD). Common metrics of cognitive functioning for classifying vulnerable and resilient individuals include the Psychomotor Vigilance Test (PVT), Go/noGo executive inhibition task, and subjective daytime sleepiness. We evaluated the influence of 14 single-nucleotide polymorphisms (SNPs) on cognitive responses during total sleep deprivation (continuous wakefulness for 38 h) in 47 healthy subjects (age 37.0 ± 1.1 years). SNPs selected after a literature review included SNPs of the adenosine-A2A receptor gene (including the most studied rs5751876), pro-inflammatory cytokines (TNF-α, IL1-ß, IL-6), catechol-O-methyl-transferase (COMT), and PER3. Subjects performed a psychomotor vigilance test (PVT) and a Go/noGo-inhibition task, and completed the Karolinska Sleepiness Scale (KSS) every 6 h during TSD. For PVT lapses (reaction time >500 ms), an interaction between SNP and SDT (p < 0.05) was observed for ADORA2A (rs5751862 and rs2236624) and TNF-α (rs1800629). During TSD, carriers of the A allele for ADORA2A (rs5751862) and TNF-α were significantly more impaired for cognitive responses than their respective ancestral G/G genotypes. Carriers of the ancestral G/G genotype of ADORA2A rs5751862 were found to be very similar to the most resilient subjects for PVT lapses and Go/noGo commission errors. Carriers of the ancestral G/G genotype of COMT were close to the most vulnerable subjects. ADORA2A (rs5751862) was significantly associated with COMT (rs4680) (p = 0.001). In conclusion, we show that genetic polymorphisms in ADORA2A (rs5751862), TNF-α (rs1800629), and COMT (rs4680) are involved in creating profiles of high vulnerability or high resilience to sleep deprivation. (NCT03859882).

Genetic Determinants of Neurobehavioral Responses to Caffeine Administration during Sleep Deprivation: A Randomized, Cross Over Study (NCT03859882).

This study investigated whether four single nucleotide polymorphisms (SNPs) moderated caffeine effects on vigilance and performance in a double-blind and crossover total sleep deprivation (TSD) protocol in 37 subjects. In caffeine (2 × 2.5 mg/kg/24 h) or placebo-controlled condition, subjects performed a psychomotor vigilance test (PVT) and reported sleepiness every six hours (Karolinska sleepiness scale (KSS)) during TSD. EEG was also analyzed during the 09:15 PVT. Carriers of the TNF-α SNP A allele appear to be more sensitive than homozygote G/G genotype to an attenuating effect of caffeine on PVT lapses during sleep deprivation only because they seem more degraded, but they do not perform better as a result. The A allele carriers of COMT were also more degraded and sensitive to caffeine than G/G genotype after 20 h of sleep deprivation, but not after 26 and 32 h. Regarding PVT reaction time, ADORA2A influences the TSD effect but not caffeine, and PER3 modulates only the caffeine effect. Higher EEG theta activity related to sleep deprivation was observed in mutated TNF-α, PER3, and COMT carriers, in the placebo condition particularly. In conclusion, there are genetic influences on neurobehavioral impairments related to TSD that appear to be attenuated by caffeine administration. (NCT03859882).

The Impact of Genetic Variations in ADORA2A in the Association between Caffeine Consumption and Sleep.

ADORA2A has been shown to be responsible for the wakefulness-promoting effect of caffeine and the 1976T>C genotype (SNP rs5751876, formerly 1083T>C) to contribute to individual sensitivity to caffeine effects on sleep. We investigate the association between six single nucleotide polymorphisms (SNP) from ADORA2A and self-reported sleep characteristics and caffeine consumption in 1023 active workers of European ancestry aged 18-60 years. Three groups of caffeine consumers were delineated: low (0-50 mg/day, less than one expresso per day), moderate (51-300 mg/day), and high (>300 mg/day). We found that at caffeine levels higher than 300 mg/day, total sleep time (TST) decreased (F = 13.9, p < 0.01), with an increase of insomnia (ORa [95%CI] = 1.5 [1.1-1.9]) and sleep complaints (ORa [95%CI] = 1.9 [1.1-3.3]), whatever the ADORA2A polymorphism. Odds ratios were adjusted (ORa) for sex, age, and tobacco. However, in low caffeine consumers, lower TST was observed in the T allele compared to homozygote rs5751876 and rs3761422 C carriers. Conversely, higher TST was observed in rs2298383 T allele compared to C and in rs4822492G allele compared to the homozygote C (p < 0.05). These 4 SNPs are in strong linkage disequilibrium. Haplotype analysis confirmed the influence of multiple ADORA2a SNPs on TST. In addition, the rs2298383 T and rs4822492 G alleles were associated with higher risk of sleep complaints (Ora = 1.9 [1.2-3.1] and Ora = 1.5 [1.1-2.1]) and insomnia (Ora = 1.5 [1.3-2.5] and Ora = 1.9 [1.3-3.2). The rs5751876 T allele was associated with a decreased risk of sleep complaints (Ora = 0.7 [0.3-0.9]) and insomnia (Ora = 0.5 [0.3-0.9]). Our results identified ADORA2A polymorphism influences in the less-than-300-mg-per-day caffeine consumers. This opens perspectives on the diagnosis and pharmacology of sleep complaints and caffeine chronic consumption.

Changes of Cerebral and/or Peripheral Adenosine A1 Receptor and IGF-I Concentrations under Extended Sleep Duration in Rats.

Extended sleep improves sustained attention and reduces sleep pressure in humans. Downregulation of adenosine A1 receptor (A1R) and modulation of the neurotrophic factor insulin growth factor-1 (IGF-I) in brain structures controlling attentional capacities could be involved. In the frontal cortex and hippocampus of rats, we measured adenosine A1R and IGF-I protein concentrations after photoperiod-induced sleep extension. Two groups of twelve rats were adapted over 14 days to a habitual (CON) 12:12 light-dark (LD) schedule and an extended (EXT) 16:8 LD schedule. IGF-I content was also measured in plasma, liver, and skeletal muscle. In EXT, compared to CON rats, A1R content in the frontal cortex was significantly lower (p < 0.05), while IGF-I content was higher (p < 0.001), and no significant change was observed in the hippocampus. IGF-I content in plasma and muscle was higher (p < 0.001 and p < 0.01), while it was lower in liver (p < 0.001). The absolute weight and weight gain were higher in EXT rats (p < 0.01). These data suggest that 14 days under a 16:8 LD photoperiod respectively down- and upregulated cortical A1R and IGF-I levels. This photoperiod induced an anabolic profile with increased weight gain and circulating and muscular IGF-I levels. An extension of sleep duration might favor cerebral and peripheral anabolism, which may help attentional and physical capacities.

Leukocyte Expression of Type 1 and Type 2 Purinergic Receptors and Pro-Inflammatory Cytokines during Total Sleep Deprivation and/or Sleep Extension in Healthy Subjects.

The purinergic type P1 (adenosine A1 and A2A) receptors and the type P2 (X7) receptor have been suggested to mediate physiological effects of adenosine and adenosine triphosphate on sleep. We aimed to determine gene expression of A1R (receptor), A2AR, and P2RX7 in leukocytes of healthy subjects during total sleep deprivation followed by sleep recovery. Expression of the pro-inflammatory cytokines IL-1ß and TNF-α were also determined as they have been characterized as sleep regulatory substances, via P2RX7 activation. Blood sampling was performed on 14 young men (aged 31.9 ± 3.9) at baseline (B), after 24 h of sleep deprivation (24 h-SD), and after one night of sleep recovery (R). We compared gene expression levels after six nights of habitual (22.30-07.00) or extended (21.00-07.00) bedtimes. Using quantitative real-time PCR, the amount of mRNA for A1R, A2AR, P2RX7, TNF-α, and IL-1ß was analyzed. After 24 h-SD compared to B, whatever prior sleep condition, a significant increase of A2AR expression was observed that returned to basal level after sleep recovery [day main effect, F(2, 26) = 10.8, p < 0.001]. In both sleep condition, a day main effect on P2RX7 mRNA was observed [F(2, 26) = 6.7, p = 0.005] with significant increases after R compared with 24 h-SD. TNF-α and IL-1ß expressions were not significantly altered. Before 24 h-SD (baseline), the A2AR expression was negatively correlated with the latency of stage 3 sleep during the previous night, while that of the A1R positively. This was not observed after sleep recovery following 24 h-SD. This is the first study showing increased A2AR and not A1 gene expression after 24 h-SD in leukocytes of healthy subjects, and this even if bedtime was initially increased by 1.5 h per night for six nights. In conclusion, prolonged wakefulness induced an up-regulation of the A2A receptor gene expression in leukocytes from healthy subjects. Significant correlations between baseline expression of A1 and A2A receptors in peripheral cells and stage 3 sleep suggested their involvement in mediating the effects of adenosine on sleep.

Napping reverses the salivary interleukin-6 and urinary norepinephrine changes induced by sleep restriction.

CONTEXT: Neuroendocrine and immune stresses imposed by chronic sleep restriction are known to be involved in the harmful cardiovascular effects associated with poor sleep. OBJECTIVES: Despite a well-known beneficial effect of napping on alertness, its effects on neuroendocrine stress and immune responses after sleep restriction are largely unknown. DESIGN: This study was a strictly controlled (sleep-wake status, light environment, caloric intake), crossover, randomized design in continuously polysomnography-monitored subjects. SETTING: The study was conducted in a laboratory-based study. PARTICIPANTS: The subjects were 11 healthy young men. INTERVENTION: We investigated the effects on neuroendocrine and immune biomarkers of a night of sleep restricted to 2 h followed by a day without naps or with 30 minute morning and afternoon naps, both conditions followed by an ad libitum recovery night starting at 20:00. MAIN OUTCOME MEASURES: Salivary interleukin-6 and urinary catecholamines were assessed throughout the daytime study periods. RESULTS: The increase in norepinephrine values seen at the end of the afternoon after the sleep-restricted night was not present when the subjects had the opportunity to take naps. Interleukin-6 changes observed after sleep deprivation were also normalized after napping. During the recovery day in the no-nap condition, there were increased levels of afternoon epinephrine and dopamine, which was not the case in the nap condition. A recovery night after napping was associated with a reduced amount of slow-wave sleep compared to after the no-nap condition. CONCLUSIONS: Our data suggest that napping has stress-releasing and immune effects. Napping could be easily applied in real settings as a countermeasure to the detrimental health consequences of sleep debt.

Effect of acute sleep deprivation and recovery on Insulin-like Growth Factor-I responses and inflammatory gene expression in healthy men.

Acute sleep deprivation in humans has been found to increase inflammatory markers and signaling pathways in the periphery through a possible Toll-like receptor 4 (TLR-4). In addition, short duration sleep has been associated with low circulating total Insulin-like Growth Factor-I (IGF-I) concentrations. We aimed to determine whether a total sleep deprivation (TSD) protocol with recovery altered whole-blood gene expression of the proinflammatory cytokines TNF-α and IL-6, as well as TLR-4 expression, and to examine the relationship with circulating concentrations of the IGF-I system. Twelve healthy men participated in a five-day TSD (two control nights followed by one night of sleep deprivation and one night of recovery). Blood was sampled at 0800, before and after sleep deprivation (D2 and D4), and after recovery (D5). It is shown that 25 h of sleep deprivation (D4) induced significant increases in mRNA levels of TNF-α and its soluble receptor R1 (P<0.01 respectively), as well as TLR-4 (P<0.05), while IL-6 mRNA levels remained unchanged. Circulating concentrations of free IGF-I were decreased at D4 (P<0.001). One night of recovery was sufficient to restore basal expression levels for TNF-α, sTNF-R1, TLR-4 and circulating IGF-I. Changes in TLR-4 mRNA levels during the protocol correlated positively with those of TNF-α and sTNF-R1 (r=0.393 and r=0.490 respectively), and negatively with circulating free IGF-I (r=-0.494). In conclusion, 25 h of sleep deprivation in healthy subjects is sufficient to induce transient and reversible genomic expression of the pro-inflammatory cytokine TNF-α and its R1 receptor, and its mediator TLR-4, with a possible link to IGF-I axis inhibition.

Effects of Ramadan fasting on physical performance and metabolic, hormonal, and inflammatory parameters in middle-distance runners.

The Ramadan fasting (RF) period is associated with changes in sleep habits and increased sleepiness, which may affect physical performance in athletes, and may induce metabolic, hormonal, and inflammatory disturbances. In 8 middle-distance athletes (25.0 +/- 1.3 years), a maximal aerobic velocity (MAV) test was performed 5 days before RF (day -5), and on days 7 and 21 of RF. The same days, saliva samples were collected to determine cortisol and testosterone concentrations before and after the MAV test. Blood samples were collected before RF (P1), at the end of RF (P2), and 1 week post RF (P3). Plasma levels of interleukin (IL)-6, a mediator of sleepiness and energy availability, were determined. We also evaluated changes in metabolic and hormonal parameters, mood state, and nutritional and sleep profiles. During RF, mean body mass and body fat did not statistically change. Compared with day -5, MAV values decreased at days 7 and 21 (p < 0.05, respectively), while testosterone/cortisol ratio values did not change significantly. Nocturnal sleep time and energy intake were lower at day 21 than before RF (day 0/P1) (p < 0.05). At the end of RF (day 31), the fatigue score on the Profile of Mood States questionnaire was increased (p < 0.001). For P2 vs. P1, IL-6 was increased (1.19 +/- 0.25 vs. 0.51 +/- 0.13 pg.mL-1; p < 0.05), melatonin levels were decreased (p < 0.05), and adrenalin and noradrenalin were increased (p < 0.01 and p < 0.001, respectively). At 7 days post RF, all parameters recovered to pre-RF values. In conclusion, RF is accompanied by significant metabolic, hormonal, and inflammatory changes. Sleep disturbances, energy deficiency, and fatigue during RF may decrease physical performance in Muslim athletes who maintain training. Reduction of work load and (or) daytime napping may represent adequate strategies to counteract RF effects for Muslim athletes.

Effects of physical training on IL-1beta, IL-6 and IL-1ra concentrations in various brain areas of the rat.

There is increasing evidence that voluntary physical activity and exercise training have beneficial effects on brain function by facilitating neurovegetative, neuroadaptative and neuroprotective processes. Cytokines are chronically expressed at elevated levels within the CNS in many neurological disorders and may contribute to the histopathological, pathophysiological, and cognitive deficits associated with such disorders. In the present study, we examined the influence of seven weeks of physical training on IL-1b, IL-6 and IL-1ra concentrations in hypothalamus, pituitary, hippocampus, cerebellum and frontal cortex in rats. We determined circulating concentrations of cytokines, corticosterone, prolactin and leptin. Two groups of 10 rats were investigated: one group (trained rats) was progressively trained (5 days/week); the other group (sedentary rats) was used as a sedentary group. The training program induced a decrease of (i) IL-1b concentration in the hippocampus (0.7 +/- 0.16 versus 0.99 +/- 0.14 pg/mg protein; p < 0.05), (ii) IL-6 concentration in the cerebellum (10.7 +/- 1.00 in trained rats versus 14.8 +/- 1.34 pg/mg protein in sedentary rats; p < 0.05), (iii) IL-1ra concentration in the pituitary (245 +/- 14.31 versus 328 +/- 17.73 pg/mg protein; p < 0.01). We also found positive correlations between (i) serum prolactin and the concentration of IL-6 in the cerebellum, (ii) serum leptin and the concentration of IL-1ra in the pituitary. There was no effect of physical training on IL-1b, IL-6, and IL-1ra serum levels. These findings suggest that the decrease in particular pro-inflammatory, central cytokines such as IL-1b and IL-6 induced by the training program may play a role in the positive effects of regular physical activity on the central nervous system.

Effects of combined stress during intense training on cellular immunity, hormones and respiratory infections.

OBJECTIVES: This study was designed to determine immune and hormonal changes and their relationship with the incidence of upper respiratory tract infections (URTIs) during an extremely stressful military training (3 weeks of physical conditioning followed by a 5-day combat course with energy restriction, sleep deprivation and psychological stress). METHODS: Blood samples were collected from 21 cadets (21 +/- 2 years old) before training and after the combat course for analysis of leukocyte and lymphocyte subpopulations, serum cytokines [interleukin-6 (IL-6), IL-1beta and IL-10], and hormones [catecholamines, cortisol, leptin, total insulin-like growth factor I (IGF-I), prolactin, dehydroepiandrosterone sulfate (DHEAS) and testosterone]. Symptoms of URTI were recorded from health logs and medical examinations during training. RESULTS: After the combat course, total leukocyte and neutrophil counts were significantly increased while total lymphocytes were unchanged. In lymphocyte subsets, NK cells were reduced (p < 0.01), while CD4+ and CD19+ (B) cells were increased. Levels of IL-6 were increased (p < 0.01), while those of IL-1beta and IL-10 were unchanged. Norepinephrine and dopamine levels were increased, while those of cortisol were reduced. Levels of leptin, testosterone, prolactin and total IGF-I were reduced, while those of DHEAS were increased. The incidence of URTI increased during the training (chi(2) = 53.48, p < 0.05). After training data analysis showed a significant correlation between URTIs and NK cells (p = 0.0023). Training-induced changes in immune and hormonal parameters were correlated. CONCLUSIONS: Blood NK cell levels are related to increased respiratory infections during physical training in a multistressor environment. The training-induced decreases in immunostimulatory hormone levels may have triggered immunosuppression.

Immune and hormonal changes following intense military training.

This study was designed to determine whether the immune and hormonal systems were affected by a 5-day military course following 3 weeks of combat training in a population of 26 male soldiers (mean age, 21 +/- 2 years). The combination of continuous heavy physical activity and sleep deprivation led to energy deficiency. At the beginning of the training program and immediately after the combat course, saliva samples were assayed for secretory immunoglobulin A and plasma samples were assayed for interleukin-6, dehydroepiandrosterone sulfate, prolactin, catecholamines, glucocorticoids, and testosterone. Secretory immunoglobulin A was lower and circulating interleukin-6 was increased by the end of the course, which was attributed to sympathoadrenergic stimulation. Dehydroepiandrosterone sulfate, prolactin, and testosterone levels fell significantly. These results suggest that prolonged and repeated exercise such as that encountered in a military training program induces immune impairment via a decrease in mucosal immunity and a release of interleukin-6 into the circulation. The impaired secretion of dehydroepiandrosterone sulfate and prolactin, two immunomodulatory hormones, was thought to be a response to the chronic stressors. Lowered testosterone reflects a general decrease in steroid synthesis as a consequence of the physical and psychological strain.