Sex differences in iron status during military training: a prospective cohort study of longitudinal changes and associations with endurance performance and musculoskeletal outcomes.

This study investigated sex differences in Fe status, and associations between Fe status and endurance and musculoskeletal outcomes, in military training. In total, 2277 British Army trainees (581 women) participated. Fe markers and endurance performance (2·4 km run) were measured at the start (week 1) and end (week 13) of training. Whole-body areal body mineral density (aBMD) and markers of bone metabolism were measured at week 1. Injuries during training were recorded. Training decreased Hb in men and women (mean change (-0·1 (95 % CI -0·2, -0·0) and -0·7 (95 % CI -0·9, -0·6) g/dl, both P < 0·001) but more so in women (P < 0·001). Ferritin decreased in men and women (-27 (95 % CI -28, -23) and -5 (95 % CI -8, -1) µg/l, both P ≤ 0·001) but more so in men (P < 0·001). Soluble transferrin receptor increased in men and women (2·9 (95 % CI 2·3, 3·6) and 3·8 (95 % CI 2·7, 4·9) nmol/l, both P < 0·001), with no difference between sexes (P = 0·872). Erythrocyte distribution width increased in men (0·3 (95 % CI 0·2, 0·4)%, P < 0·001) but not in women (0·1 (95 % CI -0·1, 0·2)%, P = 0·956). Mean corpuscular volume decreased in men (-1·5 (95 % CI -1·8, -1·1) fL, P < 0·001) but not in women (0·4 (95 % CI -0·4, 1·3) fL, P = 0·087). Lower ferritin was associated with slower 2·4 km run time (P = 0·018), sustaining a lower limb overuse injury (P = 0·048), lower aBMD (P = 0·021) and higher beta C-telopeptide cross-links of type 1 collagen and procollagen type 1 N-terminal propeptide (both P < 0·001) controlling for sex. Improving Fe stores before training may protect Hb in women and improve endurance and protect against injury.

A comparison of medium-term heat acclimation by post-exercise hot water immersion or exercise in the heat: adaptations, overreaching, and thyroid hormones.

This research compared thermal and perceptual adaptations, endurance capacity, and overreaching markers in men after 3, 6, and 12 days of post-exercise hot water immersion (HWI) or exercise heat acclimation (EHA) with a temperate exercise control (CON), and examined thyroid hormones as a mechanism for the reduction in resting and exercising core temperature (Tre) after HWI. HWI involved a treadmill run at 65% V̇o2peak at 19°C followed by a 40°C bath. EHA and CON involved a work-matched treadmill run at 65% V̇o2peak at 33°C or 19°C, respectively. Compared with CON, resting mean body temperature (Tb), resting and end-exercise Tre, Tre at sweating onset, thermal sensation, and perceived exertion were lower and whole-body sweat rate (WBSR) was higher after 12 days of HWI (all P ≤ 0.049, resting Tb: CON -0.11 ± 0.15°C, HWI -0.41 ± 0.15°C). Moreover, resting Tb and Tre at sweating onset were lower after HWI than EHA (P ≤ 0.015, resting Tb: EHA -0.14 ± 0.14°C). No differences were identified between EHA and CON (P ≥ 0.157) except WBSR that was greater after EHA (P = 0.013). No differences were observed between interventions for endurance capacity or overreaching markers (mood, sleep, Stroop, P ≥ 0.190). Thermal adaptations observed after HWI were not related to changes in thyroid hormone concentrations (P ≥ 0.086). In conclusion, 12 days of post-exercise hot water immersion conferred more complete heat acclimation than exercise heat acclimation without increasing overreaching risk, and changes in thyroid hormones are not related to thermal adaptations after post-exercise hot water immersion.

Supplemental Protein and a Multinutrient Beverage Speed Wound Healing after Acute Sleep Restriction in Healthy Adults.

BACKGROUND: Physiologic and psychologic stress slow healing from experimental wounds by impairing immune function. OBJECTIVES: We aimed to determine whether supplemental protein and multinutrient supplementation improved wound healing markers after acute stress induced by acute sleep restriction. METHODS: In this single-blind, crossover study in generally healthy young adults (18 males/2 females; mean ± SD age: 19.7 ± 2.30 y), experimental wounds were created by removing the top layer of forearm blisters induced via suction after 48 h of 72-h sleep restriction (2-h nightly sleep), a protocol previously shown to delay wound healing. Skin barrier restoration (measured by transepidermal water loss) assessed wound healing ≤10 d postblistering, and local immune responses were evaluated by serial measurement of cytokine concentrations in fluid collected at wound sites for 48 h postblistering. Participants consumed controlled, isocaloric diets with either 0.900 g · kg-1 · d-1 protein plus placebo (PLA) or 1.50 g · kg-1 · d-1 protein plus multinutrient beverage [l-arginine: 20.0 g/d; l-glutamine: 30.0 g/d; omega-3 (n-3) fatty acids: 1.00 g/d; zinc sulfate: 24.0 mg/d; cholecalciferol: 800 IU/d; and vitamin C: 400 mg/d] (NUT) during sleep restriction and for 4 d afterwards. RESULTS: Skin barrier restoration (primary outcome) was shorter for NUT (median: 3.98 d; IQR: 1.17 d) than for PLA (median: 5.25 d; IQR: 1.05 d) (P = 0.001). Cytokines from wound fluid (secondary outcome) increased over time (main effect of time P ≤ 0.001), except IL-13 (P = 0.07); however, no effects of treatment were observed. CONCLUSIONS: Supplemental nutrition may promote wound healing after sleep restriction in healthy adults including military personnel, the latter of which also have a high incidence of wounds and infection.This trial was registered at clinicaltrials.gov as NCT03525184.

"Food First but Not Always Food Only": Recommendations for Using Dietary Supplements in Sport.

The term "food first" has been widely accepted as the preferred strategy within sport nutrition, although there is no agreed definition of this and often limited consideration of the implications. We propose that food first should mean "where practically possible, nutrient provision should come from whole foods and drinks rather than from isolated food components or dietary supplements." There are many reasons to commend a food first strategy, including the risk of supplement contamination resulting in anti-doping violations. However, a few supplements can enhance health and/or performance, and therefore a food only approach could be inappropriate. We propose six reasons why a food only approach may not always be optimal for athletes: (a) some nutrients are difficult to obtain in sufficient quantities in the diet, or may require excessive energy intake and/or consumption of other nutrients; (b) some nutrients are abundant only in foods athletes do not eat/like; (c) the nutrient content of some foods with established ergogenic benefits is highly variable; (d) concentrated doses of some nutrients are required to correct deficiencies and/or promote immune tolerance; (e) some foods may be difficult to consume immediately before, during or immediately after exercise; and (f) tested supplements could help where there are concerns about food hygiene or contamination. In these situations, it is acceptable for the athlete to consider sports supplements providing that a comprehensive risk minimization strategy is implemented. As a consequence, it is important to stress that the correct terminology should be "food first but not always food only."

Illness Incidence, Psychological Characteristics, and Sleep in Dogsled Drivers During the Iditarod Trail Sled Dog Race.

INTRODUCTION: Every March, dogsled drivers (mushers) compete in a 1569-km race across Alaska, involving physical exertion, mental exertion, and sleep deprivation for up to 2 wk. These factors may increase mushers' vulnerability to illness, making them a relevant study population for acute infection risk factors. Specifically, the influence of psychological factors on illness risk during prolonged physical exertion has rarely been investigated. The aim of this study was to examine the relationship between psychological characteristics, sleep deprivation, and illness incidence in Iditarod mushers. METHODS: Fourteen mushers completed 4 psychological instruments to assess state and trait anxiety, resilience and perceived stress, and self-reported upper respiratory symptoms (URS) in the month before the race. Mushers self-reported sleep duration and URS during the race. RESULTS: State and trait anxiety, resilience, and perceived stress did not differ between mushers with and without pre- and in-race URS (P>0.05). However, all mushers who reported in-race URS had reported URS ≤9 d before the race, and the onset of symptoms during the race typically occurred shortly after a rest period. Sleep duration was higher in mushers who reported in-race URS, both before (4.9±0.3 h, P=0.016) and during illness (5.9±1.3 h, P=0.006), vs mushers without in-race URS (3.4±0.8 h). CONCLUSIONS: This study highlights recent illness, rest periods, and greater sleep requirements as potential risk factors for URS onset during a multiday endurance challenge, whereas psychological factors were not associated with URS.

Vitamin D and the hepatitis B vaccine response: a prospective cohort study and a randomized, placebo-controlled oral vitamin D3 and simulated sunlight supplementation trial in healthy adults.

PURPOSE: To determine serum 25(OH)D and 1,25(OH)2D relationship with hepatitis B vaccination (study 1). Then, to investigate the effects on hepatitis B vaccination of achieving vitamin D sufficiency (serum 25(OH)D ≥ 50 nmol/L) by a unique comparison of simulated sunlight and oral vitamin D3 supplementation in wintertime (study 2). METHODS: Study 1 involved 447 adults. In study 2, 3 days after the initial hepatitis B vaccination, 119 men received either placebo, simulated sunlight (1.3 × standard-erythema dose, 3 × /week for 4 weeks and then 1 × /week for 8 weeks) or oral vitamin D3 (1000 IU/day for 4 weeks and 400 IU/day for 8 weeks). We measured hepatitis B vaccination efficacy as percentage of responders with anti-hepatitis B surface antigen immunoglobulin G ≥ 10 mIU/mL. RESULTS: In study 1, vaccine response was poorer in persons with low vitamin D status (25(OH)D ≤ 40 vs 41-71 nmol/L mean difference [95% confidence interval] - 15% [- 26, - 3%]; 1,25(OH)2D ≤ 120 vs ≥ 157 pmol/L - 12% [- 24%, - 1%]). Vaccine response was also poorer in winter than summer (- 18% [- 31%, - 3%]), when serum 25(OH)D and 1,25(OH)2D were at seasonal nadirs, and 81% of persons had serum 25(OH)D < 50 nmol/L. In study 2, vitamin D supplementation strategies were similarly effective in achieving vitamin D sufficiency from the winter vitamin D nadir in almost all (~ 95%); however, the supplementation beginning 3 days after the initial vaccination did not effect the vaccine response (vitamin D vs placebo 4% [- 21%, 14%]). CONCLUSION: Low vitamin D status at initial vaccination was associated with poorer hepatitis B vaccine response (study 1); however, vitamin D supplementation commencing 3 days after vaccination (study 2) did not influence the vaccination response. CLINICAL TRIAL REGISTRY NUMBER: Study 1 NCT02416895; https://clinicaltrials.gov/ct2/show/study/NCT02416895 ; Study 2 NCT03132103; https://clinicaltrials.gov/ct2/show/NCT03132103 .

Can exercise affect immune function to increase susceptibility to infection?

Multiple studies in humans and animals have demonstrated the profound impact that exercise can have on the immune system. There is a general consensus that regular bouts of short-lasting (i.e. up to 45 minutes) moderate intensity exercise is beneficial for host immune defense, particularly in older adults and people with chronic diseases. In contrast, infection burden is reported to be high among high performance athletes and second only to injury for the number of training days lost during preparation for major sporting events. This has shaped the common view that arduous exercise (i.e. those activities practiced by high performance athletes/ military personnel that greatly exceed recommended physical activity guidelines) can suppress immunity and increase infection risk. However, the idea that exercise per se can suppress immunity and increase infection risk independently of the many other factors (e.g. anxiety, sleep disruption, travel, exposure, nutritional deficits, environmental extremes, etc.) experienced by these populations has recently been challenged. The purpose of this debate article was to solicit opposing arguments centered around this fundamental question in the exercise immunology field: can exercise affect immune function to increase susceptibility to infection. Issues that were contested between the debating groups include: (i) whether or not athletes are more susceptible to infection (mainly of the upper respiratory tract) than the general population; (ii) whether exercise per se is capable of altering immunity to increase infection risk independently of the multiple factors that activate shared immune pathways and are unique to the study populations involved; (iii) the usefulness of certain biomarkers and the interpretation of in vitro and in vivo data to monitor immune health in those who perform arduous exercise; and (iv) the quality of scientific evidence that has been used to substantiate claims for and against the potential negative effects of arduous exercise on immunity and infection risk. A key point of agreement between the groups is that infection susceptibility has a multifactorial underpinning. An issue that remains to be resolved is whether exercise per se is a causative factor of increased infection risk in athletes. This article should provide impetus for more empirical research to unravel the complex questions that surround this contentious issue in the field of exercise immunology.

Sleep and the athlete: narrative review and 2021 expert consensus recommendations.

Elite athletes are particularly susceptible to sleep inadequacies, characterised by habitual short sleep (<7 hours/night) and poor sleep quality (eg, sleep fragmentation). Athletic performance is reduced by a night or more without sleep, but the influence on performance of partial sleep restriction over 1-3 nights, a more real-world scenario, remains unclear. Studies investigating sleep in athletes often suffer from inadequate experimental control, a lack of females and questions concerning the validity of the chosen sleep assessment tools. Research only scratches the surface on how sleep influences athlete health. Studies in the wider population show that habitually sleeping <7 hours/night increases susceptibility to respiratory infection. Fortunately, much is known about the salient risk factors for sleep inadequacy in athletes, enabling targeted interventions. For example, athlete sleep is influenced by sport-specific factors (relating to training, travel and competition) and non-sport factors (eg, female gender, stress and anxiety). This expert consensus culminates with a sleep toolbox for practitioners (eg, covering sleep education and screening) to mitigate these risk factors and optimise athlete sleep. A one-size-fits-all approach to athlete sleep recommendations (eg, 7-9 hours/night) is unlikely ideal for health and performance. We recommend an individualised approach that should consider the athlete's perceived sleep needs. Research is needed into the benefits of napping and sleep extension (eg, banking sleep).

Hydration Marker Diagnostic Accuracy to Identify Mild Intracellular and Extracellular Dehydration.

Identifying mild dehydration (≤2% of body mass) is important to prevent the negative effects of more severe dehydration on human health and performance. It is unknown whether a single hydration marker can identify both mild intracellular dehydration (ID) and extracellular dehydration (ED) with adequate diagnostic accuracy (≥0.7 receiver-operating characteristic-area under the curve [ROC-AUC]). Thus, in 15 young healthy men, the authors determined the diagnostic accuracy of 15 hydration markers after three randomized 48-hr trials; euhydration (water 36 ml·kg-1·day-1), ID caused by exercise and 48 hr of fluid restriction (water 2 ml·kg-1·day-1), and ED caused by a 4-hr diuretic-induced diuresis begun at 44 hr (Furosemide 0.65 mg/kg). Body mass was maintained on euhydration, and dehydration was mild on ID and ED (1.9% [0.5%] and 2.0% [0.3%] of body mass, respectively). Urine color, urine specific gravity, plasma osmolality, saliva flow rate, saliva osmolality, heart rate variability, and dry mouth identified ID (ROC-AUC; range 0.70-0.99), and postural heart rate change identified ED (ROC-AUC 0.82). Thirst 0-9 scale (ROC-AUC 0.97 and 0.78 for ID and ED) and urine osmolality (ROC-AUC 0.99 and 0.81 for ID and ED) identified both dehydration types. However, only the thirst 0-9 scale had a common dehydration threshold (≥4; sensitivity and specificity of 100%; 87% and 71%, 87% for ID and ED). In conclusion, using a common dehydration threshold ≥4, the thirst 0-9 scale identified mild intracellular and ED with adequate diagnostic accuracy. In young healthy adults', thirst 0-9 scale is a valid and practical dehydration screening tool.

Sucrose and Sodium but not Caffeine Content Influence the Retention of Beverages in Humans Under Euhydrated Conditions.

This study systematically examined the influence of carbohydrate (sucrose), sodium, and caffeine on the fluid retention potential of beverages under euhydrated conditions, using the beverage hydration index method. Three cohorts, each of 12 young, healthy, active men, ingested 1 L of beverages containing four different concentrations of a single component (sucrose, sodium, or caffeine) in a double-blind, crossover manner. Urine output was collected for the subsequent 4 hr. Cumulative urine output was lower and net fluid balance was higher after 10 and 20% sucrose beverages than 0 and 5% sucrose beverages (p < .05), and after 27 and 52 mmol/L sodium beverages than 7 and 15 mmol/L sodium beverages (p < .05). No difference in urine output or net fluid balance was apparent following ingestion of caffeine at concentrations of 0-400 mg/L (p = .83). Consequently, the calculated beverage hydration index was greater in beverages with higher sucrose or sodium content, but caffeine had no effect. No difference was observed in arginine vasopressin or aldosterone between any trials. These data highlight that the key drivers promoting differences in the fluid retention potential of beverages when euhydrated are energy density, likely through slowed fluid delivery to the circulation (carbohydrate content effect), or electrolyte content through improved fluid retention (sodium content effect). These data demonstrate that beverage carbohydrate and sodium content influence fluid delivery and retention in the 4 hr after ingestion, but caffeine up to 400 mg/L does not. Athletes and others can use this information to guide their daily hydration practices.

Anxiety and perceived psychological stress play an important role in the immune response after exercise.

There are common pathways by which psychological stress and exercise stress alter immunity. However, it remains unknown whether psychological stress plays a role in the in vivo immune response to exercise. We examined the relationship between anxiety and perceived psychological stress reported before exercise and in vivo immunity after exercise using skin sensitisation with Diphenylcyclopropenone (DPCP). In a randomised design, sixty four, thoroughly familiarised, males completed widely used psychological instruments to assess state-anxiety and perceived psychological stress before exercise, and ran either 30 minutes at 60% (30MI) or 80% (30HI) V . O2peak, 120 minutes at 60% (120MI) V . O2peak or rested (CON) before DPCP sensitisation. Cutaneous recall to DPCP was measured as the dermal thickening response to a low-dose series DPCP challenge 4-weeks after sensitisation. After accounting for exercise (R2 = 0.20; P < 0.01), multiple-regression showed that pre-exercise state-anxiety (STAI-S; ΔR2 = 0.19; P < 0.01) and perceived psychological stress (ΔR2 = 0.13; P < 0.05) were moderately associated with the DPCP response after exercise. The STAI-S scores before exercise were considered low-to-moderate in these familiarised individuals (median split; mean STAI-S of low 25 and moderate 34). Further examination showed that the DPCP response after exercise (30MI, 30HI or 120MI) was 62% lower in those reporting low vs. moderate state-anxiety before exercise (mean difference in dermal thickening: -2.6 mm; 95% CI: -0.8 to -4.4 mm; P < 0.01). As such, the results indicate a beneficial effect of moderate (vs. low) state-anxiety and perceived psychological stress on in vivo immunity after exercise. Moreover, correlations were of comparable strength for the relationship between physiological stress (heart rate training impulse) and the summed dermal response to DPCP (r = -0.37; 95% CI: -0.05 to -0.62; P = 0.01), and state-anxiety and the summed dermal response to DPCP (r = 0.39; 95% CI: 0.08 to 0.63; P < 0.01). In conclusion, state-anxiety and perceived psychological stress levels before exercise play animportant role in determining the strength of the in vivo immune response after exercise. These findings indicate a similar strength relationship for the level of state-anxiety prior to exercise and the level of physiological stress during exercise with the in vivo immune response after exercise. Future research is required to investigate exercise-immune responses in athletes, military personnel and others in physically demanding occupations experiencing higher levels of psychological stress than those reported in this study e.g. related to important competition, military operations and major life events. Nevertheless, the present findings support the recommendation that exercise scientists should account for anxiety and psychological stress when examining the immune response to exercise.

IOC consensus statement: dietary supplements and the high-performance athlete.

Nutrition usually makes a small but potentially valuable contribution to successful performance in elite athletes, and dietary supplements can make a minor contribution to this nutrition programme. Nonetheless, supplement use is widespread at all levels of sport. Products described as supplements target different issues, including (1) the management of micronutrient deficiencies, (2) supply of convenient forms of energy and macronutrients, and (3) provision of direct benefits to performance or (4) indirect benefits such as supporting intense training regimens. The appropriate use of some supplements can benefit the athlete, but others may harm the athlete's health, performance, and/or livelihood and reputation (if an antidoping rule violation results). A complete nutritional assessment should be undertaken before decisions regarding supplement use are made. Supplements claiming to directly or indirectly enhance performance are typically the largest group of products marketed to athletes, but only a few (including caffeine, creatine, specific buffering agents and nitrate) have good evidence of benefits. However, responses are affected by the scenario of use and may vary widely between individuals because of factors that include genetics, the microbiome and habitual diet. Supplements intended to enhance performance should be thoroughly trialled in training or simulated competition before being used in competition. Inadvertent ingestion of substances prohibited under the antidoping codes that govern elite sport is a known risk of taking some supplements. Protection of the athlete's health and awareness of the potential for harm must be paramount; expert professional opinion and assistance is strongly advised before an athlete embarks on supplement use.

IOC Consensus Statement: Dietary Supplements and the High-Performance Athlete.

Nutrition usually makes a small but potentially valuable contribution to successful performance in elite athletes, and dietary supplements can make a minor contribution to this nutrition program. Nonetheless, supplement use is widespread at all levels of sport. Products described as supplements target different issues, including the management of micronutrient deficiencies, supply of convenient forms of energy and macronutrients, and provision of direct benefits to performance or indirect benefits such as supporting intense training regimens. The appropriate use of some supplements can offer benefits to the athlete, but others may be harmful to the athlete's health, performance, and/or livelihood and reputation if an anti-doping rule violation results. A complete nutritional assessment should be undertaken before decisions regarding supplement use are made. Supplements claiming to directly or indirectly enhance performance are typically the largest group of products marketed to athletes, but only a few (including caffeine, creatine, specific buffering agents and nitrate) have good evidence of benefits. However, responses are affected by the scenario of use and may vary widely between individuals because of factors that include genetics, the microbiome, and habitual diet. Supplements intended to enhance performance should be thoroughly trialed in training or simulated competition before implementation in competition. Inadvertent ingestion of substances prohibited under the anti-doping codes that govern elite sport is a known risk of taking some supplements. Protection of the athlete's health and awareness of the potential for harm must be paramount, and expert professional opinion and assistance is strongly advised before embarking on supplement use.

Consensus Statement Immunonutrition and Exercise.

In this consensus statement on immunonutrition and exercise, a panel of knowledgeable contributors from across the globe provides a consensus of updated science, including the background, the aspects for which a consensus actually exists, the controversies and, when possible, suggested directions for future research.

Exercise, immune function and respiratory infection: An update on the influence of training and environmental stress.

This review outlines recent advancements in the understanding of athlete immune health. Controversies discussed include whether high levels of athletic training and environmental stress (for example, heat acclimation, cryotherapy and hypoxic training) compromise immunity and increase upper respiratory tract infection (URTI). Recent findings challenge early exercise immunology doctrine by showing that international athletes performing high-volume training suffer fewer, not greater, URTI episodes than lower-level performers and URTI incidence decreases, not increases, around the time of competition compared with heavy training. Herein we raise the possibility of host genetic influences on URTI and modifiable behavioural and training-related factors underpinning these recent observations. Continued controversy concerns the proportion of URTI symptoms reported by athletes that are due to infectious pathogens, airway inflammation or as yet unknown causes and indeed whether the proportion differs in athletes and non-athletes. Irrespective of the cause of URTI symptoms (infectious or non-infectious), experts broadly agree that self-reported URTI hinders high-volume athletic training but, somewhat surprisingly, less is known about the influence on athletic performance. In athletes under heavy training, both innate and acquired immunity are often observed to decrease, typically 15-25%, but whether relatively modest changes in immunity increase URTI susceptibility remains a major gap in knowledge. With the exception of cell-mediated immunity that tends to be decreased, exercising in environmental extremes does not provide an additional threat to immunity and host defence. Recent evidence suggests that immune health may actually be enhanced by regular intermittent exposures to environmental stress (for example, intermittent hypoxia training).

Diagnosing dehydration? Blend evidence with clinical observations.

PURPOSE OF REVIEW: The purpose of the review is to provide recommendations to improve clinical decision-making based on the strengths and weaknesses of commonly used hydration biomarkers and clinical assessment methods. RECENT FINDINGS: There is widespread consensus regarding treatment, but not the diagnosis of dehydration. Even though it is generally accepted that a proper clinical diagnosis of dehydration can only be made biochemically rather than relying upon clinical signs and symptoms, no gold standard biochemical hydration index exists. Other than clinical biomarkers in blood (i.e., osmolality and blood urea nitrogen/creatinine) and in urine (i.e., osmolality and specific gravity), blood pressure assessment and clinical symptoms in the eye (i.e., tear production and palpitating pressure) and the mouth (i.e., thirst and mucous wetness) can provide important information for diagnosing dehydration. SUMMARY: We conclude that clinical observations based on a combination of history, physical examination, laboratory values, and clinician experience remain the best approach to the diagnosis of dehydration.

Is there an optimal vitamin D status for immunity in athletes and military personnel?

Vitamin D is mainly obtained through sunlight ultraviolet-B (UVB) exposure of the skin, with a small amount typically coming from the diet.It is now clear that vitamin D has important roles beyond its well-known effects on calcium and bone homeostasis. Immune cells express the vitamin D receptor, including antigen presenting cells, T cells and B cells, and these cells are all capable of synthesizing the biologically active vitamin D metabolite, 1, 25 hydroxy vitamin D.There has been growing interest in the benefits of supplementing vitamin D as studies report vitamin D insufficiency (circulating 25(OH)D < 50 nmol/L) in more than half of all athletes and military personnel tested during the winter, when skin sunlight UVB is negligible. The overwhelming evidence supports avoiding vitamin D deficiency (25(OH)D< 30 nmol/L)to maintain immunity and prevent upper respiratory illness (URI) in athletes and military personnel.Recent evidence supports an optimal circulating 25(OH)D of 75 nmol/L to prevent URI and enhance innate immunity and mucosal immunity and bring about anti-inflammatory actions through the induction of regulatory T cells and the inhibition of pro-inflammatory cytokine production. We provide practical recommendations for how vitamin D sufficiency can be achieved in most individuals by safe sunlight exposure in the summer and daily 1, 000 IU vitamin D3 supplementation in the winter. Studies are required in athletes and military personnel to determine the impact of these recommendations on immunity and URI; and,to demonstrate the purported benefit of achieving 25(OH)D>75 nmol/L.

Carbohydrate supplementation does not blunt the prolonged exercise-induced reduction of in vivo immunity.

BACKGROUND: Carbohydrate (CHO) supplementation during prolonged exercise is widely acknowledged to blunt in vitro immunoendocrine responses, but no study has investigated in vivo immunity. PURPOSE: To determine the effect of CHO supplementation during prolonged exercise on in vivo immune induction using experimental contact hypersensitivity with the novel antigen diphenylcyclopropenone (DPCP). METHODS: In a double-blind design, 32 subjects were randomly assigned to 120 min of treadmill exercise at 60 % [Formula: see text] with CHO (Ex-CHO) or placebo (Ex-PLA) supplementation. Responses were also compared to 16 resting control (CON) subjects from a previous study (for additional comparison with a resting non-exercise condition). Standardised diets (24 h pre-trial) and breakfasts (3.5 h pre-trial) were provided. Subjects received a primary DPCP exposure (sensitisation) 20 min after trial completion, and exactly 28 days later the strength of immune reactivity was quantified by magnitude of the cutaneous response (skin-fold thickness and erythema) to a low dose-series DPCP challenge. Stress hormones and leucocyte trafficking were also monitored. RESULTS: CHO supplementation blunted the cortisol and leucocyte trafficking responses, but there was no difference (P > 0.05) between Ex-CHO and Ex-PLA in the in vivo immune responses (e.g. both ~46 % lower than CON for skin-fold response). CONCLUSIONS: CHO supplementation does not influence the decrease in in vivo immunity seen after prolonged exercise. The effects with more stressful (or fasted) exercise remain to be determined. However, there appears to be no benefit under the conditions of the present study, which have practical relevance to what many athletes do in training or competition.

Portable Prehospital Methods to Treat Near-Hypothermic Shivering Cold Casualties.

OBJECTIVE: To compare the effectiveness of a single-layered polyethylene survival bag (P), a single-layered polyethylene survival bag with a hot drink (P+HD), a multi-layered metalized plastic sheeting survival bag (MPS: Blizzard Survival), and a multi-layered MPS survival bag with 4 large chemical heat pads (MPS+HP: Blizzard Heat) to treat cold casualties. METHODS: Portable cold casualty treatment methods were compared by examining core and skin temperature, metabolic heat production, and thermal comfort during a 3-hour, 0°C cold air exposure in 7 shivering, near-hypothermic men (35.4°C). The hot drink (70°C, ~400 ml, ~28 kJ) was consumed at 0, 1, and 2 hours during the cold air exposure. RESULTS: During the cold air exposure, core rewarming and thermal comfort were similar on all trials (P = .45 and P = .36, respectively). However, skin temperature was higher (10%-13%; P < .001; large effect sizes d > 2.7) and metabolic heat production lower (15%-39%; P < .05; large effect sizes d > .9) on MPS and MPS+HP than P and P+HD. The addition of heat pads further lowered metabolic heat production by 15% (MPS+HP vs MPS; P = .05; large effect size d = .9). The addition of the hot drink to polyethylene survival bag did not increase skin temperature or lower metabolic heat production. CONCLUSIONS: Near-hypothermic cold casualties are rewarmed with less peripheral cold stress and shivering thermogenesis using a multi-layered MPS survival bag compared with a polyethylene survival bag. Prehospital rewarming is further aided by large chemical heat pads but not by hot drinks.

Clinical symptoms, signs and tests for identification of impending and current water-loss dehydration in older people.

BACKGROUND: There is evidence that water-loss dehydration is common in older people and associated with many causes of morbidity and mortality. However, it is unclear what clinical symptoms, signs and tests may be used to identify early dehydration in older people, so that support can be mobilised to improve hydration before health and well-being are compromised. OBJECTIVES: To determine the diagnostic accuracy of state (one time), minimally invasive clinical symptoms, signs and tests to be used as screening tests for detecting water-loss dehydration in older people by systematically reviewing studies that have measured a reference standard and at least one index test in people aged 65 years and over. Water-loss dehydration was defined primarily as including everyone with either impending or current water-loss dehydration (including all those with serum osmolality ≥ 295 mOsm/kg as being dehydrated). SEARCH METHODS: Structured search strategies were developed for MEDLINE (OvidSP), EMBASE (OvidSP), CINAHL, LILACS, DARE and HTA databases (The Cochrane Library), and the International Clinical Trials Registry Platform (ICTRP). Reference lists of included studies and identified relevant reviews were checked. Authors of included studies were contacted for details of further studies. SELECTION CRITERIA: Titles and abstracts were scanned and all potentially relevant studies obtained in full text. Inclusion of full text studies was assessed independently in duplicate, and disagreements resolved by a third author. We wrote to authors of all studies that appeared to have collected data on at least one reference standard and at least one index test, and in at least 10 people aged ≥ 65 years, even where no comparative analysis has been published, requesting original dataset so we could create 2 x 2 tables. DATA COLLECTION AND ANALYSIS: Diagnostic accuracy of each test was assessed against the best available reference standard for water-loss dehydration (serum or plasma osmolality cut-off ≥ 295 mOsm/kg, serum osmolarity or weight change) within each study. For each index test study data were presented in forest plots of sensitivity and specificity. The primary target condition was water-loss dehydration (including either impending or current water-loss dehydration). Secondary target conditions were intended as current (> 300 mOsm/kg) and impending (295 to 300 mOsm/kg) water-loss dehydration, but restricted to current dehydration in the final review.We conducted bivariate random-effects meta-analyses (Stata/IC, StataCorp) for index tests where there were at least four studies and study datasets could be pooled to construct sensitivity and specificity summary estimates. We assigned the same approach for index tests with continuous outcome data for each of three pre-specified cut-off points investigated.Pre-set minimum sensitivity of a useful test was 60%, minimum specificity 75%. As pre-specifying three cut-offs for each continuous test may have led to missing a cut-off with useful sensitivity and specificity, we conducted post-hoc exploratory analyses to create receiver operating characteristic (ROC) curves where there appeared some possibility of a useful cut-off missed by the original three. These analyses enabled assessment of which tests may be worth assessing in further research. A further exploratory analysis assessed the value of combining the best two index tests where each had some individual predictive ability. MAIN RESULTS: There were few published studies of the diagnostic accuracy of state (one time), minimally invasive clinical symptoms, signs or tests to be used as screening tests for detecting water-loss dehydration in older people. Therefore, to complete this review we sought, analysed and included raw datasets that included a reference standard and an index test in people aged ≥ 65 years.We included three studies with published diagnostic accuracy data and a further 21 studies provided datasets that we analysed. We assessed 67 tests (at three cut-offs for each continuous outcome) for diagnostic accuracy of water-loss dehydration (primary target condition) and of current dehydration (secondary target condition).Only three tests showed any ability to diagnose water-loss dehydration (including both impending and current water-loss dehydration) as stand-alone tests: expressing fatigue (sensitivity 0.71 (95% CI 0.29 to 0.96), specificity 0.75 (95% CI 0.63 to 0.85), in one study with 71 participants, but two additional studies had lower sensitivity); missing drinks between meals (sensitivity 1.00 (95% CI 0.59 to 1.00), specificity 0.77 (95% CI 0.64 to 0.86), in one study with 71 participants) and BIA resistance at 50 kHz (sensitivities 1.00 (95% CI 0.48 to 1.00) and 0.71 (95% CI 0.44 to 0.90) and specificities of 1.00 (95% CI 0.69 to 1.00) and 0.80 (95% CI 0.28 to 0.99) in 15 and 22 people respectively for two studies, but with sensitivities of 0.54 (95% CI 0.25 to 0.81) and 0.69 (95% CI 0.56 to 0.79) and specificities of 0.50 (95% CI 0.16 to 0.84) and 0.19 (95% CI 0.17 to 0.21) in 21 and 1947 people respectively in two other studies). In post-hoc ROC plots drinks intake, urine osmolality and axillial moisture also showed limited diagnostic accuracy. No test was consistently useful in more than one study.Combining two tests so that an individual both missed some drinks between meals and expressed fatigue was sensitive at 0.71 (95% CI 0.29 to 0.96) and specific at 0.92 (95% CI 0.83 to 0.97).There was sufficient evidence to suggest that several stand-alone tests often used to assess dehydration in older people (including fluid intake, urine specific gravity, urine colour, urine volume, heart rate, dry mouth, feeling thirsty and BIA assessment of intracellular water or extracellular water) are not useful, and should not be relied on individually as ways of assessing presence or absence of dehydration in older people.No tests were found consistently useful in diagnosing current water-loss dehydration. AUTHORS' CONCLUSIONS: There is limited evidence of the diagnostic utility of any individual clinical symptom, sign or test or combination of tests to indicate water-loss dehydration in older people. Individual tests should not be used in this population to indicate dehydration; they miss a high proportion of people with dehydration, and wrongly label those who are adequately hydrated.Promising tests identified by this review need to be further assessed, as do new methods in development. Combining several tests may improve diagnostic accuracy.