Nutritional modulation of exercise-induced immunodepression in athletes: a systematic review and meta-analysis

Nutraceuticals as Modulators of Immune Function: A Review of Potential Therapeutic Effects

Dietary supplementation with nutraceuticals can promote optimal immune system activation, modulating different pathways that enhance immune defenses. Therefore, the immunity-boosting effects of nutraceuticals encompass not only immunomodulatory but also antioxidant, antitumor, antiviral, antibacterial, and antifungal properties, with therapeutic effects against diverse pathological conditions. However, the complexity of the pathways that regulate the immune system, numerous mechanisms of action, and heterogeneity of the immunodeficiencies, and subjects treated make their application in the clinical field difficult. Some nutraceuticals appear to safely improve immune system function, particularly by preventing viral and bacterial infections in specific groups, such as children, the elderly, and athletes, as well as in frail patients, such as those affected by autoimmune diseases, chronic diseases, or cancer. Several nutraceuticals, such as vitamins, mineral salts, polyunsaturated omega-3 fatty acids, many types of phytocompounds, and probiotic strains, have the most consolidated evidence in humans. In most cases, further large and long-term randomized clinical trials are needed to confirm the available preliminary positive data.

Low-carbohydrate diets and men's cortisol and testosterone: Systematic review and meta-analysis

Background: Low-carbohydrate diets may have endocrine effects, although individual studies are conflicting. Therefore, a review was conducted on the effects of low- versus high-carbohydrate diets on men's testosterone and cortisol. Methods: The review was registered on PROSPERO (CRD42021255957). The inclusion criteria were: intervention study, healthy adult males, and low-carbohydrate diet: ≤35% carbohydrate. Eight databases were searched from conception to May 2021. Cochrane's risk of bias tool was used for quality assessment. Random-effects, meta-analyses using standardized mean differences and 95% confidence intervals, were performed with Review Manager. Subgroup analyses were conducted for diet duration, protein intake, and exercise duration. Results: Twenty-seven studies were included, with a total of 309 participants. Short-term (<3 weeks), low- versus high-carbohydrate diets moderately increased resting cortisol (0.41 [0.16, 0.66], p < 0.01). Whereas, long-term (≥3 weeks), low-carbohydrate diets had no consistent effect on resting cortisol. Low- versus high-carbohydrate diets resulted in much higher post-exercise cortisol, after long-duration exercise (≥20 min): 0 h (0.78 [0.47, 1.1], p < 0.01), 1 h (0.81 [0.31, 1.31], p < 0.01), and 2 h (0.82 [0.33, 1.3], p < 0.01). Moderate-protein (<35%), low-carbohydrate diets had no consistent effect on resting total testosterone, however high-protein (≥35%), low-carbohydrate diets greatly decreased resting (-1.08 [-1.67, -0.48], p < 0.01) and post-exercise total testosterone (-1.01 [-2, -0.01] p = 0.05). Conclusions: Resting and post-exercise cortisol increase during the first 3 weeks of a low-carbohydrate diet. Afterwards, resting cortisol appears to return to baseline, whilst post-exercise cortisol remains elevated. High-protein diets cause a large decrease in resting total testosterone (∼5.23 nmol/L).

The Potential Role of Korean Mistletoe Extract as an Anti-Inflammatory Supplementation

Korean mistletoe has anti-inflammatory and antioxidant functions and may be a useful training supplement. We investigated the effect of Korean mistletoe extract (KME) on inflammatory markers after high-intensity exercise by 20 university male rowers (KME group vs. CON group) consuming 110 mL KME/dose (2 times a day over 8 weeks). Blood samples were collected for measurement of serum cytokine levels at baseline, immediately after exercise, and following 30 minutes of recovery. Interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and C-reactive protein (CRP) were used as markers for inflammation. After supplementation, IL-6 and TNF-α levels were significantly lowered in the KME group than in the CON group at baseline, immediately after exercise, and following 30 minutes of recovery. KME can reduce high-strength exercise-induced increases in the levels of serum inflammatory cytokines in active individuals and improve anti-inflammatory functions.

Immunomodulating Effects of Fungal Beta-Glucans: From Traditional Use to Medicine

The importance of a well-functioning and balanced immune system has become more apparent in recent decades. Various elements have however not yet been uncovered as shown, for example, in the uncertainty on immune system responses to COVID-19. Fungal beta-glucans are bioactive molecules with immunomodulating properties. Insights into the effects and function of beta-glucans, which have been used in traditional Chinese medicine for centuries, advances with the help of modern immunological and biotechnological methods. However, it is still unclear into which area beta-glucans fit best: supplements or medicine? This review has highlighted the potential application of fungal beta-glucans in nutrition and medicine, reviewing their formulation, efficacy, safety profile, and immunomodulating effects. The current status of dietary fungal glucans with respect to the European scientific requirements for health claims related to the immune system and defense against pathogens has been reviewed. Comparing the evidence base of the putative health effects of fungal beta-glucan supplements with the published guidance documents by EFSA on substantiating immune stimulation and pathogen defense by food products shows that fungal beta-glucans could play a role in supporting and maintaining health and, thus, can be seen as a good health-promoting substance from food, which could mean that this effect may also be claimed if approved. In addition to these developments related to food uses of beta-glucan-containing supplements, beta-glucans could also hold a novel position in Western medicine as the concept of trained immunity is relatively new and has not been investigated to a large extent. These innovative concepts, together with the emerging success of modern immunological and biotechnological methods, suggest that fungal glucans may play a promising role in both perspectives, and that there are possibilities for traditional medicine to provide an immunological application in both medicine and nutrition.

Multi-Micronutrient Supplementation and Immunoglobulin Response in Well-Fed Firefighters

Intensive physical training programs can affect the immune system. This study aims to verify the multi-micronutrient supplementation effects on serum immunoglobulins levels prior to and after a five-week physical training program. Twenty-four male recruit firefighters were randomly allocated into supplemented (with Prisfar Ever-Fit Plus over 35 consecutive days) and placebo groups (n=12 each). Serum immunoglobulins G, A, and M were assessed. Supplementation effect was detected for immunoglobulin G (eta-squared, η ² : 0.09; p =0.035; power: 0.56), A (η ² : 0.24; p =0.001; power: 0.95), and M (η ² : 0.09; p =0.036; power: 0.56). Although immunoglobulin A was different between groups at baseline (mean difference: 42.58; 95%CI: 7.00 to 78.16 mg/dL; p =0.021; d =2.48), within-group (before vs . after five weeks) showed no differences for both supplemented and control groups. In addition, even if immunoglobulin G and M were similar at baseline, immunoglobulin G decreased (mean diff.: 46.4; 95%CI: 6.7 to 86.1 mg/dL; p =0.03; d =0.74) and immunoglobulin M increased (mean diff.: -10.7; 95%CI: -15.8 to -5.5 mg/dL; p =0.001; d =-1.33) in the control group. Although mean values remained within the reference values, changes observed for immunoglobulin G and M may reflect some immune protection for firefighters engaged in recruit training.

The Effect of Acute Glutamine Supplementation on Markers of Inflammation and Fatigue During Consecutive Days of Simulated Wildland Firefighting

OBJECTIVE

To examine the effect of oral glutamine supplementation on inflammation and fatigue during and after simulated wildland firefighting (WLFF) tasks in hot conditions over 2 consecutive days.

METHODS

Eleven men and women ingested a glutamine supplement or a placebo before and after simulated wildland firefighting in an environmental chamber (38 °C, 35% relative humidity). Subjective fatigue, markers of inflammation, and cellular stress were measured pre, post and 4 hours post-exercise on both days.

RESULTS

Gastrointestinal damage, subjective fatigue, and ratings of perceived exertion were lower after glutamine supplementation compared with placebo. Heat shock protein 70 (HSP70) and nuclear factor kappa-inhibitor alpha (IκBα) levels were higher on both days of the glutamine trial compared with placebo.

CONCLUSIONS

Glutamine supplementation may improve recovery after fire suppression in WLFFs. This may result from the upregulation of HSP70 which inhibits inflammation and protects against gastrointestinal (GI) barrier damage.

Identification of Urinary Biomarkers for Exercise-Induced Immunosuppression by iTRAQ Proteomics

Purpose

To identify noninvasive immune biomarkers of exercise-induced immunosuppression using the iTRAQ proteomics technique.

Methods

Fifteen healthy males were recruited and subjected to a four-week incremental treadmill running training program. After each week of training, WBC counts and CD4⁺ and CD8⁺ lymphocytes were measured to monitor the immune function status. iTRAQ proteomics technology was used to identify differential proteins and their characteristics in urine.

Results

Our data showed that the WBC counts, CD4⁺ lymphocytes, and CD4⁺/CD8⁺ ratio decreased by more than 10% after four weeks of training, suggesting exercise-induced immunosuppression. A total of 1854 proteins were identified in urine during the incremental running using the iTRAQ technology. Compared with the urine before training, there were 89, 52, 77, and 148 proteins significantly upregulated and 66, 27, 68, and 114 proteins significantly downregulated after each week, respectively. Among them, four upregulated proteins, SEMG-1, PIP, PDGFRL, and NDPK, increased their abundance with the increased exercise intensity. Bioinformatics analysis indicates that these proteins are involved in stress response and immune function.

Conclusion

Four weeks of incremental treadmill running induced immunosuppression in healthy males. By using iTRAQ proteomics, four proteins in the urine, SEMG-1, PIP, PDGFRL, and NDPK, were found to increase incrementally with the increased exercise intensity, which have the potential to be used as noninvasive immune biomarkers of exercise-induced immunosuppression.

A Review of Micronutrients and the Immune System-Working in Harmony to Reduce the Risk of Infection

Immune support by micronutrients is historically based on vitamin C deficiency and supplementation in scurvy in early times. It has since been established that the complex, integrated immune system needs multiple specific micronutrients, including vitamins A, D, C, E, B6, and B12, folate, zinc, iron, copper, and selenium, which play vital, often synergistic roles at every stage of the immune response. Adequate amounts are essential to ensure the proper function of physical barriers and immune cells; however, daily micronutrient intakes necessary to support immune function may be higher than current recommended dietary allowances. Certain populations have inadequate dietary micronutrient intakes, and situations with increased requirements (e.g., infection, stress, and pollution) further decrease stores within the body. Several micronutrients may be deficient, and even marginal deficiency may impair immunity. Although contradictory data exist, available evidence indicates that supplementation with multiple micronutrients with immune-supporting roles may modulate immune function and reduce the risk of infection. Micronutrients with the strongest evidence for immune support are vitamins C and D and zinc. Better design of human clinical studies addressing dosage and combinations of micronutrients in different populations are required to substantiate the benefits of micronutrient supplementation against infection.

Respiratory Infections

Respiratory infections are the most frequent cause of athletes’ visits in medical practices. Simultaneously, contradictory beliefs are generally held regarding influence of repeated exercise on immunity reflected in susceptibility to infections. Many tend to claim that exercise weakens the immunity and renders regular exercisers more prone to develop airway infections. On the other hand, voices are heard in favor of the possible beneficial influence of regular exercise on immune system efficiency. This chapter focuses on the associations of various kinds of exercise with respiratory infection susceptibility. Influence of exercise, in particular associated with competitive performance, on selected innate and acquired immune response mechanisms is also addressed.

Effects of Protein Versus Carbohydrate Supplementation on Markers of Immune Response in Master Triathletes: A Randomized Controlled Trial

Objective: This study examines the long-term effects of ingesting hydrolyzed beef protein versus carbohydrate on indirect markers of immunity during 10 weeks of endurance training in master-aged triathletes (n = 16, age 35-60 years). Methods: Participants were randomly assigned to either a hydrolyzed beef protein (PRO, n = 8) or nonprotein isoenergetic carbohydrate (CHO, n = 8) condition, which consisted of ingesting 20 g of each supplement, mixed with water, once a day immediately post workout, or before breakfast on nontraining days. Salivary human neutrophil peptides (HNP1-3) were measured before and after performing an incremental endurance test to volitional exhaustion at both pre and post intervention. Additionally, baseline levels of platelets, neutrophils, eosinophil basophils, monocytes, and lymphocytes were determined at pre and post intervention. Results: No significant changes in baseline concentration and secretion rate of salivary HNP1-3 were observed for either treatment. The CHO group showed a nonsignificant decrease in resting HNP1-3 concentrations following the intervention (p = 0.052, effect size d = 0.53). Protein supplementation demonstrated a significant reduction in lymphocyte counts pre to post intervention (mean [SD]: 2.30 [0.57] vs. 1.93 [0.45] 10³/mm³, p = 0.046, d = 0.77), along with a moderate but not statistically significant increase (d = 0.75, p = 0.051) of the neutrophil-to-lymphocyte ratio. Conclusions: In master-aged triathletes, postworkout ingestion of only protein, with no carbohydrate, may not be as effective as carbohydrate alone to attenuate negative long-term changes of some salivary and cellular immunological markers. Future studies should consider the co-ingestion of both macronutrients.

Clinical and laboratory factors contributing to uninterpretable beryllium lymphocyte proliferation tests (BeLPT)

BACKGROUND

The beryllium lymphocyte proliferation test (BeLPT), has become the principal clinical test for detecting beryllium sensitization and chronic beryllium disease. Uninterpretable BeLPT results can occur in a small but significant proportion of tests from poor lymphocyte growth (PG) or over proliferation of lymphocytes (OP). The clinical and laboratory causes of uninterpretable results are not known.

METHODS

BeLPT data from the US Department of Energy-supported Former Worker Screening Program were analyzed for a 10-year period. Drivers of uninterpretable BeLPTs were investigated using multivariable models and classification techniques.

RESULTS

Three participant attributes were significantly associated with PG, while OP showed no significant associations. Serum lot for the lymphocyte growth medium accounted for 21% of the variation in PG and 16% in OP.

CONCLUSION

Serum lots influence the likelihood of having uninterpretable BeLPT. To better understand uninterpretable results and possibly reduce their occurrence, additional laboratory-related factors should be addressed.

Amino acids and sport: a true love story?

Among a plethora of dietary supplements, amino acids are very popular with athletes for several reasons (e.g., to prevent nutritional deficiency, improve muscle function, and decrease muscle damages) whose purpose is to improve performance. However, it is difficult to get a clear idea of which amino acids have real ergogenic impact. Here, we review and analyze the clinical studies evaluating specific amino acids (glutamine, arginine, leucine, etc.) in athletes. Only english-language clinical studies evaluating a specific effect of one amino acid were considered. Despite promising results, many studies have methodological limits or specific flaws that do not allow definitive conclusions. To date, only chronic β-alanine supplementation demonstrated an ergogenic effect in athletes. Much research is still needed to gain evidence-based data before any other specific amino acid can be recommended for use in athletes.

Vitamin A Oral Supplementation Induces Oxidative Stress and Suppresses IL-10 and HSP70 in Skeletal Muscle of Trained Rats

Exercise training intensity is the major variant that influences the relationship between exercise, redox balance, and immune response. Supplement intake is a common practice for oxidative stress prevention; the effects of vitamin A (VA) on exercise training are not yet described, even though this molecule exhibits antioxidant properties. We investigated the role of VA supplementation on redox and immune responses of adult Wistar rats subjected to swimming training. Animals were divided into four groups: sedentary, sedentary + VA, exercise training, and exercise training + VA. Over eight weeks, animals were submitted to intense swimming 5 times/week and a VA daily intake of 450 retinol equivalents/day. VA impaired the total serum antioxidant capacity acquired by exercise, with no change in interleukin-1β and tumor necrosis factor-α levels. In skeletal muscle, VA caused lipid peroxidation and protein damage without differences in antioxidant enzyme activities; however, Western blot analysis showed that expression of superoxide dismutase-1 was downregulated, and upregulation of superoxide dismutase-2 induced by exercise was blunted by VA. Furthermore, VA supplementation decreased anti-inflammatory interleukin-10 and heat shock protein 70 expression, important factors for positive exercise adaptations and tissue damage prevention. Our data showed that VA supplementation did not confer any antioxidative and/or protective effects, attenuating exercise-acquired benefits in the skeletal muscle.

Assisting the Novice in Lifestyle Change

The beginning of a lifestyle intervention is a sensitive time, as doing "too much too quickly" may stress the immune system, resulting in an increase in upper respiratory symptoms and, consequently, attrition. However, "too little too slowly" may not align with patients' motivation to change and may also result in attrition. There is also evidence that early weight loss is predictive of long-term maintenance of goal weight. Health care providers are frequently presented with contradictory information on the best model to promote enduring lifestyle change. Best practice dictates that health care provider acknowledge their patients' motivation to change and incorporate each individual's goals in designing the lifestyle change intervention. Additional support and advice may be warranted at the beginning of an intervention to promote the patient's health and avoid attrition.

Late-Pregnancy Salivary Cortisol Concentrations of Ghanaian Women Participating in a Randomized Controlled Trial of Prenatal Lipid-Based Nutrient Supplements

BACKGROUND

High circulating cortisol is associated with miscarriage, preterm birth, and low birth weight. Research in nonpregnant individuals suggests that improved nutrition may lower cortisol concentrations. It is unknown whether nutritional supplementation during pregnancy lowers cortisol.

OBJECTIVE

Our objective was to determine whether women receiving a lipid-based nutrient supplement (LNS) throughout pregnancy would have lower salivary cortisol at 36 wk gestation compared with women receiving other nutrient supplements.

METHODS

We conducted a randomized controlled trial in 1320 pregnant Ghanaian women at ≤20 wk gestation who were assigned to receive daily throughout pregnancy: 1) 60 mg iron + 400 μg folic acid (IFA), 2) multiple micronutrients (MMNs), or 3) 20 g LNS (containing 118 kcal, 22 micronutrients, and protein). Morning salivary cortisol was collected from a subsample at baseline and at 28 and 36 wk gestation.

RESULTS

A total of 758 women had cortisol measurements at 28 or 36 wk gestation. Salivary cortisol at 36 wk gestation did not differ between groups and was (mean ± SE) 7.97 ± 0.199 in the IFA group, 7.84 ± 0.191 in the MMN group, and 7.77 ± 0.199 nmol/L in the LNS group, when adjusted for baseline cortisol, time of waking, and time between waking and saliva collection (P = 0.67). There was an interaction between supplementation group and women's age (continuous variable, P-interaction = 0.03); and when age was dichotomized by the median, significant differences in salivary cortisol concentrations between groups were seen in women ≤26 y of age (IFA = 8.23 ± 0.284 nmol/L, MMN = 8.20 ± 0.274 nmol/L, and LNS = 7.44 ± 0.284 nmol/L; P = 0.03) but not in women >26 y old (IFA = 7.71 ± 0.281 nmol/L, MMN = 7.50 ± 0.274 nmol/L, and LNS = 8.08 ± 0.281 nmol/L; P = 0.13).

CONCLUSIONS

We conclude that supplementation with LNSs or MMNs during pregnancy did not affect the cortisol concentration in the study population as a whole, in comparison with IFA, but that LNS consumption among younger women may lead to lower cortisol at 36 wk gestation. This trial was registered at clinicaltrials.gov as NCT00970866.

The role of sports and exercise in allergic disease: drawbacks and benefits

Although training and exercise have several benefits, overdoing it might not necessarily be a good thing. For instance, elite athletes have an increased risk for asthma and allergy. Several mechanisms can be implicated for this risk, which include the interplay between environmental training factors and athlete's personal risk factors, such as genetic susceptibility, neurogenic-mediated inflammation, and epithelial sensitivity. However, an overwhelming amount of scientific evidence shows the positive effects of sports as part of a healthy lifestyle. Training reduces breathlessness and asthma symptoms and attenuates Th2-mediated inflammatory responses. Taken together, the benefits far outweigh the potential hazards of training. An easily administered therapeutic healthy lifestyle intervention, which could be used alongside current treatment, must be developed.

A multi-ingredient containing carbohydrate, proteins L-glutamine and L-carnitine attenuates fatigue perception with no effect on performance, muscle damage or immunity in soccer players

We investigated the effects of ingesting a multi-ingredient (53 g carbohydrate, 14.5 g whey protein, 5 g glutamine, 1.5 g L-carnitine-L-tartrate) supplement, carbohydrate only, or placebo on intermittent performance, perception of fatigue, immunity, and functional and metabolic markers of recovery. Sixteen amateur soccer players ingested their respective treatments before, during and after performing a 90-min intermittent repeated sprint test. Primary outcomes included time for a 90-min intermittent repeated sprint test (IRS) followed by eleven 15 m sprints. Measurements included creatine kinase, myoglobin, interleukine-6, Neutrophil; Lymphocytes and Monocyte before (pre), immediately after (post), 1 h and 24 h after exercise testing period. Overall, time for the IRS and 15 m sprints was not different between treatments. However, the perception of fatigue was attenuated (P<0.001) for the multi-ingredient (15.9±1.4) vs. placebo (17.8±1.4) but not for the carbohydrate (17.0±1.9) condition. Several changes in immune/inflammatory indices were noted as creatine kinase peaked at 24 h while Interleukin-6 and myoglobin increased both immediately after and at 1 h compared with baseline (P<0.05) for all three conditions. However, Myoglobin (P<0.05) was lower 1 h post-exercise for the multi-ingredient (241.8±142.6 ng·ml(-1)) and CHO (265.4±187.8 ng·ml(-1)) vs. placebo (518.6±255.2 ng·ml(-1)). Carbohydrate also elicited lower neutrophil concentrations vs. multi-ingredient (3.9±1.5 10(9)/L vs. 4.9±1.8 10(9)/L, P = 0.016) and a reduced (P<0.05) monocytes count (0.36±0.09 10(9)/L) compared to both multi-ingredient (0.42±0.09 10(9)/L) and placebo (0.42±0.12 10(9)/L). In conclusion, multi-ingredient and carbohydrate supplements did not improve intermittent performance, inflammatory or immune function. However, both treatments did attenuate serum myoglobin, while only carbohydrate blunted post-exercise leukocytosis.

Nutritional and Physical Activity Interventions to Improve Immunity

Physical activity and nutrition are important in a healthy lifestyle with potential benefits to immunity often overlooked. Infection of the upper respiratory tract, and the associated symptoms, are the most frequent presentations to general practitioners and may have significant economic and social impact. In this review, we consider the role of physical activity and nutrition in improving immunity. Evidence suggests that regular moderate activity is particularly beneficial for immune enhancement and reducing the risk of infection. We also discuss some nutritional strategies. Unfortunately, the evidence for many is weak. Avoiding nutritional deficiencies seems the most pragmatic recommendation. This can be achieved with a balanced diet. Including a variety of fruits and vegetables may help ensure adequate intake of essential nutrients with little risk of excess intake of any single nutrient. Supplementation with individual nutrients is generally not recommended. Multinutrients may be beneficial for those with a preexisting deficiency but not if normal dietary intake is sufficient. Further benefit may be gained from some supplements including probiotics, bovine colostrum, and some plant-derived products (Echinacea, black elderberry, and some polyphenols) but only in specific situations/contexts. Individuals should consider their personal needs, use caution, and avoid the indiscriminate use of supplements.

Effects of Supplementation with BCAA and L-glutamine on Blood Fatigue Factors and Cytokines in Juvenile Athletes Submitted to Maximal Intensity Rowing Performance

[Purpose] This study was conducted to understand the impacts of BCAA (branched-chain amino acid) and glutamine supplementation on the degree of blood fatigue factor stimulation and cytokines along with performance of exercise at the maximal intensity. [Subjects] Five male juvenile elite rowing athletes participated in this study as the subjects; they took 3 tests and received placebo supplementation (PS), BCAA supplementation (BS), and glutamine supplementation (GS). [Methods] The exercise applied in the tests was 2,000 m of rowing at the maximal intensity using an indoor rowing machine, and blood samples were collected 3 times, while resting, at the end of exercise, and after 30 min of recovery, to analyze the blood fatigue factors (lactate, phosphorous, ammonia, creatine kinase (CK)) and blood cytokines (IL (interleukin)-6, 8, 15). [Results] The results of the analysis showed that the levels of blood phosphorous in the BS and GS groups at the recovery stage were decreased significantly compared with at the end of exercise, and the level of CK appeared lower in the GS group alone at recovery stage than at the end of exercise. The level of blood IL-15 in the PS and BS groups appeared higher at the end of exercise compared with the resting stage. [Conclusion] It seemed that glutamine supplementation had a positive effect on the decrease in fatigue factor stimulation at the recovery stage after maximal intensity exercise compared with supplementation with the placebo or BCAA. Besides, pre-exercise glutamine supplementation seemed to help enhance immune function and the defensive inflammatory reaction.

Excessive Exercise and Immunity: The J-Shaped Curve

Exercise modulates the innate and specific arms of the immune system with a marked intensity-dependent response. This response might be influenced by sex differences and other factors including age, nutrition status, and overall level of psychological stress.

Exercise immunology is the field that studies this area. In the 1990s, Dr. Nieman formulated the controversial “J-shaped hypothesis” to describe the relationship between exercise intensity and the risk of acquiring upper respiratory tract infections (URTI). This hypothesis suggests that moderate exercise has the ability to improve immune function above sedentary levels while high intensity exercise depresses the immune system. However, some methodological problems exist in studies of the J-curve which makes evidence more anecdotal than evidence-based regarding the role of moderate and intense exercise in the incidence of URTI. These limitations are presented in the chapter.

Immunomodulatory effect of pleuran (β-glucan from Pleurotus ostreatus) in children with recurrent respiratory tract infections

OBJECTIVES

Recurrent respiratory tract infections (RRTIs) represent a very important problem in daily clinical practice because of their significant contribution to morbidity in children. Several natural nutritional supplements have been used in the prevention of RRTIs, but the clinical efficacy of only a few preparations is supported by scientific evidence.

MATERIALS AND METHODS

In a double-blind, placebo-controlled, randomised, multicentre study, we have observed a group of 175 children (aged 5.65 ± 2.39 years) with more than 5 respiratory infections that occurred during the 12 months prior to the beginning of the study. Children were randomised into an active group, treated with Imunoglukan P4H® syrup (with pleuran-β-glucan from Pleurotus ostreatus and vitamin C), or a placebo group (vitamin C only). During the 3 visits, within a 12-month period, questionnaires were completed, and blood samples were examined for immune parameters.

RESULTS

In the active group, 36% of the children did not suffer from any respiratory infections throughout the treatment, compared to 21% in the placebo group (p<0.05). Imunoglukan P4H® also significantly decreased the frequency of flu and flu-like disease and the number of lower respiratory tract infections. Imunoglukan P4H® treatment resulted in a statistically significant modulation of humoral and cellular immunity.

CONCLUSIONS

Results from this study demonstrate that Imunoglukan P4H® is effective in the prevention of RRTIs in children. Furthermore, our results also revealed complex immunomodulatory activity of this product. This is the first double-blind, placebo-controlled study in children with RRTIs that has addressed the preventive effects of pleuran on morbidity caused by respiratory infections.

Polypodium leucotomos Extract use to prevent and reduce the risk of infectious diseases in high performance athletes

Objective

Many components of the immune system undergo adverse changes during intense physical activity in athletes, leading to a heightened risk of respiratory tract infections. This study evaluated the reduction in infectious processes in athletes due to intensive training with anapsos.

Methods

The study compared athletes who took 480 mg Polypodium leucotomos Extract (Armaya fuerte; Centrum laboratories, Alicante, Spain) twice daily for 3 months (n = 50) with a control group (n = 50) in the evaluation of the onset of infectious processes and relapses during an 8-month period (June 2010 to January 2011).

Results

The onset of infectious processes in the Polypodium leucotomos Extract group was lower when compared to the control group (14% versus 56%). Relapse in the Polypodium leucotomos Extract group was seen in just one athlete (14.2%) compared to ten athletes (37.5%) in the control group.

Conclusion

Polypodium leucotomos Extract has been shown to be useful in the prevention of infectious processes, as well as reducing recurring episodes in athletes.

Exercise-induced immunodepression in endurance athletes and nutritional intervention with carbohydrate, protein and fat-what is possible, what is not?

Heavily exercising endurance athletes experience extreme physiologic stress, which is associated with temporary immunodepression and higher risk of infection, particularly upper respiratory tract infections (URTI). The aim of this review is to provide a critical up-to-date review of existing evidence on the immunomodulatory potential of selected macronutrients and to evaluate their efficacy. The results of 66 placebo-controlled and/or crossover trials were compared and analysed. Among macronutrients, the most effective approach to maintain immune function in athletes is to consume ≥6% carbohydrate during prolonged exercise. Because inadequate nutrition affects almost all aspects of the immune system, a well-balanced diet is also important. Evidence of beneficial effects from other macronutrients is scarce and results are often inconsistent. Using a single nutrient may not be as effective as a mixture of several nutritional supplements. Due to limited research evidence, with the exception of carbohydrate, no explicit recommendations to reduce post-exercise URTI symptoms with single macronutrients can be derived.

Emerging supplements in sports

CONTEXT

Nutritional supplements advertised as ergogenic are commonly used by athletes at all levels. Health care professionals have an opportunity and responsibility to counsel athletes concerning the safety and efficacy of supplements on the market.

EVIDENCE ACQUISITION

An Internet search of common fitness and bodybuilding sites was performed to identify supplement promotions. A search of MEDLINE (2000-August, 2011) was performed using the most commonly identified supplements, including glutamine, choline, methoxyisoflavone, quercetin, zinc/magnesium aspartate, and nitric oxide. The search terms supplement, ergogenic aid, and performance were also used.

RESULTS

Six common and newer supplements were identified, including glutamine, choline, methoxyisoflavone, quercetin, zinc/magnesium aspartate, and nitric oxide.

CONCLUSIONS

Controlled studies have not determined the effects of these supplements on performance in athletes. Scientific evidence is not available to support the use of these supplements for performance enhancement.

Pleuran (β-glucan from Pleurotus ostreatus) supplementation, cellular immune response and respiratory tract infections in athletes

Prolonged and exhausting physical activity causes numerous changes in immunity and sometimes transient increases the risk of upper respiratory tract infections (URTIs). Nutritional supplements as countermeasures to exercise-induced changes have increasingly been studied in the last decade. One of the most promising nutritional supplements is β-glucan, a well-known immunomodulator with positive effects on the function of immunocompetent cells. In this double blind, placebo-controlled study, we investigated the effect of pleuran, an insoluble β-(1,3/1,6) glucan from mushroom Pleurotus ostreatus, on selected cellular immune responses and incidence of URTI symptoms in athletes. Fifty athletes were randomized to pleuran or placebo group, taking pleuran (commercial name Imunoglukan(®)) or placebo supplements during 3 months. Venous whole blood was collected before and after 3 months of supplementation and additionally 3 months after supplementation period was completed. Incidence of URTI symptoms together with characterization of changes in phagocytosis and natural killer (NK) cell count was monitored during the study. We found that pleuran significantly reduced the incidence of URTI symptoms and increased the number of circulating NK cells. In addition, the phagocytosis process remained stable in pleuran group during the study in contrast to placebo group where significant reduction of phagocytosis was observed. These findings indicate that pleuran may serve as an effective nutritional supplement for athletes under heavy physical training. Additional research is needed to determine the mechanisms of pleuran function.

Physical activity, immunity and infection

During the last few decades, scientific evidence has confirmed a wide range of health benefits related to regular physical activity. How physical activity affects the immune function and infection risk is, however, still under debate. Commonly, intensive exercise suppresses the activity and levels of several immune cells, while other immune functions may be stimulated by moderate physical activity. With this knowledge, the understanding of the relationship between different levels of physical activity on the immune function has been raised as a potential tool to protect health not only in athletes but also in the general population; the mechanisms that translate a physically active lifestyle into good health continue to be investigated. Reviewing the literature, although several outcomes (i.e. the mechanisms by which different levels and duration of physical activity programmes affect numerous cell types and responses) remain unclear, given that the additional benefits encompass healthy habits including exercise, the use of physical activity programmes may result in improved health of elderly populations. Moderate physical activity or moderate-regulated training may enhance the immune function mainly in less fit subjects or sedentary population and the pre-event fitness status also seems to be an important individual factor regarding this relationship. Although adequate nutrition and regular physical activity habits may synergistically improve health, clinical trials in athletes using nutritional supplements to counteract the immune suppression have been inconclusive so far.Further research is necessary to find out to what extent physical activity training can exert an effect on the immune function.

Immune-modulating efficacy of a polyphenol-rich beverage on symptoms associated with the common cold: a double-blind, randomised, placebo-controlled, multi-centric clinical study

In the present study, the immune-modulating efficacy of a polyphenol-rich beverage on symptoms associated with the common cold was evaluated. For this purpose, ninety-eight patients reporting common cold symptoms that began no longer than 24 h before the study intervention were randomly assigned to consume either the test beverage or placebo twice per d for 10 d. The severity of the disease was expressed as the total score of the five cold symptoms 'general feeling of sickness', 'headache and/or joint aches', 'sore throat and/or difficulty swallowing', 'hoarseness and/or cough' and 'stuffy nose/sniffle'. Consequently, the decrease from 10.2 (sd 3.1) points at the beginning to 2.1 (sd 2.7) points by the end of the study in the verum group demonstrated a clear improvement, whereas in the placebo group only a reduction from 10.5 (sd 3.0) to 6.3 (sd 3.8) points could be observed. The mean difference between the groups (primary efficacy criterion) of 3.9 points was highly significant (P < 0.01). At the end of the study there were highly significantly (P < 0.01) more patients in the verum group complaint free than in the placebo group (secondary efficacy criterion). In addition to these self-reported values, several local findings of the physical examination were also significantly improved in the verum group.

Effects of supplementation with free glutamine and the dipeptide alanyl-glutamine on parameters of muscle damage and inflammation in rats submitted to prolonged exercise

In this study, we investigated the effect of the supplementation with the dipeptide L-alanyl-L-glutamine (DIP) and a solution containing L-glutamine and L-alanine on plasma levels markers of muscle damage and levels of pro-inflammatory cytokines and glutamine metabolism in rats submitted to prolonged exercise. Rats were submitted to sessions of swim training for 6 weeks. Twenty-one days prior to euthanasia, the animals were supplemented with DIP (n = 8) (1.5 g.kg(-1)), a solution of free L-glutamine (1 g.kg(-1)) and free L-alanine (0.61 g.kg(-1)) (G&A, n = 8) or water (control (CON), n = 8). Animals were killed at rest before (R), after prolonged exercise (PE-2 h of exercise). Plasma concentrations of glutamine, glutamate, tumour necrosis factor-alpha (TNF-alpha), prostaglandin E2 (PGE2) and activity of creatine kinase (CK), lactate dehydrogenase (LDH) and muscle concentrations of glutamine and glutamate were measured. The concentrations of plasma TNF-alpha, PGE2 and the activity of CK were lower in the G&A-R and DIP-R groups, compared to the CON-R. Glutamine in plasma (p < 0.04) and soleus muscle (p < 0.001) was higher in the DIP-R and G&A-R groups relative to the CON-R group. G&A-PE and DIP-PE groups exhibited lower concentrations of plasma PGE2 (p < 0.05) and TNF-alpha (p < 0.05), and higher concentrations of glutamine and glutamate in soleus (p < 0.001) and gastrocnemius muscles (p < 0.05) relative to the CON-PE group. We concluded that supplementation with free L-glutamine and the dipeptide LL-alanyl-LL-glutamine represents an effective source of glutamine, which may attenuate inflammation biomarkers after periods of training and plasma levels of CK and the inflammatory response induced by prolonged exercise.

Effect of physical activity on glutamine metabolism

PURPOSE OF REVIEW

Glutamine is largely synthesized in skeletal muscles and provides fuel to rapidly dividing cells of the immune system and precursors to gluconeogenesis in the liver. Physical exercise is known to affect glutamine synthesis and to modulate glutamine uptake. Overtraining is frequently associated with reduced availability of glutamine and decreased immunocompetence. Inactivity affects glutamine metabolism, but this subject was poorly investigated.

RECENT FINDINGS

Strenuous physical exercise as well as exhaustive training programs lead to glutamine depletion due to lowered synthesis and enhanced uptake by liver and immune cells. Evidence suggests that postexercise glutamine depletion is associated with immunodepression. Counterwise, moderate training leads to improved glutamine availability due to a positive balance between muscle synthesis and peripheral clearance. Physical inactivity, as investigated by experimental bed rest in healthy volunteers, reduced glutamine synthesis and availability.

SUMMARY

After exercise, a reduced glutamine availability may be considered as a marker of overtraining. An increased glutamine availability may contribute to decreased inflammation and health benefits associated with optimal training. Thus, glutamine supplementation may enhance immunocompetence after strenuous exercise. The potential of glutamine supplementation during physical inactivity needs to be explored.

Glutamina: aspectos bioquímicos, metabólicos, moleculares e suplementação

A glutamina é o aminoácido livre mais abundante no plasma e no tecido muscular. Nutricionalmente é classificada como um aminoácido não essencial, uma vez que pode ser sintetizada pelo organismo a partir de outros aminoácidos. A glutamina está envolvida em diferentes funções, tais como a proliferação e desenvolvimento de células, o balanço acidobásico, o transporte da amônia entre os tecidos, a doação de esqueletos de carbono para a gliconeogênese, a participação no sistema antioxidante e outras. Por meio de técnicas de biologia molecular, estudos demonstram que a glutamina pode também influenciar diversas vias de sinalização celular, em especial a expressão de proteínas de choque térmico (HSPs). As HSPs contribuem para a manutenção da homeostasia da célula na presença de agentes estressores, tais como as espécies reativas de oxigênio (ERO). Em situações de elevado catabolismo muscular, como após exercícios físicos intensos e prolongados, a concentração de glutamina pode tornar-se reduzida. A menor disponibilidade desse aminoácido pode diminuir a resistência da célula a lesões, levando a processos de apoptose celular. Por essas razões, a suplementação com L-glutamina, tanto na forma livre, quanto como dipeptídeo, tem sido investigada. Alguns aspectos bioquímicos, metabólicos e mecanismos moleculares da glutamina, bem como os efeitos de sua suplementação, são abordados no presente trabalho.

Effects of squat exercise and branched-chain amino acid supplementation on plasma free amino acid concentrations in young women

The present study was conducted to examine alterations in plasma free amino acid concentrations induced by squat exercise and branched-chain amino acid (BCAA) supplementation in young, untrained female subjects. In the morning on the exercise session day, participants ingested drinks containing either BCAA (isoleucine:leucine:valine=1:2.3:1.2) or dextrin (placebo) at 0.1 g/kg body weight 15 min before a squat exercise session, which consisted of 7 sets of 20 squats, with 3 min intervals between sets. In the placebo trial, plasma BCAA concentrations were decreased subsequent to exercise, whereas they were significantly increased in the BCAA trial until 2 h after exercise. Marked changes in other free amino acids in response to squat exercise and BCAA supplementation were observed. In particular, plasma concentrations of methionine and aromatic amino acids were temporarily decreased in the BCAA trial, being significantly lower than those in the placebo trial. These results suggest that BCAA intake before exercise affects methionine and aromatic amino acid metabolism.

Reporting of systematic reviews of micronutrients and health: a critical appraisal

BACKGROUND

The quality of nutrition-related systematic reviews (SRs) is an unstudied but important factor affecting their usefulness.

OBJECTIVES

The objectives were to evaluate the reporting quality of published SRs and to identify areas of improvement.

DESIGN

Descriptive and exploratory analyses of the reporting quality (7 nutrition items and 28 SR reporting items) of all English-language SRs published through July 2007 linking micronutrients and health outcomes in humans were conducted. Factors that may be associated with reporting quality were also evaluated.

RESULTS

We identified 141 eligible SRs of 21 micronutrients. Ninety SRs that included only interventional studies met a higher proportion of our reporting criteria (median: 62%; interquartile range: 51%, 72%) than did 31 SRs with only observational studies (median: 53%; interquartile range: 47%, 60%) or 20 SRs with both study designs (median: 47%; interquartile range: 39%, 52%) (P < 0.001). SRs published after consensus reporting standards (since 2003) met a higher proportion of the reporting criteria than did earlier SRs (median: 59% compared with 50%; P = 0.01); however, the reporting of nutrition variables remained unchanged (median: 38% compared with 33%; P = 0.7). The least-reported nutrition criteria were baseline nutrient exposures (28%) and effects of measurement errors from nutrition exposures (24%). Only 58 SRs (41%) used quality scales or checklists to assess the methodologic quality of the primary studies included.

CONCLUSIONS

The reporting quality of SRs has improved 3 y after publication of SR reporting standards, but the reporting of nutrition variables has not. Improved adherence to consensus methods and reporting standards should improve the utility of nutrition SRs.

Does physical exercise modify antioxidant requirements?

Physical training is known to induce a biochemical adaptive response which might require an increase in the ingestion and/or the absorption of micronutrients. A question that is still being raised is whether acute or chronic exercise modifies antioxidant requirements. First, the present review brings to light the most crucial studies on the topic. Second, it interprets the established relationships between antioxidant micronutrient intakes and the adaptive response of antioxidant systems. Finally, it exposes the major questions connected with antioxidant micronutrient requirements for athletes. To this effect, the training-load interaction with nutrition is taken into account. As oxidative stress cannot be avoided, the imbalance between oxidants and antioxidants can be alleviated to minimise oxidative damage and outcomes. There is growing evidence that one specific antioxidant cannot by itself prevent oxidative stress-induced damage, as direct adverse effects of supplementation are attributed to undesirable synergic effects. Other effects can be supposed that limit the endogenous adaptive effect of training. High doses of antioxidant supplements can minimise the effects of radical oxygen species themselves or generate pro-oxidant effects. Effects are only exhibited when nutritional status is deficient. There are no convincing effects of supplementation in well-trained athletes. Risk/benefit analysis emerges on evidence for an unknown risk of supranutritional intakes, a supposed impairment of adaptive effects and a still unknown long-term risk. Appropriate status can be achieved by a diversified and balanced diet, adapted to specific needs, by awareness of high-density food intakes (avoiding products containing a low density of micronutrients).

Does exercise increase the risk of upper respiratory tract infections?

INTRODUCTION OR BACKGROUND

Heavy exercise induces marked immunodepression, which is multifactorial in origin. Evidence showing clinical significance of this immunodepression is scarce.

SOURCES OF DATA

We assessed in a systematic manner whether physical activity or intensity of exercise increase susceptibility to upper respiratory tract infections (URTI). A literature search was performed using the keywords 'upper respiratory tract infections', 'athletes', 'exercise' and 'physical activity'. We considered all studies reporting of the effect of exercise, physical activity, sport and training on susceptibility to URTI. A total of 162 publications were identified and 30 studies were eligible (4 descriptive, 18 observational and 8 interventional). The 30 studies included 8595 athletes (5471 runners, 2803 swimmers) and 1798 non-athletes.

AREAS OF AGREEMENT

Moderate activity may enhance immune function, whereas prolonged, high-intensity exercise temporarily impairs the immune competence. Athletes, when compared with lesser active individuals, experience higher rate of URTI after training and competitions. In non-athletes, increasing physical activity is associated with a decreased risk of URTI.

AREAS OF CONTROVERSY

The relationship between exercise and URTI is affected by poorly known individual determinants such as genetic factors, fitness, nutritional status or atopy. Elite athletes may have a decreased susceptibility to URTI.

GROWING POINTS AND AREAS TIMELY FOR DEVELOPING RESEARCH

The dose-response relationship between immunodepression and risk for URTI during the weeks following heavy exercise. What are the clinically relevant methods to assess exercise-induced immunodepression? Is down-regulation of immunity after intense exercise a protective response to limit inflammation? Is there a role for nutritional or pharmaceutical interventions to reduce risk of URTI?

Quercetin reduces susceptibility to influenza infection following stressful exercise

Exercise stress is associated with increased risk for upper respiratory tract infection. We have shown that exercise stress can increase susceptibility to infection. Quercetin, a flavonoid present in a wide variety of fruits and vegetables, has been reported to inhibit infectivity and replication of a broad spectrum of viruses and may offset the increase in susceptibility to infection associated with stressful exercise. This study examined the effects of quercetin feedings on susceptibility to the influenza virus A/Puerto Rico/8/34 (H1N1) following stressful exercise. Mice were randomly assigned to one of four treatment groups: exercise-placebo, exercise-quercetin, control-placebo, or control-quercetin. Exercise consisted of a run to fatigue (approximately 140 min) on a treadmill for 3 consecutive days. Quercetin (12.5 mg/kg) was administered via gavage for 7 days before viral challenge. At 30 min after the last bout of exercise or rest, mice (n=23-30) were intranasally inoculated with a standardized dose of influenza virus (0.04 hemagglutinating units). Mice were monitored daily for morbidity (time to sickness), symptom severity, and mortality (time to death) for 21 days. Exercise stress was associated with an increased susceptibility to infection [morbidity, mortality, and symptom severity on days 5-7 (P<0.05)]; quercetin offset the increase in susceptibility to infection [morbidity, mortality, and symptom severity on days 5-7 (P<0.05)] that was associated with stressful exercise. These data suggest that short-term quercetin feedings may prove to be an effective strategy to lessen the impact of stressful exercise on susceptibility to respiratory infection.

Mechanisms of asthma in Olympic athletes--practical implications

Athletes' symptoms may only occur in extreme conditions, which are far from normal. Exercise may increase ventilation up to 200 l/min for short periods in speed and power athletes, and for longer periods in endurance athletes such as swimmers and cross-country skiers. Increasing proportions of young athletes are atopic, i.e. they show signs of IgE-mediated allergy which is, along with the sport event (endurance sport), a major risk factor for asthma and respiratory symptoms. Mechanisms in the etiology and clinical phenotypes vary between disciplines and individuals, and it may be an oversimplification to discuss athlete's asthma as a distinct and unambiguous disease. Nevertheless, the experience on Finnish Olympic athletes suggests at least two different clinical phenotypes, which may reflect different underlying mechanisms. The pattern of 'classical asthma' is characterized by early onset childhood asthma, methacholine responsiveness, atopy and signs of eosinophilic airway inflammation, reflected by increased exhaled nitric oxide levels. Another distinct phenotype includes late onset symptoms (during sports career), bronchial responsiveness to eucapnic hyperventilation test, but not necessarily to inhaled methacholine, and a variable association with atopic markers and nitric oxide. A mixed type of eosinophilic and neutrophilic airway inflammation seems to affect especially swimmers, ice-hockey players, and cross-country skiers. The inflammation may represent a multifactorial trauma, in which both allergic and irritant mechanisms play a role. There is a significant problem of both under- and overdiagnosing asthma in athletes and the need for objective testing is emphasized. Follow-up studies are needed to assess the temporal relationship between asthma and competitive sporting, taking better into account individual disposition, environmental factors (exposure), intensity of training and potential confounders.

Effects of the fish-oil supplementation on the immune and inflammatory responses in elite swimmers

The effect of fish-oil supplementation (FO-S) on the immune responses of elite swimmers was investigated. In a randomized placebo-controlled trial, swimmers received either fish-oil capsules (n=10) containing long chain polyunsaturated fatty acids (FA) of n-3 (LCPUFA n-3) or placebo capsules (n=10), both for 6 weeks. Plasma FA, immunological markers, insulin and cortisol were evaluated. The FO-S resulted in an increase in LCPUFA n-3 and a decrease in arachidonic n-6 FA in plasma and a reduction in the production of interferon-gamma by cultured cells. A reduction in the production of tumor necrosis factor-alpha was observed in both groups. An increase in interleukin-2 production and no significant difference in interleukin-4 were also observed. FO-S was able to attenuate the exercise-induced increases in prostaglandin E2. Circulating concentrations of insulin did not change, while cortisol and glucose showed increase after the study period. These results suggest that FO-S influence exercise-associated immune responses in competitive swimmers.

Glutamine: the nonessential amino acid for performance enhancement

Glutamine is a popular dietary supplement consumed for purported ergogenic benefits of increased strength, quicker recovery, decreased frequency of respiratory infections, and prevention of overtraining. From a biochemical standpoint, glutamine does play a physiologic role in each of these areas, but it remains only one of a host of factors involved. This review examines the effects of glutamine on exercise and demonstrates a lack of evidence for definitive positive ergogenic benefits as a result of glutamine supplementation.