Hormonal contraception for female athletes presents special needs and concerns.

PURPOSE: Oral contraceptives (OCs) are commonly used by female athletes raising concerns regarding the possible adverse effects of OCs on physical performance, musculoskeletal injuries, and bone density. We aimed to review all current studies on the physiological effects of OCs in physically active women. MATERIALS AND METHODS: A review of literature in electronic search in PubMed and Google Scholar databases from December 2002 to December 2022 using relevant keywords. The reference lists of the articles found eligible were also reviewed. RESULTS: Out of 344 articles in the initial database, 54 clinical studies were eligible for inclusion in our literature review. OCs are used by about two-thirds of female athletes. Current research suggests that OCs' effects on endurance performance and muscle strength are mostly reassuring. OCs do not seem to have a major negative impact on bone health or sports injuries. In fact, new data suggests that they may even significantly reduce the risk of anterior cruciate ligament (ACL) injury. CONCLUSIONS: OCs can be safely used by young female athletes, who may also benefit from better menstrual cycle control. OCs offer newly realised protection from ACL injuries. The use of OCs must be carefully individualised according to their preferences, expectations, and experience.

Hormonal contraception can be safely prescribed to active women. The International Olympic Committee advocates a new and wider definition for the 'athlete triad', where low energy availability presents a special challenge for these athletes. New data suggests that the use of oral contraceptives may protect against ACL injury.

Primary, secondary and tertiary prevention of Relative Energy Deficiency in Sport (REDs): a narrative review by a subgroup of the IOC consensus on REDs.

Relative Energy Deficiency in Sport (REDs) is common among female and male athletes representing various sports at different performance levels, and the underlying cause is problematic low energy availability (LEA). It is essential to prevent problematic LEA to decrease the risk of serious health and performance consequences. This narrative review addresses REDs primary, secondary and tertiary prevention strategies and recommends best practice prevention guidelines targeting the athlete health and performance team, athlete entourage (eg, coaches, parents, managers) and sport organisations. Primary prevention of REDs seeks to minimise exposure to and reduce behaviours associated with problematic LEA. Some of the important strategies are educational initiatives and de-emphasising body weight and leanness, particularly in young and subelite athletes. Secondary prevention encourages the early identification and management of REDs signs or symptoms to facilitate early treatment to prevent development of more serious REDs outcomes. Recommended strategies for identifying athletes at risk are self-reported screening instruments, individual health interviews and/or objective assessment of REDs markers. Tertiary prevention (clinical treatment) seeks to limit short-term and long-term severe health consequences of REDs. The cornerstone of tertiary prevention is identifying the source of and treating problematic LEA. Best practice guidelines to prevent REDs and related consequences include a multipronged approach targeting the athlete health and performance team, the athlete entourage and sport organisations, who all need to ensure a supportive and safe sporting environment, have sufficient REDs knowledge and remain observant for the early signs and symptoms of REDs.

Best practice recommendations for body composition considerations in sport to reduce health and performance risks: a critical review, original survey and expert opinion by a subgroup of the IOC consensus on Relative Energy Deficiency in Sport (REDs).

BACKGROUND: The assessment of body composition (BC) in sport raises concern for athlete health, especially where an overfocus on being lighter or leaner increases the risk of Relative Energy Deficiency in Sport (REDs) and disordered eating. METHODS: We undertook a critical review of the effect of BC on performance (29 longitudinal, prospective or intervention studies) and explored current practice related to BC considerations via a follow-up to a 2013 internationally distributed survey. RESULTS: The review found that a higher level of body fat was negatively associated with endurance performance, while a gain in muscle mass resulted in performance benefits across sports. BC did not contribute to early talent identification, and no unique cut-off to signify a performance advantage for BC was identified. BC appears to be one of an array of variables impacting performance, and its influence should not be overstated. The survey (125 practitioners, 61 sports and 26 countries) showed subtle changes in BC considerations over time, such as an increased role for sport dietitian/nutrition practitioners as BC measurers (2013: 54%, 2022: 78%); less emphasis on reporting of body fat percentage (2013: 68%, 2022: 46%) and reduced frequency of BC assessment if ≥every fourth week (2013: 18%, 2022: 5%). Respondents remained concerned about a problematic focus on BC (2013: 69%, 2022: 78%). To address these findings, we provide detailed recommendations for BC considerations, including an overview of preferable BC methodology. CONCLUSIONS: The 'best practice' guidelines stress the importance of a multidisciplinary athlete health and performance team, and the treatment of BC data as confidential medical information. The guidelines provide a health focus around BC, aiming to reduce the associated burden of disordered eating, problematic low energy availability and REDs.

2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs).

Relative Energy Deficiency in Sport (REDs) was first introduced in 2014 by the International Olympic Committee's expert writing panel, identifying a syndrome of deleterious health and performance outcomes experienced by female and male athletes exposed to low energy availability (LEA; inadequate energy intake in relation to exercise energy expenditure). Since the 2018 REDs consensus, there have been >170 original research publications advancing the field of REDs science, including emerging data demonstrating the growing role of low carbohydrate availability, further evidence of the interplay between mental health and REDs and more data elucidating the impact of LEA in males. Our knowledge of REDs signs and symptoms has resulted in updated Health and Performance Conceptual Models and the development of a novel Physiological Model. This Physiological Model is designed to demonstrate the complexity of either problematic or adaptable LEA exposure, coupled with individual moderating factors, leading to changes in health and performance outcomes. Guidelines for safe and effective body composition assessment to help prevent REDs are also outlined. A new REDs Clinical Assessment Tool-Version 2 is introduced to facilitate the detection and clinical diagnosis of REDs based on accumulated severity and risk stratification, with associated training and competition recommendations. Prevention and treatment principles of REDs are presented to encourage best practices for sports organisations and clinicians. Finally, methodological best practices for REDs research are outlined to stimulate future high-quality research to address important knowledge gaps.

[PHYSICAL ACTIVITY DURING PREGNANCY AND AFTER BIRTH].

INTRODUCTION: Physical activity (PA) decreases morbidity, improves quality of life and elongates life span. PA during pregnancy is safe and decreases complications. Physical inactivity during pregnancy is an independent risk factor for maternal weight gain and complications. Pregnancy is a golden opportunity to promote a healthy lifestyle. OBJECTIVES: This article aims to review the latest recommendations regarding PA in pregnancy. In this article we focused on the following: The joint guidelines of the Society of Obstetricians and Gynaecologists of Canada's (SOGC) and the Canadian Society for Exercise Physiology (CSEP), the American College of Obstetricians and Gynecologists (ACOG) committee opinion, and the ACSM's (American College of Sports Medicine) Guidelines for Exercise Testing and Prescription, the 11th Edition published in 2019, 2020 and 2022 respectively. CONCLUSIONS: PA during pregnancy is safe and essential. Every pregnant woman without contraindications should perform 150 weekly minutes of aerobic exercise and resistance training. DISCUSSION: A weekly goal of 150 medium intensity aerobic exercise minutes spread over at least 3 separate days combined with resistance training is recommended for every pregnant woman, including women who were inactive prior to the pregnancy, those diagnosed with gestational diabetes and overweight or obese women. Pregnant women with absolute contraindication can continue to perform their daily activities but avoid more intense activities, those with relative contraindications should discuss the advantages and risks of PA with their attending physician. After birth, women can return to PA gradually depending on the mode of delivery and complications encountered.

Correction: AVPR1a and SLC6A4 Gene Polymorphisms Are Associated with Creative Dance Performance.

[This corrects the article DOI: 10.1371/journal.pgen.0010042.].

Rare Cause of Syncope in an Athlete, Matter of Brain and Heart Electricity.

ABSTRACT: A 17-year-old elite triathlete presented with recurrent loss of consciousness events. Implantable loop recorder (ILR) documented sinus node asystoles of up to 21 seconds. She underwent cardiac neuromodulation ablation. After ablation, a generalized tonic-clonic seizure (GTCS) occurred, without concomitant asystole on the ILR. Temporal lobe seizures were diagnosed and supported by interictal epileptic activity on electroencephalogram. We assumed that the syncope episodes were ictal asystole (IA) and that the IA terminated the epileptic seizures early after their onset. The cardiac ablation prevented IA, enabling spread of seizure activity and development of GTCS. To the best of our knowledge, this is the first case of IA treated with cardiac ablation, allowing avoidance of cardiac pacing. This case raises the awareness to epileptic seizures as a cause of asystole in athletes, with an elusive and atypical presentation.

[RECOMMENDATIONS FOR CHANGING CARDIOVASCULAR SCREENING OF ATHLETES WHO ARE REQUIRED FOR PRE-PARTICIPATION SCREENING UNDER THE SPORTS LAW - A POSITION PAPER ON BEHALF OF THE ISRAEL HEART SOCIETY].

INTRODUCTION: For many years routine screening of athletes in Israel includes frequently performed ECGs and exercise tests that overload the system with questionable benefits. The purpose of the current document is to reevaluate the need for pre-participation testing and establish new evidence-based guidelines. It should be noted that our proposal for a change of approach relates only to subjects whose health questionnaire is normal, who do not have a family history of sudden and unexpected death at an early age, or a family history of hereditary heart disease and whose physical examination from a cardiovascular point of view is normal.

Myokine levels after resistance exercise in young adults with Prader-Willi syndrome (PWS).

Individuals with PWS require marked caloric restriction and daily exercise to prevent morbid obesity. Lower energy expenditure, hypotonia, decreased muscle mass, and cognitive impairment make exercise challenging for this population. Exercise guidelines include resistance training as an important component. Myokine responses to resistance exercise may mediate beneficial metabolic effects. We aimed to determine if young PWS adults can perform a resistance exercise program and to measure myokine responses in PWS versus age- and BMI-matched controls. Each group included 11 participants (7M/4F). Ages and BMI for PWS and controls were 30.7 ± 4.6 versus 30.1 ± 4.3 years and 28.3 ± 4.3 versus 28.2 ± 4.2 kg/m2 , respectively. Glucose, creatine kinase (CK), lactate, and myokines were measured before, after, 30, and 60 min after completing eight resistance exercises. Myokines were assayed using a multiplex myokine panel (Merck Millipore). CK was lower in PWS versus controls (62 ± 16 vs.322 ± 100 U/L, p < .04). Peak lactate was 3.7 ± 0.7 in PWS versus 7.3 ± 0.7 mmol/Lin controls (p < .001). The increase in interleukin-6 was similar in PWS and controls (41 ± 16% and 35 ± 10%, respectively). Pre- and post-exercise levels of the six myokines assayed showed no consistent differences between the PWS and control participants. PWS young adults are capable of performing resistance/strength-building exercise. The lower CK and peak lactate levels in PWS may reflect decreased muscle mass in this population. Further studies are needed to determine optimal exercise regimens and assess the role of myokines incontributing to the metabolic phenotype of PWS.

Physical activity and maximal oxygen uptake in adults with Prader-Willi syndrome.

BACKGROUND: Prader-Willi Syndrome (PWS) is the most common genetic syndrome causing life-threatening obesity. Strict adherence to a low-calorie diet and regular physical activity are needed to prevent weight gain. Direct measurement of maximal oxygen uptake (VO2 max), the "gold standard" for assessing aerobic exercise capacity, has not been previously described in PWS. OBJECTIVES: Assess aerobic capacity by direct measurement of VO2 max in adults with PWS, and in age and BMI-matched controls (OC), and compare the results with values obtained by indirect prediction methods. METHODS AND PATIENTS: Seventeen individuals (12 males) age: 19-35 (28.6 ± 4.9) years, BMI: 19.4-38.1 (27.8 ± 5) kg/m2 with genetically confirmed PWS who exercise daily, and 32 matched OC (22 males) age: 19-36 (29.3 ± 5.2) years, BMI: 21.1-48.1 (26.3 ± 4.9) kg/m2. All completed a medical questionnaire and performed strength and flexibility tests. VO2 max was determined by measuring oxygen consumption during a graded exercise test on a treadmill. RESULTS: VO2 max (24.6 ± 3.4 vs 46.5 ± 12.2 ml/kg/min, p < 0.001) and ventilatory threshold (20 ± 2 and 36.2 ± 10.5 ml/kg/min, p < 0.001), maximal strength of both hands (36 ± 4 vs 91.4 ± 21.2 kg, p < 0.001), and flexibility (15.2 ± 9.5 vs 26 ± 11.1 cm, p = 0.001) were all significantly lower for PWS compared to OC. Predicted estimates and direct measurements of VO2 max were almost identical for the OC group (p = 0.995), for the PWS group, both methods for estimating VO2 max gave values which were significantly greater (p < 0.001) than results obtained by direct measurements. CONCLUSIONS: Aerobic capacity, assessed by direct measurement of VO2 max, is significantly lower in PWS adults, even in those who exercise daily, compared to OCs. Indirect estimates of VO2 max are accurate for OC, but unreliable in PWS. Direct measurement of VO2 should be used for designing personal training programs and in clinical studies of exercise in PWS.

[A PARADIGM SHIFT IN THE PERCEPTION OF HEALTH MAINTENANCE FROM INCREASING PHYSICAL ACTIVITY TO DECREASING PHYSICAL INACTIVITY].

Modern man spends most of his waking hours (50-70%) in one form or another of sedentary behavior, defined as activity conducted in a sitting or reclining position involving low energy expenditure. The remaining waking hours are spent performing low intensity physical activity (25-45%) and medium-high intensity physical activity (less than 5%): Despite this distribution, medical research has focused on the impact of increasing medium-high intensity physical activity and many health organizations' recommendations are in accordance. In recent years, research conducted has begun to examine the effect inactivity has on health and has shown that excess sedentary behaviour is an independent risk factor for a wide range of medical problems such as obesity, metabolic syndrome, poor cardiovascular health profile, diabetes mellitus, and possibly cancer. Although the higher risk brought on by sedentary behaviour is partially reduced by increasing medium-high intensity physical activity, it is not completely neutralized. One way to diminish the harm caused by long hours of sitting is to take short breaks during periods of prolonged sitting in order to walk. According to these findings, it is worthwhile to recommend reducing the hours spent in sedentary behaviour, or at least to take frequent short breaks ("activity snacks") during periods of prolonged sitting to get up and walk around.

[SPORT MEDICINE].

Sports Medicine is a relatively new subject in medicine and includes a variety of medical and paramedical fields. Although sports medicine is mistakenly thought to be mainly for sports professionals/athletes, it actually encompasses the entire population, including the active and non-active healthy populations, as well as the sick. Sports medicine also engages amateur sportsmen and strives to promote physical activity and quality of life in the general population. Hence, the field involves all ages from childhood to old age, aiming to preserve and support every person at every age. Sports medicine, which started developing in the 19th century, is today a specialty, primary or secondary, in many countries, while in others it is a fellowship or under the jurisdiction of local or sports authorities. In Israel, the field exists since the 1950's and is advanced. The Sports Medicine Society founded a 3-year course of continued education in sport medicine as part of the Tel-Aviv University Faculty of Medicine. Later on, a fellowship in general Sports Medicine and in Orthopedic Sports Medicine were developed within the Israel Medical Association. A year ago, Israel formally became a member of the global "Exercise is Medicine" foundation, and under this title promotes education for health care providers on exercise prescription. The understanding of the importance of physical activity and fitness as part of a healthy lifestyle is increasing in Israel, as well as the number of amateur athletes, and the profession of sports medicine takes a big part in this process.

[ATHLETE'S HEART - THE MORE THE MERRIER?]

INTRODUCTION: Regular moderate exercise training is effective for the prevention and treatment of many common chronic diseases and improves cardiovascular health and life expectancy. However, long-term excessive endurance exercise may induce pathological structural remodeling of the heart. The athlete's heart is characterized by enlargement of cardiac chambers and eccentric hypertrophy with preserved myocardial function as normal physiological adaptations for prolonged and intense endurance physical stress. However, recent studies have demonstrated transient right ventricular dysfunction and elevation of cardiac biomarkers following intense endurance exercise. Repeated bouts of acute stress may cause patchy fibrosis of the right heart and interventricular septum, creating an arrhythmogenic substrate. The following review summarizes the current medical literature on the effects of intense and prolonged endurance exercise on cardiac structure and function and its clinical significance.

[EXERCISE CAPACITY AND AEROBIC PHYSICAL FITNESS ASSESSMENT AMONG ADOLESCENTS AND ADULTS WITH CYSTIC FIBROSIS BY A QUESTIONNAIRE AND EXERCISE TESTS].

BACKGROUND: Physical exercise has been shown to improve lung condition or to slow deterioration in patients with cystic fibrosis (CF) and improves their quality of life. This study analyzes the physical exercise capacity and the level of aerobic fitness of adolescents and adults with CF who are patients at the CF Center at Hadassah Medical Center Mount Scopus in Jerusalem, Israel. OBJECTIVES: To assess physical exercise capacity and aerobic capacity levels among CF patients by a physical activity questionnaire in comparison to assessment by exercise tests. METHODS: The participants completed a physical activity questionnaire, performed the "6 minute walk test" and a cardio-pulmonary test on a treadmill. RESULTS: The study group included 36 patients, ages 12-43 years, who completed a physical activity questionnaire. Most patients (92%) reported engaging in physical exercise. Most of those who exercised (61%) did so at a low intensity, as described in CF research literature. The average weekly exercise time was 177 minutes; 35 patients completed a cardio-pulmonary exercise test and a "6 minute walk test". The cardio-pulmonary exercise tests showed that 34% of the participants had 'good to excellent' aerobic fitness, 26% had 'moderate' aerobic fitness and 40% had "poor to very poor" fitness. Males achieved significantly higher maximal oxygen uptake than females, even when there were no differences in the severity of disease. Similar to the differences in the general population, these differences showed that male patients had higher aerobic fitness and exercise capacities than female CF patients. A significant correlation was found between self-reported exercise time and exercise intensity in the questionnaire and maximal oxygen uptake in the cardio-pulmonary test (r = 0.5, P < 0.01). The physical activity questionnaire had 85% sensitivity for the identification of patients with low aerobic exercise capacity and specificity of only 50%. CONCLUSION: The physical activity questionnaire showed a good correlation with the exercise tests results. This questionnaire should be used as a health promotion tool to adapt exercise programs for each patient.

[EATING ATTITUDES AND PRE-COMPETITION RAPID WEIGHT LOSS IN YOUNG TAEKWONDO FIGHTERS].

BACKGROUND: Taekwondo is a martial art and a combat Olympic sport. Similar to other types of combat sports, Taekwondo fights are conducted between opponents grouped by sex, age and weight classes. Disordered eating behaviors are common in combat sports with weight classes, attributed to the athletes' need to remain within a specific weight range. Pre-competition rapid weight loss (RWL) is also common, and entails a health risk. AIM: To assess the eating attitudes and the prevalence and techniques of RWL among young Taekwondo fighters. METHODS: A total of 112 competitive Taekwondo fighters in national championships and regional competitions aged 12-21.5 years completed questionnaires pertaining to eating attitudes (EAT-26) and RWL techniques. RESULTS: A total of 38% of the respondents reported precompetition RWL, with no significant between-sex difference. Common practices were training harder and eating less, but several potentially dangerous techniques were also described. Findings showed that: 70% of those reporting RWL were not assisted by another person, and the degree of RWL reached -5.5kg; 23%-40% of participants reporting RWL felt an improvement in some physical measure, yet 16% reported a decrease in subjective sport performance; 2.7% had abnormal scores on the EAT-26 questionnaire. CONCLUSIONS: There is a high rate of pre-competition RWL in young Taekwondo fighters, even in lower levels of competition. Most athletes performing RWL were unassisted, and some utilized potentially dangerous techniques. Most athletes did not feel that RWL affected their sport performance, yet a significant proportion felt decreased levels of performance. Weight-class athletes should be consulted by personnel trained in sports nutrition, in both training and competition states.

Changes in fitness are associated with changes in body composition and bone health in children after cancer.

AIM: This study examined the effects of physical activity on the fitness, body composition and mental health of children after cancer or bone marrow transplantation. METHODS: We focused on 22 children aged from seven to 14 years who had received chemotherapy and/or bone marrow transplantation in our medical centre. Ten children took part in a six-month exercise programme, and 12 children who did not exercise formed the control group. At baseline and at the end of the trial, we measured aerobic fitness, body composition, bone density and assessed the child's mood and quality of life. We pooled all participants together post hoc to compare changes in fitness with the various study outcomes. RESULTS: We found no differences between groups in changes in fitness, body composition or mental health indices. Significant correlations were found between changes in aerobic fitness and changes in lean body mass (r = 0.74, p = 0.002), bone mineral content (r = 0.57, p = 0.026) and femoral neck bone mineral density (r = 0.59, p = 0.027) in all participants. CONCLUSION: Group-based exercise training did not improve aerobic fitness in children after cancer or bone marrow transplantation. However, changes in fitness throughout the study period were associated with changes in body composition and bone health in all participants.

Vitamin D supplementation and upper respiratory tract infections in adolescent swimmers: a randomized controlled trial.

Observational studies identified associations between vitamin D insufficiency (serum 25(OH)D < 30ng·ml-1) and risk of upper respiratory infection (URI). Swimmers are highly prone to URIs, which might hinder their performance. The aim of this study was to examine if vitamin D3 supplementation reduces URI burden in vitamin D-insufficient swimmers. Fifty-five competitive adolescent swimmers with vitamin D insufficiency were randomized to receive vitamin D3 (2,000IU·d-1) or placebo for 12 winter weeks. A URI symptom questionnaire was completed weekly. Serum 25(OH)D concentrations were measured by radio-immunoassay before and after supplementation. We used linear regression to examine the relation between the change in 25(OH)D concentrations during the trial, and the duration and severity of URIs. There were no between-group differences in the frequency, severity, or duration of URIs. Exploratory analyses revealed that in the placebo group only, the change in 25(OH)D concentrations during the trial was highly associated with the duration of URIs (r = -0.90,p < .001), and moderately associated with the severity of URIs (r = -0.65,p = .043). The between-group differences for duration were highly significant. Vitamin D3 supplementation in adolescent swimmers with vitamin D insufficiency did not reduce URI burden. However, larger decreases in serum 25(OH)D concentrations were associated with significantly longer and more severe URI episodes.

Vitamin D Supplementation and Physical Performance in Adolescent Swimmers.

It is hypothesized that vitamin D insufficiency in athletes might negatively affect sport performance. The objective of this study was to examine the effect of vitamin D3 supplementation on physical performance of adolescent swimmers with vitamin D insufficiency. Fifty-three adolescent competitive swimmers with vitamin D insufficiency (serum 25-hydroxyvitamin-D concentrations (25(OH)D) < 30 ng/ml, mean 24.2 ± 4.8 ng/ml) were randomized to receive 2,000 IU/day of vitamin D3 or placebo for 12 weeks. Swimming performance at several speeds, arm-grip strength, and one-legged balance, were measured before and after supplementation. The age-adjusted changes in performance variables during the study were compared between groups. 25(OH) D concentrations at study end were significantly higher in the vitamin group compared with the placebo group (29.6 ± 6.5 ng/ml vs. 20.3 ± 4.2 ng/ml, p < .001), yet only 48% of the vitamin group became vitamin D sufficient with this dosing. No between-group differences were found in the changes of the performance variables tested. No significant differences in performance were found between participants that became vitamin D sufficient, and those who did not. No significant correlation was found between the change in serum 25(OH)D and age-adjusted balance, strength or swimming performance at study end. Vitamin D3 supplementation that raised serum 25(OH)D concentrations by a mean of 9.3 ng/ml above placebo in adolescent swimmers with vitamin D insufficiency, did not improve physical performance more than placebo.

Thymus Activity, Vitamin D, and Respiratory Infections in Adolescent Swimmers.

BACKGROUND: Several studies have identified associations between low vitamin D concentrations and risk of upper respiratory infections (URI). T lymphocytes have a major anti-viral role, are affected by vitamin D metabolism, and may mediate the link between vitamin D and URIs. Competitive swimmers have a relatively high rate of URIs, alongside a high prevalence of low vitamin D concentration. OBJECTIVES: To examine the associations linking T cell receptor excision circles (TREC, markers of thymus activity), circulating 25(OH)D concentrations and the effect of vitamin D supplementation, and URI symptoms in young competitive swimmers. METHODS: We tested 82 adolescent swimmers for serum 25(OH)D and TREC concentrations and found that 55 had vitamin D insufficiency. Randomized supplementation of either vitamin D3 or placebo was given for 12 winter weeks. URI symptoms were recorded weekly. The associations between TREC copy numbers, vitamin D and URI burden were examined. RESULTS: TREC concentrations decreased with the participants' age (r = -0.346, P = 0.003), with no significant between-gender difference. TREC concentrations did not materially differ among subjects with normal, insufficient or deficient vitamin D status, and were not affected by vitamin D supplementation. No significant correlations were found between TREC levels or their changes during the study period, and mean URI severity or duration. CONCLUSIONS: Thymus activity, represented by higher TREC levels, was not related to vitamin D concentrations or status, and was not affected by vitamin D supplementation in adolescent swimmers. TREC concentrations were not associated with URI severity or duration in this population.