Acute Effects of Vitamin D3 Supplementation on Muscle Strength in Judoka Athletes: A Randomized Placebo-Controlled, Double-Blind Trial

Relative Energy Deficiency in Sport (REDs) and knee injuries: current concepts for female athletes

In athletes, a mismatch between caloric intake and energy expended in exercise can eventually lead to Relative Energy Deficiency in Sport (REDs), where the athlete suffers from physiological derangements and decreased sport performance. The prevalence of REDs is higher in females than males. Females are already at a higher risk of knee injuries, which has been attributed to a multitude of factors such as hormonal influences, differences in musculoskeletal anatomy and neuromuscular control compared to males. The literature demonstrates an even higher risk of knee injuries in female athletes with symptoms of REDs. We propose the various factors that influence this risk. A reduction in anabolic hormones can affect muscle development and tendon repair. A relationship between poor neuromuscular control and knee injury has been established, and this can be further worsened in patients with menstrual dysfunction. Chronic deficiency in nutrients such as collagen and vitamin D can result in poorer recovery from microtrauma in tendons and ligaments. All these factors may contribute to increasing the risk of knee injuries, which may include anterior cruciate ligament tears, patella tendinopathy and patellofemoral pain syndrome. This review aims to educate sports clinicians to have a high index of suspicion when treating knee injuries in females; to screen and then manage for REDs if present, for holistic patient care.

Effects of vitamin D3 supplementation on strength of lower and upper extremities in athletes: an updated systematic review and meta-analysis of randomized controlled trials

Background

Coaches and athletes are increasingly interested in understanding athletes' serum vitamin D levels, their impact on strength, physical performance, and athletic outcomes. Previous meta-analyses were reported with limited sample size and no significant overall effect was found. Hence, it is crucial to conduct a thorough and up-to-date systematic examination and meta-analysis to elucidate the potential advantages of supplementing with vitamin D3 in enhancing muscle strength for athletes.

Methods

We performed a thorough investigation, spanning three databases (PubMed, EBSCO, and Cochrane Library), seeking randomized controlled trials (RCTs) in all languages. These trials delved into the influence of vitamin D3 supplementation on the changes of pre- and post-intervention muscle strength in healthy athletes. Our systematic examination and meta-analysis took into account serum 25(OH)D levels exceeding 30 ng/mL as a marker of adequacy.

Results

Ten RCTs, comprising 354 athletes (185 in the vitamin D3 group and 169 in the placebo group), fulfilled the inclusion criteria. During the study, 36 athletes were lost to follow-up, leaving 318 athletes (166 in the vitamin D3 group and 152 in the placebo group) with documented complete results. In comparison with the placebo group, there is a significant increase between the changes of pre- and post-intervention serum 25(OH)D levels among athletes following a period of vitamin D3 supplementation (MD 14.76, 95% CI: 8.74 to 20.77, p < 0.0001). Overall effect of four strength measurements including handgrip, one repetition maximum Bench Press (1-RM BP), vertical jump, and quadriceps contraction was not significantly improved (SMD 0.18, 95% CI: -0.02 to 0.37, p = 0.08), but there was a significant increase in quadriceps contraction (SMD 0.57, 95% CI: 0.04 to 1.11, p = 0.04).

Conclusion

This updated meta-analysis indicates the potential benefits of vitamin D supplementation for enhancing muscle strength in athletes when analyzing its quantitatively synthesized effects. With limited available studies for the quantitative synthesis, it cannot warrant significant overall enhancements in muscle strength when athletes attain adequate serum 25(OH)D levels through supplementation.

Combined Exercise Training and Nutritional Interventions or Pharmacological Treatments to Improve Exercise Capacity and Body Composition in Chronic Obstructive Pulmonary Disease: A Narrative Review

Chronic obstructive pulmonary disease (COPD) is a chronic respiratory disease that is associated with significant morbidity, mortality, and healthcare costs. The burden of respiratory symptoms and airflow limitation can translate to reduced physical activity, in turn contributing to poor exercise capacity, muscle dysfunction, and body composition abnormalities. These extrapulmonary features of the disease are targeted during pulmonary rehabilitation, which provides patients with tailored therapies to improve the physical and emotional status. Patients with COPD can be divided into metabolic phenotypes, including cachectic, sarcopenic, normal weight, obese, and sarcopenic with hidden obesity. To date, there have been many studies performed investigating the individual effects of exercise training programs as well as nutritional and pharmacological treatments to improve exercise capacity and body composition in patients with COPD. However, little research is available investigating the combined effect of exercise training with nutritional or pharmacological treatments on these outcomes. Therefore, this review focuses on exploring the potential additional beneficial effects of combinations of exercise training and nutritional or pharmacological treatments to target exercise capacity and body composition in patients with COPD with different metabolic phenotypes.

Effects of vitamin D supplementation on maximal strength and power in athletes: a systematic review and meta-analysis of randomized controlled trials

Background

Vitamin D is thought to be a powerful modulator of skeletal muscle physiology. However, available data on the effects of vitamin D supplementation on muscle function in athletes are limited and with mixed results. This meta-analysis therefore, aimed to quantitatively summarize the up-to-date literature assessing the effects of vitamin D supplementation on muscle strength and power in athletes.

Methods

Sport Discus, PubMed, Cochrane Library and Web of Science were searched to identify randomized controlled trials (RCTs) that used one-repetition maximum (1RM) tests to assess maximal strength, and vertical jump to assess muscle power in athletes. The Cochrane Risk of Bias tool was used to evaluate the included RCTs for sources of bias. The standardized mean difference (SMD) was used as the effect size, interpreted together with its 95% confidence intervals (CI). The effect sizes were calculated on the changes from baseline between vitamin D and placebo groups for maximal strength results by upper body and lower body, and for power results.

Results

Eleven RCTs involving 436 athletes were included. The results indicated that if baseline serum 25(OH)D concentration was < 75 nmol/L, the treatment had a small effect on upper body muscle strength [SMD 0.25, 95% CI: (-0.44, 0.95), p = 0.47] and on lower body muscle strength [SMD 0.26, 95% CI: (-0.13, 0.65), p = 0.19]; if the baseline serum 25(OH)D concentration was ≥ 75 nmol/L, the treatment had a trivial effect on muscle power [SMD 0.15, 95% CI: (-0.42, 0.72), p = 0.61].

Discussion

This meta-analysis demonstrated that there is not a statistically significant effect of vitamin D supplementation on improving maximum strength and power, but highlights that further research is required addressing the key limitations in previous studies before definitive conclusions can be made.

Meta-Analysis of European Clinical Trials Characterizing the Healthy-Adult Serum 25-hydroxyvitamin D Response to Vitamin D Supplementation

To obtain reliable data that allow health authorities to re-evaluate recommendations for oral vitamin D uptake, we conducted a meta-analysis to investigate the impact of supplementation on serum 25-hydroxyvitamin D (25(OH)D) levels in healthy adults in Europe. Of the publications identified (n = 4005) in our literature search (PUBMED, through 2 January 2022), 49 primary studies (7320 subjects, 73 study arms) were eligible for inclusion in our meta-analysis. The risk of bias was assessed using the Cochrane RoB tool based on seven categories, according to which each study is rated using three grades, and overall was rated as rather low. The median duration of intervention was 136.78 days (range, 1088 days); the mean weighted baseline 25(OH)D concentration and mean age were 33.01 vs. 33.84 nmol/L and 46.8 vs. 44.8 years in the vitamin D and placebo groups, respectively. Using random-effects models, 25(OH)D levels were increased by 36.28 nmol/L (95% CI 31.97-40.59) in the vitamin D group compared to the placebo, with a relative serum increment of 1.77 nmol/L per 2.5 μg of vitamin D daily. Notably, the relative serum 25(OH)D increment was affected by various factors, including the dosage and baseline serum 25(OH)D concentration, decreasing with increasing vitamin D doses and with increasing baseline serum levels. We estimate that supplementation in all healthy adults in Europe with appr. 25 μg of vitamin D (1000 IU) daily would raise serum 25(OH)D levels in 95% of the population to ≥50 nmol/L. Our work provides health authorities with reliable data that can help to re-evaluate recommendations for oral vitamin D supplementation.

Exploring the Relationship between Micronutrients and Athletic Performance: A Comprehensive Scientific Systematic Review of the Literature in Sports Medicine

The aim of this systematic review is twofold: (i) to examine the effects of micronutrient intake on athletic performance and (ii) to determine the specific micronutrients, such as vitamins, minerals, and antioxidants, that offer the most significant enhancements in terms of athletic performance, with the goal of providing guidance to athletes and coaches in optimizing their nutritional strategies. The study conducted a systematic search of electronic databases (i.e., PubMed, Web of Science, Scopus) using keywords pertaining to micronutrients, athletic performance, and exercise. The search involved particular criteria of studies published in English between 1950 and 2023. The findings suggest that vitamins and minerals are crucial for an athlete's health and physical performance, and no single micronutrient is more important than others. Micronutrients are necessary for optimal metabolic body's functions such as energy production, muscle growth, and recovery, which are all important for sport performance. Meeting the daily intake requirement of micronutrients is essential for athletes, and while a balanced diet that includes healthy lean protein sources, whole grains, fruits, and vegetables is generally sufficient, athletes who are unable to meet their micronutrient needs due to malabsorption or specific deficiencies may benefit from taking multivitamin supplements. However, athletes should only take micronutrient supplements with the consultation of a specialized physician or nutritionist and avoid taking them without confirming a deficiency.

Difference in Levels of Vitamin D between Indoor and Outdoor Athletes: A Systematic Review and Meta-Analysis

Vitamin D, its importance in different processes taking place in the human body, the effects of abnormal levels of this hormone, either too low or too high, and the need for supplementation have been extensively researched thus far. Variances in exposure to sunlight can cause vitamin D levels to fluctuate. Indoor activity can be a factor for these fluctuations and can lead to a decrease in vitamin D levels. We conducted a systematic review and meta-analysis aiming to identify whether indoor compared to outdoor training has a significant influence on vitamin D levels; we also performed subgroup analyses and multivariate meta-regression. The type of training has an impact on vitamin D levels that is influenced by multiple cofounders. In a subgroup analysis not considering cofounders, the mean serum vitamin D was 3.73 ng/mL higher in outdoor athletes, a difference which barely fails to achieve significance (p = 0.052, a total sample size of 5150). The indoor-outdoor difference is only significant (clinically and statistically) when considering studies performed exclusively on Asian athletes (a mean difference of 9.85 ng/mL, p < 0.01, and a total sample size of 303). When performing the analyses within each season, no significant differences are observed between indoor and outdoor athletes. To control for multiple cofounders (the season, latitude, and Asian/Caucasian race) simultaneously, we constructed a multivariate meta-regression model, which estimated a serum vitamin D concentration lower by 4.446 ng/mL in indoor athletes. While a multivariate model suggests that outdoor training is associated with slightly higher vitamin D concentrations when controlling for the season, latitude, and Asian/Caucasian race, the type of training has a numerically and clinically small impact. This suggests that vitamin D levels and the need for supplementation should not be decided based on training type alone.

Nutritional Strategies in the Rehabilitation of Musculoskeletal Injuries in Athletes: A Systematic Integrative Review

It is estimated that three to five million sports injuries occur worldwide each year. The highest incidence is reported during competition periods with mainly affectation of the musculoskeletal tissue. For appropriate nutritional management and correct use of nutritional supplements, it is important to individualize based on clinical effects and know the adaptive response during the rehabilitation phase after a sports injury in athletes. Therefore, the aim of this PRISMA in Exercise, Rehabilitation, Sport Medicine and Sports Science PERSiST-based systematic integrative review was to perform an update on nutritional strategies during the rehabilitation phase of musculoskeletal injuries in elite athletes. After searching the following databases: PubMed/Medline, Scopus, PEDro, and Google Scholar, a total of 18 studies met the inclusion criteria (Price Index: 66.6%). The risk of bias assessment for randomized controlled trials was performed using the RoB 2.0 tool while review articles were evaluated using the AMSTAR 2.0 items. Based on the main findings of the selected studies, nutritional strategies that benefit the rehabilitation process in injured athletes include balanced energy intake, and a high-protein and carbohydrate-rich diet. Supportive supervision should be provided to avoid low energy availability. The potential of supplementation with collagen, creatine monohydrate, omega-3 (fish oils), and vitamin D requires further research although the effects are quite promising. It is worth noting the lack of clinical research in injured athletes and the higher number of reviews in the last 10 years. After analyzing the current quantitative and non-quantitative evidence, we encourage researchers to conduct further clinical research studies evaluating doses of the discussed nutrients during the rehabilitation process to confirm findings, but also follow international guidelines at the time to review scientific literature.

Vitamin D Fortification and Its Effect on Athletes' Physical Improvement: A Mini Review

Poor vitamin D status is a widespread problem regardless of age and sex, emphasizing the necessity of new food sources to improve vitamin D levels. Currently, approximately 60% of dietary vitamin D consumption occurs via fortified foods. Vitamin D insufficiency (50-90%) is widespread according to age and region, despite different levels of sunlight exposure. The food industry must identify more effective strategies to increase normal dietary vitamin D intake and improve overall health. Strategies for vitamin D fortification include bioaddition, wherein a vitamin D-rich food source is added to staple foods during processes. These bioadditive strategies expand the range of vitamin D-containing foods and appeal to different preferences, cultures, and economic statuses. In several countries, vitamin D deficiency places athletes at a high risk of disease susceptibility. Due to low sun exposure, athletes in countries with higher and lower levels of sunlight have similar risks of vitamin D deficiency. In this review, we summarize recent technical advances to promote vitamin D utilization by humans during sports activities and in relation to the normal practices of athletes.

Neuroprotective and therapeutic effects of calcitriol in rotenone-induced Parkinson’s disease rat model

Parkinson’s disease (PD) is the second most common neurodegenerative disease. Treatment of PD is challenging, as current treatment strategies are only symptomatic and do not stop disease development. Recent studies reported neuroprotective effects of calcitriol in PD through its antioxidant and anti-inflammatory properties. The exact pathomechanisms of PD are not yet fully understood. So, investigation of different molecular pathways is challenging. Sirtuin-1 (Sirt1) modulates multiple physiological processes, including programmed cell death, DNA repair, and inflammation. Furthermore, defective autophagy is considered a key pathomechanism in PD as it eliminates protein aggregation and dysfunctional cell organelles. The present study investigated the involvement of autophagy and Sirt1/NF-κB molecular pathway in rotenone-induced PD and explored the protective and restorative effects of calcitriol through these mechanisms. Therefore, behavioral tests were used to test the effect of calcitriol on motor disability and equilibrium. Furthermore, the histological and neuronal architecture was assessed. The expression of genes encoding neuroinflammation and autophagy markers was determined by qPCR while their protein levels were determined by Western blot analysis and immune-histochemical staining. Our results indicate that behavioral impairments and dopaminergic neuron depletion in the rotenone-induced PD model were improved by calcitriol administration. Furthermore, calcitriol attenuated rotenone-induced neuroinflammation and autophagy dysfunction in PD rats through up-regulation of Sirt1 and LC3 and down-regulation of P62 and NF-κB expression levels. Thus, calcitriol could induce a neuro-protective and restorative effect in the rotenone-induced PD model by modulating autophagy and Sirt1/NF-κB pathway.

Influences of Vitamin D and Iron Status on Skeletal Muscle Health: A Narrative Review

There is conflicting evidence of the roles vitamin D and iron have in isolation and combined in relation to muscle health. The purpose of this narrative review was to examine the current literature on the roles that vitamin D and iron have on skeletal muscle mass, strength, and function and how these nutrients are associated with skeletal muscle health in specific populations. Secondary purposes include exploring if low vitamin D and iron status are interrelated with skeletal muscle health and chronic inflammation and reviewing the influence of animal-source foods rich in these nutrients on health and performance. PubMed, Scopus, SPORT Discus, EMBAE, MEDLINE, and Google Scholar databases were searched to determine eligible studies. There was a positive effect of vitamin D on muscle mass, particularly in older adults. There was a positive effect of iron on aerobic and anaerobic performance. Studies reported mixed results for both vitamin D and iron on muscle strength and function. While vitamin D and iron deficiency commonly occur in combination, few studies examined effects on skeletal muscle health and inflammation. Isolated nutrients such as iron and vitamin D may have positive outcomes; however, nutrients within food sources may be most effective in improving skeletal muscle health.

Bovine Colostrum Supplementation Improves Bone Metabolism in an Osteoporosis-Induced Animal Model

Osteoporosis is characterized by bone loss. The present study aims to investigate the effects of bovine colostrum (BC) on bone metabolism using ovariectomized (OVX) and orchidectomized (ORX) rat models. Twenty-seven-week-old Wistar Han rats were randomly assigned as: (1) placebo control, (2) BC supplementation dose 1 (BC1: 0.5 g/day/OVX, 1 g/day/ORX), (3) BC supplementation dose 2 (BC2: 1 g/day/OVX, 1.5 g/day/ORX) and (4) BC supplementation dose 3 (BC3: 1.5 g/day/OVX, 2 g/day/ORX). Bone microarchitecture, strength, gene expression of VEGFA, FGF2, RANKL, RANK and OPG, and bone resorption/formation markers were assessed after four months of BC supplementation. Compared to the placebo, OVX rats in the BC1 group exhibited significantly higher cortical bone mineral content and trabecular bone mineral content (p < 0.01), while OVX rats in the BC3 group showed significantly higher trabecular bone mineral content (p < 0.05). ORX rats receiving BC dose 2 demonstrated significantly higher levels of trabecular bone mineral content (p < 0.05). Serum osteocalcin in the ORX was pointedly higher in all BC supplementation groups than the placebo (BC1: p < 0.05; BC2, BC3: p < 0.001). Higher doses of BC induced significantly higher relative mRNA expression of OPG, VEGFA, FGF2 and RANKL (p < 0.05). BC supplementation improves bone metabolism of OVX and ORX rats, which might be associated with the activation of the VEGFA, FGF2 and RANKL/RANK/OPG pathways.

Seasonal Changes in 25(OH)D Concentration in Young Soccer Players-Implication for Bone Resorption Markers and Physical Performance

Searching for potential relations between changes in 25(OH)D concentration and in physical fitness is an interesting scientific topic. Thus, the main purpose of this study was to investigate the changes in serum concentrations of 25(OH)D in young football players in conjunction with indicators determining bone resorption and physical fitness. A total of 35 young soccer players were tested during the autumn competition period. Biochemical analysis of blood, aerobic capacity, running speed and power tests (Wingate test, squat jump, counter movement jump) were carried out at the beginning and at the end of the competition period. Significant decrements in concentration of 25(OH)D from 33.9 ± 5.87 to 23.7 ± 5.58 ng/mL were noted after the analyzed competition period. There were no significant changes in aerobic capacity along the competition period. Significant improvements were observed in 10 m sprint, 30 m sprint (p < 0.001), maximal power (p = 0.011) and total work capacity (p = 0.024). We found that the effect of changes in the players' physical fitness does not occur in relation to 25 OH(D) concentration but occurs when these changes are analyzed as a function of the duration of the observation period. Changes in physical fitness of soccer players are determined by other factors then 25(OH)D concentration.

The mechanisms of skeletal muscle atrophy in response to transient knockdown of the vitamin D receptor in vivo

KEY POINTS

Reduced vitamin D receptor (VDR) expression prompts skeletal muscle atrophy. Atrophy occurs through catabolic processes, namely the induction of autophagy, while anabolism remains unchanged. In response to VDR-knockdown mitochondrial function and related gene-set expression is impaired. In vitro VDR knockdown induces myogenic dysregulation occurring through impaired differentiation. These results highlight the autonomous role the VDR has within skeletal muscle mass regulation.

ABSTRACT

Vitamin D deficiency is estimated to affect ∼40% of the world's population and has been associated with impaired muscle maintenance. Vitamin D exerts its actions through the vitamin D receptor (VDR), the expression of which was recently confirmed in skeletal muscle, and its down-regulation is linked to reduced muscle mass and functional decline. To identify potential mechanisms underlying muscle atrophy, we studied the impact of VDR knockdown (KD) on mature skeletal muscle in vivo, and myogenic regulation in vitro in C2C12 cells. Male Wistar rats underwent in vivo electrotransfer (IVE) to knock down the VDR in hind-limb tibialis anterior (TA) muscle for 10 days. Comprehensive metabolic and physiological analysis was undertaken to define the influence loss of the VDR on muscle fibre composition, protein synthesis, anabolic and catabolic signalling, mitochondrial phenotype and gene expression. Finally, in vitro lentiviral transfection was used to induce sustained VDR-KD in C2C12 cells to analyse myogenic regulation. Muscle VDR-KD elicited atrophy through a reduction in total protein content, resulting in lower myofibre area. Activation of autophagic processes was observed, with no effect upon muscle protein synthesis or anabolic signalling. Furthermore, RNA-sequencing analysis identified systematic down-regulation of multiple mitochondrial respiration-related protein and genesets. Finally, in vitro VDR-knockdown impaired myogenesis (cell cycling, differentiation and myotube formation). Together, these data indicate a fundamental regulatory role of the VDR in the regulation of myogenesis and muscle mass, whereby it acts to maintain muscle mitochondrial function and limit autophagy.

Prevalence of Vitamin D Insufficiency and Deficiency in Young, Female Patients With Lower Extremity Musculoskeletal Complaints

BACKGROUND

Low levels of vitamin D have well-known impacts on bone health, but vitamin D also has a more global role throughout many tissues, including skeletal muscle. The high prevalence of hypovitaminosis D and the vast physiological features of vitamin D have led researchers to examine the influence of vitamin D on physical performance and injury. Because of the critical role of vitamin D in maintaining musculoskeletal health and function, a high rate of hypovitaminosis D among female patients with a variety of musculoskeletal issues could be of high clinical relevance.

HYPOTHESIS

There is a high prevalence of low vitamin D in female patients with both acute and overuse sports-related issues of both soft tissue and bone.

STUDY DESIGN

Prospective cohort study.

LEVEL OF EVIDENCE

Level 3.

METHODS

Female patients, aged 16 to 40 years, presenting with lower extremity injury diagnosed within the past 4 weeks, no use of multivitamin or vitamin D supplement, and no history of malabsorption syndrome met the inclusion criteria. Vitamin D levels were assessed and categorized as normal (≥32 ng/mL) and low, which includes insufficient (20.01-31.9 ng/mL) and deficient (≤20 ng/mL).

RESULTS

Of the 105 patients enrolled, 65.7% had low vitamin D. Within the low vitamin D cohort, 40.6% were deficient and 59.4% were insufficient. Injuries were grouped into overuse or acute with 74 overuse injuries and 31 acute injuries, exhibiting low vitamin D prevalence of 60.8% and 77.4%, respectively. Patients with ligamentous/cartilaginous injuries exhibited the highest percentage of low vitamin D (76.5%), followed by those with patellofemoral-related complaints (71.0%), muscle/tendon injuries (54.6%), and bone stress injuries (45.5%). In univariable analysis, older age, non-White race, less physical activity, less high-intensity interval training days, less endurance training days, and more rest days showed an association with low vitamin D, but none showed an independent association in multivariable analysis.

CONCLUSION

The prevalence of low vitamin D in female patients with various musculoskeletal complaints was high. Clinicians should evaluate for low vitamin D in both acute and overuse injuries.

CLINICAL RELEVANCE

In addition to screening, this study suggests that clinicians should evaluate for low vitamin D levels beyond bone stress injuries in the setting of acute and overuse injuries.

The Benefits of Vitamin D Supplementation for Athletes: Better Performance and Reduced Risk of COVID-19

The COVID-19 pandemic is having major economic and personal consequences for collegiate and professional sports. Sporting events have been canceled or postponed, and even when baseball and basketball seasons resumed in the United States recently, no fans were in attendance. As play resumed, several players developed COVID-19, disrupting some of the schedules. A hypothesis now under scientific consideration is that taking vitamin supplements to raise serum 25-hydroxyvitamin D [25(OH)D] concentrations could quickly reduce the risk and/or severity of COVID-19. Several mechanisms have been identified through which vitamin D could reduce the risks of infection and severity, death, and long-haul effects of COVID-19: (1) inducing production of cathelicidin and defensins to reduce the survival and replication of the SARS-CoV-2 virus; (2) reducing inflammation and the production of proinflammatory cytokines and risk of the "cytokine storm" that damages the epithelial layer of the lungs, heart, vascular system, and other organs; and (3) increasing production of angiotensin-converting enzyme 2, thus limiting the amount of angiotensin II available to the virus to cause damage. Clinical trials have confirmed that vitamin D supplementation reduces risk of acute respiratory tract infections, and approximately 30 observational studies have shown that incidence, severity, and death from COVID-19 are inversely correlated with serum 25(OH)D concentrations. Vitamin D supplementation is already familiar to many athletes and sports teams because it improves athletic performance and increases playing longevity. Thus, athletes should consider vitamin D supplementation to serve as an additional means by which to reduce risk of COVID-19 and its consequences.

Overexpression of the vitamin D receptor (VDR) induces skeletal muscle hypertrophy

OBJECTIVE

The Vitamin D receptor (VDR) has been positively associated with skeletal muscle mass, function and regeneration. Mechanistic studies have focused on the loss of the receptor, with in vivo whole-body knockout models demonstrating reduced myofibre size and function and impaired muscle development. To understand the mechanistic role upregulation of the VDR elicits in muscle mass/health, we studied the impact of VDR over-expression (OE) in vivo before exploring the importance of VDR expression upon muscle hypertrophy in humans.

METHODS

Wistar rats underwent in vivo electrotransfer (IVE) to overexpress the VDR in the Tibialis anterior (TA) muscle for 10 days, before comprehensive physiological and metabolic profiling to characterise the influence of VDR-OE on muscle protein synthesis (MPS), anabolic signalling and satellite cell activity. Stable isotope tracer (D2O) techniques were used to assess sub-fraction protein synthesis, alongside RNA-Seq analysis. Finally, human participants underwent 20 wks of resistance exercise training, with body composition and transcriptomic analysis.

RESULTS

Muscle VDR-OE yielded total protein and RNA accretion, manifesting in increased myofibre area, i.e., hypertrophy. The observed increases in MPS were associated with enhanced anabolic signalling, reflecting translational efficiency (e.g., mammalian target of rapamycin (mTOR-signalling), with no effects upon protein breakdown markers being observed. Additionally, RNA-Seq illustrated marked extracellular matrix (ECM) remodelling, while satellite cell content, markers of proliferation and associated cell-cycled related gene-sets were upregulated. Finally, induction of VDR mRNA correlated with muscle hypertrophy in humans following long-term resistance exercise type training.

CONCLUSION

VDR-OE stimulates muscle hypertrophy ostensibly via heightened protein synthesis, translational efficiency, ribosomal expansion and upregulation of ECM remodelling-related gene-sets. Furthermore, VDR expression is a robust marker of the hypertrophic response to resistance exercise in humans. The VDR is a viable target of muscle maintenance through testable Vitamin D molecules, as active molecules and analogues.

Association of Vitamin D Status with Lower Limb Muscle Strength in Professional Basketball Players: A Cross-Sectional Study

Vitamin D deficiency in athletes may play a role in influencing fracture risk and athletic performance. This study aimed to examine the vitamin D status of basketball players and determine its correlation with muscle strength. We included 36 male professional basketball players (mean age, 22.6 ± 3.2 years) categorized by vitamin D status. We examined the muscle strength of knee extension/flexion and ankle dorsiflexion/plantarflexion using an isokinetic dynamometer. Eleven (30.5%), fifteen (41.7%), and ten (27.8%) players had deficient (<20 ng/mL), insufficient (20–32 ng/mL), and sufficient vitamin D levels (>32 ng/mL), respectively. In the dominant side, there were no significant correlations of vitamin D level with knee extension/flexion strength (r = 0.134, p = 0.436; r = −0.017, p = 0.922, respectively), or with plantarflexion/dorsiflexion ankle strength (r = −0.143, p = 0.404; r = 1.109, p = 0.527, respectively). Moreover, the isokinetic lower limb strengths were not significantly different between the three groups in all settings (all p > 0.05). In conclusion, professional basketball players had a high prevalence of vitamin D insufficiency. Though it may not be associated with muscle strength, maintaining adequate vitamin D levels by micronutrients monitoring, regular dietician consultation, and supplementation is still a critically considerable strategy to enhance young athletes’ health.

Vitamin D and Cortisol as Moderators of the Relationship Between Testosterone and Exercise Performance in Adolescent Male Athletes

PURPOSE

Reported associations between vitamin 25(OH)D and exercise performance are equivocal, perhaps due to complex interplay with cortisol and testosterone. In this study, the authors investigated serum 25(OH)D and cortisol as moderators of the testosterone relationship with exercise performance in adolescent male athletes.

METHODS

A total of 88 ice hockey players were assessed for serum 25(OH)D, cortisol, testosterone, body composition, and exercise performance, based on countermovement jump power and muscle torque. The authors tested independent relationships, before examining complex interactions via moderated regression analyses.

RESULTS

Most athletes (62.5%) exhibited a suboptimal (20-30 ng·mL-1) serum 25(OH)D concentration, whereas 9.1% of athletes were deficient (<20 ng·mL-1). Serum 25(OH)D was not related to performance when controlling for testing year, age, and fat mass. Further modeling revealed a significant hormonal interaction. Specifically, in low-25(OH)D subjects, testosterone predicted countermovement jump power at a high (β = 7.10, effect size = .43, P < .01), but not low (β = -3.32, effect size = -.20, P = .09), cortisol concentration.

CONCLUSIONS

Serum 25(OH)D was a poor predictor of exercise performance, but it did moderate (with cortisol) the testosterone link to muscle power. Notably, this relationship emerged among individuals with a 25(OH)D concentration (∼22 ng·mL-1) approaching the deficiency cutoff. Viewing 25(OH)D as a moderating, rather than dose responsive, variable could help explain equivocal cross-sectional associations.

The Effect of Vitamin D3 Supplementation on Hepcidin, Iron, and IL-6 Responses after a 100 km Ultra-Marathon

Deficiencies in iron and vitamin D are frequently observed in athletes. Therefore, we examined whether different baseline vitamin D₃ levels have any impact on post-exercise serum hepcidin, IL-6 and iron responses in ultra-marathon runners. In this randomized control trial, the subjects (20 male, amateur runners, mean age 40.75 ± 7.15 years) were divided into two groups: experimental (VD) and control (CON). The VD group received vitamin D₃ (10,000 UI/day) and the CON group received a placebo for two weeks before the run. Venous blood samples were collected on three occasions-before the run, after the 100 km ultra-marathon and 12 h after the run-to measure iron metabolism indicators, hepcidin, and IL-6 concentration. After two weeks of supplementation, the intervention group demonstrated a higher level of serum 25(OH)D than the CON group (27.82 ± 5.8 ng/mL vs. 20.41 ± 4.67 ng/mL; p < 0.05). There were no differences between the groups before and after the run in the circulating hepcidin and IL-6 levels. The decrease in iron concentration immediately after the 100-km ultra-marathon was smaller in the VD group than CON (p < 0.05). These data show that various vitamin D₃ status can affect the post-exercise metabolism of serum iron.

Effects of Seasonal Vitamin D3 Supplementation on Strength, Power, and Body Composition in College Swimmers

The purpose of this study was to evaluate the impact of fall season vitamin D3 supplementation on strength/power, body composition, and anabolic hormones in swimmers with optimal vitamin D status at summer's end. Male and female National Collegiate Athletic Association Division I swimmers (N = 19) with optimal 25-hydroxyvitamin D [25(OH)D] randomly received 5,000 IU of vitamin D3 (VITD) or placebo (PLA) daily for 12 weeks while participating in swimming and strength and conditioning training (August-November). Before and after the intervention, the participants underwent blood sampling for analysis of serum 25(OH)D, parathyroid hormone, total testosterone, free testosterone, sex hormone-binding globulin, and insulin-like growth factor 1, dual-energy X-ray absorptiometry, and strength/power testing (bench press, squat, dead lift, standing broad jump, vertical jump, and dips and pull-ups). Sex was used as a covariate for analyses. The 25(OH)D was decreased by 44% in PLA (p < .05) and increased by 8% in VITD over the 12 weeks. Fat-free mass increased in VITD (56.4-59.1 kg; p < .05), but not PLA (59.4-59.7 kg; p < .01). Significant Group × Time interaction effects were observed for dead lift (F = 21.577, p < .01) and vertical jump (F = 11.219, p < .01), but no other strength/power tests. Total testosterone decreased similarly in both groups, but free testosterone decreased and sex hormone-binding globulin increased only in PLA (p < .01). There were no group differences or changes in insulin-like growth factor 1 with the intervention. The findings suggest that vitamin D supplementation is an efficacious strategy to maintain 25(OH)D during the fall season training and to enhance some aspects of strength/power and fat-free mass in swimmers. Further research on the relationship between vitamin D and anabolic hormones is needed.

Supplemental vitamin D3 does not affect musculoskeletal or psychomotor performance in college aged males

The experiment examined the effects 4 weeks of vitamin D (Vit D) supplementation versus placebo on musculoskeletal and psychomotor performance. Thirty-two college age males (Age: 22 ± 4 y, Height: 177.7 ± 8.3 cm, Weight: 81.5 ± 14.6 kg, BF%: 19.6 ± 7.9, Vit D: 20.0 ± 7.2 ng/ml). Participants were assigned to group (Vit D vs placebo) and remained blind throughout the study. The treatments were 4000 IU of Vit D3 or placebo (dextrose) administered daily for 4 weeks. The participants underwent baseline testing for isometric strength, explosive ability and psychomotor performance, which was repeated at week 2 and week 4. Isometric tests consisted of an Isometric Mid Thigh Pull on a Force Plate (IMTP) and an upper body isometric test (UBIST) using a load cell. Peak force during a countermovement jump (CMJ) was also determined via force plate. A psychomotor vigilance test (PVT) was used to measure sustained reaction time. Analysis of the UBIST data did not reveal a significant group × time interaction (p = 0.14; Vit D pre: 553.7 ± 168.3 N, post: 585.5 ± 150.2 N; Placebo pre: 677.7 ± 182.3 N, post: 649.8 ± 236.9 N). For IMTP no significant group × time interaction (p = 0.83; Vit D pre: 2596.4 ± 342.3 N, post: 2606.9 ± 378.3 N; Placebo pre: 2684.0 ± 432.9 N, post: 2762.6 ± 440.4 N) was found. CMJ analysis did not reveal interaction effects for group × time (p = 0.21; Vit D pre: 4429.7 ± 1619.0 N, post: 4938.5 ± 2374.8 N; Placebo pre: 5537.3 ± 3027.0 N, post: 6266.9 ± 4577.3 N). For PVT (mean reaction time) there was no significant interaction effects for group × time (p = 0.35; Vit D pre: 0.304 ± 0.041 sec, post: 0.301 ± 0.053 sec; Placebo pre: 0.295 ± 0.044 sec, post: 0.284 ± 0.029 sec). In conclusion, four weeks of Vit D supplementation was not effective in increasing musculoskeletal or psychomotor performance.

Effects of vitamin D3 supplementation on serum 25(OH)D concentration and strength in athletes: a systematic review and meta-analysis of randomized controlled trials

Background

The purpose of this systematic review and meta-analysis is to investigate the effects of vitamin D3 supplementation on skeletal muscle strength in athletes. Vitamin D3 supplements or vitamin D3 fortified foods always have claims for bringing people health benefits including bone and muscle health. An up-to-date rigorous systematic review and meta-analysis is important to better understand the effect of vitamin D3 supplementation on muscle strength.

Methods

English written randomized controlled trials (RCTs) that looked at effects of vitamin D3 supplementation on muscle strength in healthy athletes were searched using three databases (PubMed, Embase and Cochrane Library). Serum 25(OH)D above 30 ng/mL is considered to be sufficient in this systematic review and meta-analysis.

Results

Five RCTs with 163 athletes (vitamin D3 n = 86, placebo n = 77) met inclusion criteria. Fourteen athletes were lost to follow-up and 149 athletes (vitamin D3 n = 80, placebo n = 69) were documented with complete result. Among athletes with baseline serum 25(OH)D values suggesting insufficiency, vitamin D3 daily dosage at 5000 IU for over 4 weeks led to a serum 25(OH)D concentration of 31.7 ng/mL. Athletes with sufficient serum 25(OH)D level at baseline were recruited in only one study, and the participants of which were assigned to either vitamin D3 at a daily dosage of 3570 IU or placebo for 12 weeks, their serum 25(OH)D sufficiency (VD: 37.2 ± 7.6 vs. 45.6 ± 7.6; PL: 38 ± 6.8 vs. 32 ± 8.4) was well maintained above the cut-off boundary. One repetition maximum Bench Press (1-RM BP) was not improved significantly (SMD 0.07, 95% CI: − 0.32 to 0.47, P = 0.72) and there was no significant increase in maximal quadriceps contraction (SMD -2.14, 95% CI: − 4.87 to 0.59, P = 0.12). Furthermore, there was no significant overall effect of vitamin D3 intervention on muscle strength in this meta-analysis (SMD -0.75, 95% CI: − 1.82 to 0.32, P = 0.17).

Conclusion

Although, serum 25(OH)D concentrations after supplementation reached sufficiency was observed, muscle strength did not significantly improve at this point of current meta-analysis. Additional well-designed RCTs with large number of participants examined for the effect of vitamin D3 supplementation on serum 25(OH)D concentrations, muscle strength in a variety of sports, latitudes and diverse multicultural populations are needed.

Impact of Vitamin D on Physical Efficiency and Exercise Performance-A Review

Vitamin D deficiency amongst athletes and the general population seems to be a prominent problem. The most recognized role of vitamin D is its regulation of calcium homeostasis; there is a strong relationship between vitamin D and bone health. Moreover, its concentrations are associated with muscle function and immune response in both the general and athletic populations. Vitamin D level is strongly connected with the presence of VDRs (vitamin D receptors) in most human extraskeletal cells. Expression of multiple myogenic transcription factors enhancing muscle cell proliferation and differentiation is caused by an exposure of skeletal muscles to vitamin D. The aim of this review is to summarize current understanding of the significance of vitamin D on exercise performance and physical efficiency, as well to analyze the impact of vitamin D on multiple potential mechanisms. More high-quality research studies, considering free 25(OH)D as a better marker of vitamin D status, the baseline level of 25(OH)D and multiple pathways of vitamin D acting and usage in athletes are required.

Vitamin D Status Differs by Sex, Sport-Season, and Skin Pigmentation among Elite Collegiate Basketball Players

Vitamin D plays a key role in bone health, musculoskeletal function, and sport performance. Collegiate athletes competing in indoor sports may be at greater risk of vitamin D deficiency due to limited outdoor time. Therefore, the purpose was to assess 25-hydroxyvitamin D (25(OH)D) concentrations among collegiate men and women basketball (MBB, WBB) athletes. National Collegiate Athletic Association Division I men (MBB, n = 11) and women (WBB, n = 9) were tested during the off-season (T1; July) and pre-season (T2; October). Measurements included serum 25(OH)D; skin pigmentation, bone mineral density, and daily sun exposure (self-reported). Paired t-tests determined changes in 25(OH)D by sport-season and sex. Pearson correlations examined relationships between outcome variables. MBB athletes (mean ± SD; 19.6 ± 1.3 years) showed a reduction in 25(OH)D (T1: 64.53 nmol·L⁻¹ ± 11.96) (T2: 56.11 nmol·L⁻¹ ± 7.90) (p = 0.001). WBB (20.1 ± 1.1 years) had no change in 25(OH)D (T1: 99.07 nmol·L⁻¹ ± 49.94. T2: 97.56 nmol·L⁻¹ ± 36.47, p = 0.848). A positive association between 25(OH)D and skin pigmentation was observed (r = 0.47, p = 0.038). 25(OH)D was inversely correlated with lean body mass (LBM), body mass (BM), and bone mineral density (BMD), while a positive association was seen between 25(OH)D and skin pigmentation. In summary, 25(OH)D insufficiency was prevalent amongst male collegiate basketball athletes, with 25(OH)D levels being lower in the pre-season (October) than the off-season (July). Furthermore, darker skin pigmentation significantly correlated with 25(OH)D, indicating that individuals with darker skin tones may be at a greater risk of insufficiency/deficiency. More research is needed to examine the relationships between 25(OH)D and bone health in athletes.

Vitamin D Practice Patterns in National Collegiate Athletic Association Division I Collegiate Athletics Programs

CONTEXT

Vitamin D status has been associated with performance, health, and well-being in athletic populations. The measurement of vitamin D status via 25-hydroxyvitamin D [25(OH)D] testing has increased in the general population, as has vitamin D supplement use. It is unclear if similar patterns exist in collegiate athletics programs.

OBJECTIVE

To describe the clinical care related to the prevention, evaluation, and treatment of vitamin D deficiency and insufficiency used by sports medicine providers with National Collegiate Athletic Association (NCAA) Division I programs.

DESIGN

Cross-sectional study.

SETTING

Population-based online survey.

PATIENTS OR OTHER PARTICIPANTS

All NCAA Division I head athletic trainers.

MAIN OUTCOME MEASURE(S)

Information related to 25(OH)D testing, vitamin D supplementation, vitamin D-related protocols and procedures, and characteristics of athletic programs and participants.

RESULTS

We received 249 responses (72% response rate). Use of 25(OH)D testing was described by 68% of participants, with the most common indicators being health status/history (78%) and injury status/history (74%). One-fifth of participants stated that vitamin D testing was conducted as screening (without a specific cause or indication). Target blood vitamin D concentrations were highly variable. A range of 8 to 1660 annual vitamin D blood tests was reported at a cost of <$50 (8%), $51 to $100 (51%), $101 to $150 (20%), and >$150 (10%). Forty-two percent of programs covered the cost of vitamin D supplements. More than half of the participants indicated that vitamin D blood testing and supplements were not a good use of program funds. In comparison with Football Championship Subdivision programs, Football Bowl Subdivision programs were more likely to conduct vitamin D testing and pay for vitamin D supplements, and their providers were more likely to believe that testing and supplements were a good use of program funds.

CONCLUSIONS

A great deal of variability was present in vitamin D-related clinical practices among NCAA Division I athletics programs, which reflects existing contradictions and uncertainty in research, recommendations, and guidelines. Knowledge of current practice patterns is important in evaluating and establishing best practices, policies, and procedures for sports medicine and sports nutrition professionals in the collegiate setting.

A single mega dose of vitamin D3 improves selected physical variables in vitamin D-deficient young amateur soccer players: a randomized controlled trial

This randomized controlled trial aimed to test whether vitamin D (VD) supplementation affects measures of physical performance in VD-deficient, mildly trained children. Thirty-six recreationally soccer player boys were randomly assigned to single dose (200 000 IU) of VD3 (n = 19) or placebo (n = 17). Plasma 25-hydroxyvitamin D (25-OHD) was assessed and measures of physical performance (i.e., vertical and standing broad jumps, triple hop, 10-m and 30-m sprints, shuttle run) were performed before and 12 weeks after the loading dose. Mixed ANCOVA models were performed and effect size was estimated by partial eta squared (η_p²). Baseline 25-OHD and physical variables were equivalent in the 2 groups. Twelve weeks after VD loading, plasma 25-OHD increased and physical variables improved only in the VD group. There was a significant interaction effects for group by time for vertical jump (F = 14.9, p = 0.001, η_p² = 0.394), triple hop jump (F = 24.2, p < 0.001, η_p² = 0.513), 10-m (F = 4.46, p = 0.046, η_p² = 0.162) and 30-m (F = 6.56, p = 0.017, η_p² = 0.222) sprints, and shuttle run (F = 13.4, p = 0.001, η_p² = 0.369). In conclusion, a single bolus of VD3 resulted in significant improvements in jumping ability, agility, and running speed in mildly trained children that are deficient in VD. The findings suggest that correcting VD deficit might be beneficial for physical performance. Novelty A mega dose of VD3 improves jumping ability, agility, and running speed in VD-deficient, mildly trained children. Effect of VD on measures of physical performance is noticeable 3 months after the loading dose.

Vitamin D, Skeletal Muscle Function and Athletic Performance in Athletes-A Narrative Review

The active form of vitamin D (calcitriol) exerts its biological effects by binding to nuclear vitamin D receptors (VDRs), which are found in most human extraskeletal cells, including skeletal muscles. Vitamin D deficiency may cause deficits in strength, and lead to fatty degeneration of type II muscle fibers, which has been found to negatively correlate with physical performance. Vitamin D supplementation has been shown to improve vitamin D status and can positively affect skeletal muscles. The purpose of this study is to summarize the current evidence of the relationship between vitamin D, skeletal muscle function and physical performance in athletes. Additionally, we will discuss the effect of vitamin D supplementation on athletic performance in players. Further studies are necessary to fully characterize the underlying mechanisms of calcitriol action in the human skeletal muscle tissue, and to understand how these actions impact the athletic performance in athletes.

Efficacy of Vitamin D Supplementation in Physical Performance of Iranian Elite Athletes

Background:

There has been no report of the vitamin D status of the professional athletes from Iran to date. This study was performed to evaluate the efficacy of weekly vitamin D supplementation on athletic performance in Iranian athletes expedited to Asian competition in Taipei, China, 2015.

Methods:

This study was a randomized controlled clinical trial. Seventy subjects were enrolled in the study. The athletes were randomly divided into two groups: vitamin D supplement (D; received 50,000 IU of vitamin D supplement weekly) and control (P, received a placebo weekly). Duration of the study was 8 weeks. Anthropometric, dietary, athletic performance, and biochemical evaluations were performed for all subjects in the beginning and in the end of the intervention period.

Results:

A significant rise in circulating 25(OH)D concentration was observed in D group (17.3 ± 16.9 ng/mL, P < 0.001), whereas in P group, there was a statistically significant decrement (−3.1 ± 8.4 ng/mL, P = 0.040). There were no either within- or between-group significant differences in Ergo jump, vertical jump, and agility tests. In strength leg press tests, both groups showed a significant improvement. However, comparisons of changes revealed that the improvement in D group was significantly higher than in P group (P = 0.034). Moreover, in sprint test (one repetition-Max, 1RM), only D group had a significant within-group improvement (P = 0.030).

Conclusions:

Weekly supplementation with 50,000 IU vitamin D resulted in nearly 17 ng/mL increment in circulating calcidiol. This increase was associated with significant improvement of power leg press and sprint tests in D-supplemented group.

Effect of vitamin D supplementation on upper and lower limb muscle strength and muscle power in athletes: A meta-analysis

BACKGROUND

Vitamin D may play a role in skeletal muscle because of the discovery of VDR in skeletal muscle. However, vitamin D deficiency is a global problem, including athletes. Studies examining the effect of vitamin D supplementation on muscle function in athletes have inconsistent results. Therefore, we aimed to quantitatively summarize the evidence for the effect of vitamin D supplementation on skeletal muscle strength and explosive power of athletes using a meta-analysis.

METHODS

PubMed, EMBASE, Cochrane Library, and Web of Science were searched for studies to identify randomized controlled trials or controlled trials meeting the inclusion criteria. By a meta-analysis, effect sizes (standardized mean differences, SMD) with 95% confidence intervals (CI) was calculated to compare reported outcomes across studies, I2 index was used to assessing heterogeneity, and heterogeneity factors were identified by regression analysis. The potential publication and sensitivity analyses were also assessed.

RESULTS

Eight RCTs involving 284 athletes were included. The protocols used to evaluate the muscle strength of athletes were inconsistent across the included studies, and muscle explosive power was assessed via vertical jump tests. The results indicated that vitamin D supplementation had no impact on overall muscle strength outcomes (SMD 0.05, 95% CI: -0.39 to 0.48, p = 0.84). In subgroup analysis, vitamin D supplementation had an effect on lower-limb muscle strength (SMD 0.55, 95% CI:0.12 to 0.98, p = 0.01) but not upper-limb muscle strength (SMD -0.19, 95% CI:-0.73 to 0.36, p = 0.50) or muscle explosive power (SMD 0.05, 95% CI:-0.24 to 0.34, p = 0.73). Vitamin D supplementation was more effective for athletes trained indoors (SMD 0.48, 95% CI:0.06 to 0.90, p = 0.02).

CONCLUSIONS

Vitamin D supplementation positively affected lower limb muscle strength in athletes, but not upper limb muscle strength or muscle power. Different muscle groups and functions may respond differently to vitamin D supplementation. Additional studies should focus on determining the appropriate vitamin D supplementation methods and optimal serum 25(OH)D levels for athletes.

REGISTRATION

The protocol for our study is registered in the international prospective register of systematic reviews (PROSPERO registration number CRD42016045872).

High prevalence of vitamin D insufficiency in professional handball athletes

OBJECTIVES

Vitamin D affects multiple body functions through the regulation of gene expression. In sports medicine, its influence on musculoskeletal health and performance is of particular interest. Vitamin D insufficiency might decrease athletic performance and increase the risk of musculoskeletal injuries. Several studies have demonstrated vitamin D deficiency in professional athletes; however, the prevalence of vitamin D insufficiency in professional handball players is yet unknown.

METHODS

The study was planned as a prospective, non-interventional study. We examined 70 male elite handball athletes (first league) in a pre-competition medical assessment in July. Age, height, weight, body mass index, 25-OH vitamin D, calcium, and parathyroid hormone were evaluated, and a sun exposure score was calculated. Players were then divided into two groups of vitamin D levels: insufficient (<30 ng/mL) and sufficient (≥30 ng/mL).

RESULTS

The mean 25-OH vitamin D level of the 70 players was 33.5 ± 10.9 ng/mL (median 32.2, IQR 26.5-38.9 ng/mL). Thirty-nine (55.7%) had sufficient and 31 (44.3%) insufficient levels. Athletes with sufficient vitamin D levels had significantly lower parathyroid hormone levels than athletes with insufficiency (24.9 ± 12.1 vs. 33.5 ± 15.1 ng/mL, p = 0.02). All other parameters evaluated demonstrated no significant difference between the two groups.

CONCLUSION

Vitamin D insufficiency is a common finding in professional handball athletes even in summer, which might negatively affect physical performance. Furthermore, it might lead to an increased risk of musculoskeletal injuries and infections. This should be evaluated in further studies.

The Effect of Abnormal Vitamin D Levels in Athletes

Vitamin D is a lipophilic prohormone integral to musculoskeletal, autoimmune, oncologic, cardiovascular, and mental health. Of particular importance to the orthopedic surgeon is the role of vitamin D in the regulation of bone mass, muscle strength, and physical performance. Although vitamin D-related skeletal pathologies are rare in industrialized nations, emerging research in the field has shown that most American adults have inadequate levels of vitamin D. Even among athletes, there is a high prevalence of vitamin D deficiency, which may place competitors at risk of stress fractures, illness, and delayed muscle recovery. Adequately identifying vitamin D-deficient individuals in need of supplementation is important to help optimize performance and prevent future injury. The goal of this review is to describe the epidemiology of vitamin D deficiency and its effects on athletic performance and musculoskeletal health. Future double-blinded studies of vitamin D supplementation in athletes are needed. We recommend treating athletes who have insufficient or deficient vitamin D levels.

Effect of Vitamin D on Muscle Function and Injury in Elite Adolescent Dancers: A Randomized Double-Blind Study

PURPOSE

A number of studies have noted low levels of vitamin D in dancers, and this has been associated with increased risk of injuries and decreased muscle-strength indices. The aim of the present study was to examine whether vitamin D supplementation over a 4-mo period can improve muscle function and injury incidence.

METHODS

A total of 84 participants volunteered; exclusion criteria and dropout (19%) reduced the cohort to 67 participants (females = 29 and males = 38; 17-19 y). Participants were randomly assigned to either an intervention or placebo group (2∶1 ratio). All provided a venous blood sample before and after the 4-mo study period. The intervention group received 120,000 IU vitamin D to be taken over a 1-wk period, and the placebo group received the same number of inert pills. Participants completed a series of muscle function tests before and after the monitoring period. Injury incidence was recorded by the independent health team at the school.

RESULTS

Preintervention, 6% of the cohort were vitamin D deficient, 81% were insufficient, and 13% had sufficient levels; postintervention, 53% were insufficient and 47% were sufficient. The intervention group reported a significant increase in serum 25(OH)D3 (57%; P < .00) and isometric strength (7.8%; P = .022) but not muscle power. There was a significant association between traumatic injury occurrence for the intervention and control groups (10.9% vs 31.8%; P < .02).

CONCLUSION

Vitamin D supplementation decreased the numbers of deficient and insufficient participants in this cohort. The intervention group reported a small significant increase in muscle strength that was negatively associated with traumatic injury occurrence.

Effects of Vitamin D Supplementation on Serum 25-Hydroxyvitamin D Concentrations and Physical Performance in Athletes: A Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND

There is currently no systematic review examining the effects of vitamin D supplementation among athletes. A rigorous systematic review and meta-analysis is important to provide a balanced view of current knowledge on the effect of vitamin D on serum 25-hydroxyvitamin D [25(OH)D] concentrations and physical performance.

OBJECTIVES

This systematic review of randomized controlled trials (RCTs) evaluated the effects of oral vitamin D supplementation on serum 25(OH)D concentrations and physical performance in athletes.

METHODS

Multiple electronic databases were searched, and study eligibility, methodological quality assessment, and data extraction were completed independently and in duplicate. Studies were stratified by baseline vitamin D sufficiency, season, and latitude. A cut-off of 30 ng/ml (75 nmol/l) of 25(OH)D was used for sufficiency. Absolute mean differences (AMDs) between vitamin D and placebo using random effects analysis, and heterogeneity using Q statistic and I ² index, were calculated. AMD with 95% confidence interval (CI), p value, and I ² are reported.

RESULTS

In total, 13 RCTs (2005-2016) with 532 athletes (vitamin D 311, placebo 221) were eligible. A total of 433 athletes (vitamin D 244, placebo 189) had complete outcome data. Among athletes with baseline values suggesting insufficiency, vitamin D supplementation led to significant increases from 3000 IU (AMD 15.2 ng/ml; 95% CI 10.7-19.7, p < 0.0001, I ² = 0%) and 5000 IU (AMD 27.8 ng/ml; 95% CI 16.9-38.8, p < 0.0001, I ² = 78%) per day at >45° latitudes. Both doses led to sufficiency concentrations during winter months. Among athletes with baseline vitamin D suggesting sufficiency, serum 25(OH)D sufficiency was maintained from different doses at both latitudes. Of 13 included trials, only seven measured different physical performances and none demonstrated a significant effect of vitamin D supplementation during 12 weeks of follow-up.

CONCLUSION

Despite achieving sufficiency in vitamin D concentrations from ≥3000 IU supplementation, physical performance did not significantly improve. Between-study heterogeneity was large, and well-designed RCTs examining the effect of vitamin D supplementation on serum 25(OH)D concentrations, physical performance, and injuries in different sports, latitudes, ethnicities, and vitamin D status are needed.

Correcting Vitamin D Insufficiency Improves Some But Not All Aspects of Physical Performance During Winter Training in Taekwondo Athletes

We investigated the effects of vitamin D₃ supplementation on physical performance during winter training in vitamin D insufficient taekwondo athletes. Thirty-five collegiate male and female taekwondo athletes, aged 19-22 years with low serum 25(OH)D concentration (28.8 ± 1.10 nmol/L), were randomly assigned to a vitamin D group (n = 20) or a placebo group (n = 15). Subjects received either a vitamin D₃ capsule (5,000 IU/day) or a placebo during 4 weeks of winter training. Blood samples were collected for analyzing serum 25(OH)D concentration. Physical performance tests included Wingate anaerobic test, isokinetic muscle strength and endurance, a countermovement jump test, sit-ups, agility test, and 20-m pacer. Serum 25(OH)D concentrations increased significantly in the vitamin D group (96.0 ± 3.77 nmol/L) after 4 weeks of supplementation, but no changes were found in the placebo group (F = 242.44, p = .000). There were significant interaction effects for anaerobic peak power (F = 7.49, p = .010) and isokinetic knee extension at 180 deg/s (F = 6.08, p = .019). Changes in serum 25(OH)D concentration were positively associated with changes in peak power and isokinetic knee extension at 180 deg/s. However, no significant interaction effects were observed in other performance variables. This study suggests that 4 weeks of vitamin D supplementation elevates serum 25(OH)D concentration to sufficient levels. Correcting vitamin D insufficiency improves some but not all aspects of performance. Thus, efficacy of vitamin D supplementation to enhance performance remains unclear.

Vitamin D status and its relation to exercise performance and iron status in young ice hockey players

Objectives

The aim was to examine the association between serum vitamin D concentration and isometric strength of various muscle groups, vertical jump performance, and repeated sprint ability in young ice hockey players. The secondary aim was to determine the association between vitamin D deficiency and indices of iron status.

Methods

Fifty male ice hockey players (17.2±0.9 years) participated in this cross-sectional study. Exercise performance was evaluated using isometric strength measures of upper and lower extremities, vertical jump performance and repeated sprint ability (RSA). Blood samples were collected for the determination of serum 25-hydroxyvitamin D (25(OH)D) and multiple indicies of iron status.

Results

The mean serum 25(OH)D concentration was 30.4 ng·ml^-1 and ranged from 12.5 to 91.4 ng·ml^-1. Eleven participants (22%) had vitamin D deficiency and 20 athletes (40%) had vitamin D insufficiency. Serum 25(OH)D concentration was not positively correlated with isometric muscle strength, vertical jump performance, or RSA after adjusting for age, training experience, fat mass, fat free mass and height. Serum 25(OH)D concentration was not associated with indices of iron status.

Conclusion

Vitamin D insufficiency is highly prevalent in ice hockey players, but 25(OH)D concentration but it is not associated with exercise performance or indices of iron status.

Postnatal Vitamin D Intake Modulates Hippocampal Learning and Memory in Adult Mice

Vitamin D (VD) is a neuroactive steroid crucial for brain development, function and homeostasis. Its deficiency is associated with numerous brain conditions. As such, VD and its variants are routinely taken by a broad of groups with/without known VD deficiency. In contrast, the harmful effects of VD overdose have been poorly studied. Similarly, the developmental stage-specific VD deficiency and overdose have been rarely explored. In the present work, we showed that postnatal VD supplementation enhanced the motor function transiently in the young adult, but not in the older one. Postnatal VD intake abnormality did not impact the anxiety and depressive behavior but was detrimental to spatial learning and hippocampus-dependent memory. At the molecular level we failed to observe an obvious and constant change with the neural development and activity-related genes examined. However, disrupted developmental expression dynamics were observed for most of the genes, suggesting that the altered neural development dynamics and therefore aberrant adult plasticity might underlie the functional deficits. Our work highlights the essence of VD homeostasis in neural development and adult brain function. Further studies are needed to determine the short- and long-term effects VD intake status may have on brain development, homeostasis, and diseases.

The Association of Vitamin D Status in Lower Extremity Muscle Strains and Core Muscle Injuries at the National Football League Combine

PURPOSE

To evaluate the association between serum vitamin D level and the prevalence of lower extremity muscle strains and core muscle injuries in elite level athletes at the National Football League (NFL) combine.

METHODS

During the 2015 NFL combine, all athletes with available serum vitamin D levels were included for study. Baseline data were collected, including age, race, body mass index, position, injury history specific to lower extremity muscle strain or core muscle injury, and Functional Movement Screen scores. Serum 25-hydroxyvitamin D was collected and defined as normal (≥32 ng/mL), insufficient (20-31 ng/mL), and deficient (<20 ng/mL). Univariate regression analysis was used to examine the association of vitamin D level and injury history. Subsequent multivariate regression analysis was used to examine this relation with adjustment for collected baseline data variables.

RESULTS

The study population included 214 athletes, including 78% African American athletes and 51% skilled position players. Inadequate vitamin D was present in 59%, including 10% with deficient levels. Lower extremity muscle strain or core muscle injury was present in 50% of athletes, which was associated with lower vitamin D levels (P = .03). Athletes with a positive injury history also showed significantly lower vitamin D levels as compared with uninjured athletes (P = .03). African American/black race (P < .001) and injury history (P < .001) was associated with lower vitamin D. Vitamin D groups showed no differences in age (P = .9), body mass index (P = .9), or Functional Movement Screen testing (P = .2). Univariate analysis of inadequate vitamin D levels showed a 1.86 higher odds of lower extremity strain or core muscle injury (P = .03), and 3.61 higher odds of hamstring injury (P < .001). Multivariate analysis did not reach an independent association of low vitamin D with injury history (P = .07).

CONCLUSIONS

Inadequate vitamin D levels are a widespread finding in athletes at the NFL combine. Players with a history of lower extremity muscle strain and core muscle injury had a higher prevalence of inadequate vitamin D.

LEVEL OF EVIDENCE

Level IV, retrospective study-case series.

Relationship between 25(OH)D levels and athletic performance in elite Polish judoists

There is a growing body of evidence for a role of vitamin D in muscle function and for its influence on athletic performance, injury profile and recovery in well-trained athletes. The aim of our study was to assess the relationship between 25(OH)D levels and hand grip strength, lower limb isokinetic strength and muscle power in elite judoists. We enrolled 25 Polish elite judoists. The mean age was 21.9±9.8 years, the mean height was 179.2±6.6 cm, the mean body mass was 79.1±8.7 kg, and the mean career duration was 11.5±3.9 years. Serum levels of 25(OH)D and parathormone (PTH) were measured by electrochemiluminescence (ECLIA) using the Elecsys system (Roche, Switzerland). Serum calcium was determined by colorimetry using the Konelab 60 system from bioMérieux (France). Lower limb strength was tested with the Biodex Multi-Joint 4 Isokinetic Dynamometer (Biodex Medical System, New York, USA), and hand grip strength was measured with a manual dynamometer (TAKEI, Japan). Muscle power was determined with the electronic jump mat OptoJump (Microgate, Bolzano, Italy). Our study showed decreased serum 25(OH)D levels in 80% of the professional judoists. The results also demonstrated a statistically significant positive correlation between vitamin D levels and left hand grip strength, muscle power assessed by vertical jump, and total work in left and right knee extensors at an angular velocity of 60°/s. Based on our results it can be concluded that in well-trained professional athletes, there may be a relationship between serum levels of 25(OH)D and skeletal muscle strength, power, and work.

Vitamin D and calcium supplementation, skeletal muscle strength and serum testosterone in young healthy adult males: Randomized control trial

BACKGROUND

Cholecalciferol and/or calcium supplementation might increase skeletal muscle strength and serum testosterone in young adult males.

OBJECTIVE

We performed a randomized control trial assessing the effect of cholecalciferol/calcium on skeletal muscle strength and serum testosterone in vitamin D deficient young males.

DESIGN

Two-by-two factorial RCT.

SUBJECT AND INTERVENTION

Two-hundred and twenty-eight young males were block-randomized to (i) double-placebo, (ii) calcium/placebo, (iii) cholecalciferol/placebo and (iv) cholecalciferol/calcium. Doses for cholecalciferol were 60 000 IU/wk for 8 weeks followed by 60 000 IU/fortnightly, and doses for elemental calcium were 500 mg/twice daily for 6 months. A total of 180 subjects completed the study protocol. Their  ean age, body mass index and baseline 25(OH)D were 20.2 ± 2.2 years, 23.0 ± 3.6 kg/m² and 21.5 ± 9.5 nmol/L, respectively.

MEASUREMENTS

Handgrip (primary outcome), pinch-grip strength, distance walked in 6 minutes, dyspnoea-score, quality of life by Short Form 36, serum 25(OH)D, 1,25(OH)₂ D, iPTH, total testosterone and free androgen index (FAI).

RESULTS

After intervention, mean serum 25(OH)D was >75.0 nmol/L in cholecalciferol groups. However, the handgrip strength (29.7 ± 4.4, 29.3 ± 4.6, 30.6 ± 5.0 and 28.8 ± 4.3 kg, P = .28) was comparable in the 4 groups. Subgroups analysis among subjects with baseline serum 25OH)D < 25.0 and <12.0 nmol/L showed similar results. The mean serum testosterone decreased significantly at 6 months; however, delta change was similar in 4 groups. Change in handgrip strength and other outcomes was similar in 4 groups with and without adjustment for delta testosterone and FAI.

CONCLUSIONS

Six months of cholecalciferol/calcium supplementation had no significant effect on skeletal muscle strength and serum testosterone in young adult males.

Vitamin D3 Supplementation Does Not Improve Sprint Performance in Professional Rugby Players: A Randomized, Placebo-Controlled, Double-Blind Intervention Study

Vitamin D insufficiency is common in athletes and may lower physical performance. Many cross-sectional studies associate vitamin D status with physical performance in athletes; however, there have been few prospective randomized controlled trials with adequate statistical power to test this relationship, and none in the southern hemisphere. Thus, a prospective double-blind, randomized, placebo-controlled intervention trial was conducted involving 57 professional rugby union players in New Zealand. Participants were randomized to receive 50,000 IU of cholecalciferol (equivalent to 3,570 IU/day) or placebo once every two weeks over 11-12 weeks. Serum 25(OH)D concentrations and physical performance were measured at baseline, weeks 5-6, and weeks 11-12. Mean (SD) serum 25(OH)D concentrations for all participants at baseline was 94 (18) nmol/L, with all players above 50 nmol/L. Vitamin D supplementation significantly increased serum 25(OH)D concentrations compared to placebo, with a 32 nmol/L difference between groups at 11-12 weeks (95% CI, 26-38; p < 0.001). Performance in five of the six tests at study completion, including the primary outcome variable of 30-m sprint time, did not differ between the vitamin D supplemented and placebo groups (p > 0.05). Performance on the weighted reverse-grip chin up was significantly higher in players receiving vitamin D compared with placebo, by 5.5 kg (95% CI, 2.0-8.9; p = 0.002). Despite significantly improving vitamin D status in these professional rugby union players, vitamin D supplementation had little impact on physical performance outcomes. Thus, it is unlikely that vitamin D supplementation is an ergogenic aid in this group of athletes.

Effect of 12-Week Vitamin D Supplementation on 25[OH]D Status and Performance in Athletes with a Spinal Cord Injury

(1) BACKGROUND: studies with able-bodied athletes showed that performance might possibly be influenced by vitamin D status. Vitamin D seems to have a direct impact on neuromuscular function by docking on vitamin D receptors in the muscle tissue. Additionally, a high prevalence of vitamin D deficiency was shown not only in infants and in the elderly but also in healthy adults and spinal cord injured individuals. Therefore, the aim of our study was to investigate whether a vitamin D dose of 6000 IU daily over 12 weeks would be sufficient to increase vitamin D status in indoor wheelchair athletes to a normal or optimal vitamin D level and whether vitamin D deficiency is associated with an impairment in muscle performance in these individuals; (2) METHODS: vitamin D status was assessed in indoor elite wheelchair athletes in order to have a baseline measurement. If vitamin D status was below 75 nmol/L, athletes were supplemented with 6000 IU of vitamin D daily over 12 weeks. A vitamin D status over 75 nmol/L was supplemented with a placebo supplement. Vitamin D status, as well as a Wingate test and an isokinetic dynamometer test, were performed at baseline and after six and 12 weeks; (3) RESULTS: 20 indoor elite wheelchair athletes participated in this double-blind study. All of these athletes showed an insufficient vitamin D status at baseline and were, therefore, supplemented with vitamin D. All athletes increased vitamin D status significantly over 12 weeks and reached an optimal level. Wingate performance was not significantly increased. Isokinetic dynamometer strength was significantly increased but only in the non-dominant arm in isometric and concentric elbow flexion; (4) CONCLUSION: a dose of 6000 IU of vitamin D daily over a duration of 12 weeks seems to be sufficient to increase vitamin D status to an optimal level in indoor wheelchair athletes. It remains unclear, whether upper body performance or muscle strength and vitamin D status are associated with each other.

25(OH)D Status of Elite Athletes with Spinal Cord Injury Relative to Lifestyle Factors

Background: Due to the potential negative impact of low Vitamin D status on performance-related factors and the higher risk of low Vitamin D status in Spinal Cord Injury (SCI) population, research is warranted to determine whether elite athletes with SCI have sufficient 25(OH)D levels. The purposes of this study were to examine: (1) the seasonal proportion of vitamin D insufficiency among elite athletes with SCI; and (2) to determine whether lifestyle factors, SCI lesion level, and muscle performance/function are related to vitamin D status in athletes with SCI. Methods: Thirty-nine members of the Canadian Wheelchair Sports Association, and the US Olympic Committee Paralympic program from outdoor and indoor sports were recruited for this study. Dietary and lifestyle factors, and serum 25(OH)D concentrations were assessed during the autumn (October) and winter (February/March). An independent t-test was used to assess differences in 25(OH)D status among seasons, and indoor and outdoor sports in the autumn and winter, respectively. Results: Mean ± SD serum 25(OH)D concentration was 69.6 ± 19.7 nmol/L (range from 30 to 107.3 nmol/L) and 67.4 ± 25.5 nmol/L (range from 20 to 117.3 nmol/L)in the autumn and winter, respectively. In the autumn, 15.4% of participants were considered vitamin D deficient (25(OH)D < 50 nmol/L) whereas 51.3% had 25(OH)D concentrations that would be considered insufficient (<80 nmol/L). In the winter, 15.4% were deficient while 41% of all participants were considered vitamin D insufficient. Conclusion: A substantial proportion of elite athletes with SCI have insufficient (41%–51%) and deficient (15.4%) 25(OH)D status in the autumn and winter. Furthermore, a seasonal decline in vitamin D status was not observed in the current study.