Daniel J. Owens

Assessment of vitamin D concentration in non-supplemented professional athletes and healthy adults during the winter months in the UK: implications for skeletal muscle function

Abstract The current study implemented a two-part design to (1) assess the vitamin D concentration of a large cohort of non-vitamin D supplemented UK-based athletes and 30 age-matched healthy non-athletes and (2) to examine the effects of 5000 IU · day−1 vitamin D3 supplementation for 8-weeks on musculoskeletal performance in a placebo controlled trial. Vitamin D concentration was determined as severely deficient if serum 25(OH)D < 12.5 nmol · l−1, deficient 12.5–30 nmol · l−1 and inadequate 30–50 nmol · l−1. We demonstrate that 62% of the athletes (38/61) and 73% of the controls (22/30) exhibited serum total 25(OH)D < 50 nmol · l−1. Additionally, vitamin D supplementation increased serum total 25(OH)D from baseline (mean ± SD = 29 ± 25 to 103 ± 25 nmol · l−1, P = 0.0028), whereas the placebo showed no significant change (53 ± 29 to 74 ± 24 nmol · l−1, P = 0.12). There was a significant increase in 10 m sprint times (P = 0.008) and vertical-jump (P = 0.008) in the vitamin D group whereas the placebo showed no change (P = 0.587 and P = 0.204 respectively). The current data supports previous findings that athletes living at Northerly latitudes (UK = 53° N) exhibit inadequate vitamin D concentrations (<50 nmol · l−1). Additionally the data suggests that inadequate vitamin D concentration is detrimental to musculoskeletal performance in athletes. Future studies using larger athletic groups are now warranted.

The effects of vitamin D(3) supplementation on serum total 25[OH]D concentration and physical performance:a randomised dose-response study

Background Vitamin D deficiency is common in the general public and athletic populations and may impair skeletal muscle function. We therefore assessed the effects of vitamin D3 supplementation on serum 25[OH]D concentrations and physical performance. Methods 30 club-level athletes were block randomised (using baseline 25[OH]D concentrations) into one of three groups receiving either a placebo (PLB), 20 000 or 40 000 IU/week oral vitamin D3 for 12 weeks. Serum 25[OH]D and muscle function (1-RM bench press and leg press and vertical jump height) were measured presupplementation, 6 and 12 weeks postsupplementation. Vitamin D deficiency was defined in accordance with the US Institute of Medicine guideline (<50 nmol/l). Results 57% of the subject population were vitamin D deficient at baseline (mean±SD value 51±24 nmol/l). Following 6 and 12 weeks supplementation with 20 000 IU (79±14 and 85±10 nmol/l, respectively) or 40 000 IU vitamin D3 (98±14 and 91±24 nmol/l, respectively), serum vitamin D concentrations increased in all participants, with every individual achieving concentrations greater than 50 nmol/l. In contrast, vitamin D concentration in the PLB group decreased at 6 and 12 weeks (37±18 and 41±22 nmol/l, respectively). Increasing serum 25[OH]D had no significant effect on any physical performance parameter (p>0.05). Conclusions Both 20 000 and 40 000 IU vitamin D3 supplementation over a 6-week period elevates serum 25[OH]D concentrations above 50 nmol/l, but neither dose given for 12 weeks improved our chosen measures of physical performance.

Lifelong training preserves some redox-regulated adaptive responses after an acute exercise stimulus in aged human skeletal muscle

Several redox-regulated responses to an acute exercise bout fail in aged animal skeletal muscle, including the ability to upregulate the expression of antioxidant defense enzymes and heat shock proteins (HSPs). These findings are generally derived from studies on sedentary rodent models and thus may be related to reduced physical activity and/or intraspecies differences as opposed to aging per se. This study, therefore, aimed to determine the influence of age and training status on the expression of HSPs, antioxidant enzymes, and NO synthase isoenzymes in quiescent and exercised human skeletal muscle. Muscle biopsy samples were obtained from the vastus lateralis before and 3 days after an acute high-intensity-interval exercise bout in young trained, young untrained, old trained, and old untrained subjects. Levels of HSP72, PRX5, and eNOS were significantly higher in quiescent muscle of older compared with younger subjects, irrespective of training status. 3-NT levels were elevated in muscles of the old untrained but not the old trained state, suggesting that lifelong training may reduce age-related macromolecule damage. SOD1, CAT, and HSP27 levels were not significantly different between groups. HSP27 content was upregulated in all groups studied postexercise. HSP72 content was upregulated to a greater extent in muscle of trained compared with untrained subjects postexercise, irrespective of age. In contrast to every other group, old untrained subjects failed to upregulate CAT postexercise. Aging was associated with a failure to upregulate SOD2 and a downregulation of PRX5 in muscle postexercise, irrespective of training status. In conclusion, lifelong training is unable to fully prevent the progression toward a more stressed muscular state as evidenced by increased HSP72, PRX5, and eNOS protein levels in quiescent muscle. Moreover, lifelong training preserves some (e.g., CAT) but not all (e.g., SOD2, HSP72, PRX5) of the adaptive redox-regulated responses after an acute exercise bout. Collectively, these data support many but not all of the findings from previous animal studies and suggest parallel aging effects in humans and mice at rest and after exercise that are not modulated by training status in human skeletal muscle.

Vitamin D and the athlete: Emerging insights

Abstract Interest in Vitamin D has risen considerably recently with many athletes now advised to take daily vitamin D supplements. The reason for this interest is partly not only attributed to the resurgence of the Vitamin D-deficient disease rickets but also due to the discovery of a Vitamin D receptor in many tissues suggesting a more global role for Vitamin D than previously considered. Unlike the other vitamins that are obtained through the diet, Vitamin D is unique since endogenous synthesis following ultraviolet B (UVB) exposure is the predominant route of entry into systemic circulation. Moreover, Vitamin D could be better classed as a seco-steroid, given that its structure is similar to that of a steroid, and its production is derived from a cholesterol precursor (7-dehydrocholesteol) in the skin. The classification of Vitamin D status is currently subject to considerable debate with many authors opposing governing body recommendations. Regardless of the suggested optimal concentration, there is now growing evidence to suggest that many athletes are in fact Vitamin D deficient, especially in the winter months largely as a consequence of inadequate sun exposure, combined with poor dietary practices, although the consequences of such deficiencies are still unclear in athletic populations. Impaired muscle function and reduced regenerative capacity, impaired immune function, poor bone health and even impaired cardiovascular function have all been associated with low Vitamin D in athletes, however, to date, the majority of studies on Vitamin D have described associations and much more research is now needed examining causation.

A Systems Based Investigation into Vitamin D and Skeletal Muscle Repair, Regeneration and Hypertrophy

Skeletal muscle is a direct target for vitamin D. Observational studies suggest that low 25[OH]D correlates with functional recovery of skeletal muscle following eccentric contractions in humans and crush injury in rats. However, a definitive association is yet to be established. To address this gap in knowledge in relation to damage repair, a randomised, placebo-controlled trial was performed in 20 males with insufficient concentrations of serum 25(OH)D (45 ± 25 nmol/l). Prior to and following 6 wk of supplemental vitamin D3 (4,000 IU/day) or placebo (50 mg of cellulose), participants performed 20 × 10 damaging eccentric contractions of the knee extensors, with peak torque measured over the following 7 days of recovery. Parallel experimentation using isolated human skeletal muscle-derived myoblast cells from biopsies of 14 males with low serum 25(OH)D (37 ± 11 nmol/l) were subjected to mechanical wound injury, which enabled corresponding in vitro studies of muscle repair, regeneration, and hypertrophy in the presence and absence of 10 or 100 nmol 1α,25(OH)2D3. Supplemental vitamin D3 increased serum 25(OH)D and improved recovery of peak torque at 48 h and 7 days postexercise. In vitro, 10 nmol 1α,25(OH)2D3 improved muscle cell migration dynamics and resulted in improved myotube fusion/differentiation at the biochemical, morphological, and molecular level together with increased myotube hypertrophy at 7 and 10 days postdamage. Together, these preliminary data are the first to characterize a role for vitamin D in human skeletal muscle regeneration and suggest that maintaining serum 25(OH)D may be beneficial for enhancing reparative processes and potentially for facilitating subsequent hypertrophy.

l-glutamine Improves Skeletal Muscle Cell Differentiation and Prevents Myotube Atrophy After Cytokine (TNF-α) Stress Via Reduced p38 MAPK Signal Transduction

Tumour Necrosis Factor‐Alpha (TNF‐α) is chronically elevated in conditions where skeletal muscle loss occurs. As l‐glutamine can dampen the effects of inflamed environments, we investigated the role of l‐glutamine in both differentiating C2C12 myoblasts and existing myotubes in the absence/presence of TNF‐α (20 ng · ml−1) ± l‐glutamine (20 mM). TNF‐α reduced the proportion of cells in G1 phase, as well as biochemical (CK activity) and morphological differentiation (myotube number), with corresponding reductions in transcript expression of: Myogenin, Igf‐I, and Igfbp5. Furthermore, when administered to mature myotubes, TNF‐α induced myotube loss and atrophy underpinned by reductions in Myogenin, Igf‐I, Igfbp2, and glutamine synthetase and parallel increases in Fox03, Cfos, p53, and Bid gene expression. Investigation of signaling activity suggested that Akt and ERK1/2 were unchanged, JNK increased (non‐significantly) whereas P38 MAPK substantially and significantly increased in both myoblasts and myotubes in the presence of TNF‐α. Importantly, 20 mM l‐glutamine reduced p38 MAPK activity in TNF‐α conditions back to control levels, with a corresponding rescue of myoblast differentiation and a reversal of atrophy in myotubes. l‐glutamine resulted in upregulation of genes associated with growth and survival including; Myogenin, Igf‐Ir, Myhc2 & 7, Tnfsfr1b, Adra1d, and restored atrophic gene expression of Fox03 back to baseline in TNF‐α conditions. In conclusion, l‐glutamine supplementation rescued suppressed muscle cell differentiation and prevented myotube atrophy in an inflamed environment via regulation of p38 MAPK. l‐glutamine administration could represent an important therapeutic strategy for reducing muscle loss in catabolic diseases and inflamed ageing. J. Cell. Physiol. 9999: 231: 2720–2732, 2016.

Efficacy of High-Dose Vitamin D Supplements for Elite Athletes

Purpose Supplementation with dietary forms of vitamin D is commonplace in clinical medicine, elite athletic cohorts, and the general population, yet the response of all major vitamin D metabolites to high doses of vitamin D is poorly characterized. We aimed to identify the responses of all major vitamin D metabolites to moderate- and high-dose supplemental vitamin D3. Methods A repeated-measures design was implemented in which 46 elite professional European athletes were block randomized based on their basal 25[OH]D concentration into two treatment groups. Athletes received either 35,000 or 70,000 IU·wk−1 vitamin D3 for 12 wk, and 42 athletes completed the trial. Blood samples were collected for 18 wk to monitor the response to supplementation and withdrawal from supplementation. Results Both doses led to significant increases in serum 25[OH]D, and 1,25[OH]2D3. 70,000 IU·wk−1 also resulted in a significant increase of the metabolite 24,25[OH]2D at weeks 6 and 12 that persisted after supplementation withdrawal at week 18, despite a marked decrease in 1,25[OH]2D3. Intact parathyroid hormone was decreased in both groups by week 6 and remained suppressed throughout the trial. Conclusions High-dose vitamin D3 supplementation (70,000 IU·wk−1) may be detrimental for its intended purposes because of increased 24,25[OH]2D production. Rapid withdrawal from high-dose supplementation may inhibit the bioactivity of 1,25[OH]2D3 as a consequence of sustained increases in 24,25[OH]2D that persist as 25[OH]D and 1,25[OH]2D concentrations decrease. These data imply that lower doses of vitamin D3 ingested frequently may be most appropriate and gradual withdrawal from supplementation as opposed to rapid withdrawal may be favorable.

Gonad-related factors promote muscle performance gain during postnatal development in male and female mice

To better define the role of male and female gonad-related factors (MGRF, presumably testosterone, and FGRF, presumably estradiol, respectively) on mouse hindlimb skeletal muscle contractile performance/function gain during postnatal development, we analyzed the effect of castration initiated before puberty in male and female mice. We found that muscle absolute and specific (normalized to muscle weight) maximal forces were decreased in 6-mo-old male and female castrated mice compared with age- and sex-matched intact mice, without alteration in neuromuscular transmission. Moreover, castration decreased absolute and specific maximal powers, another important aspect of muscle performance, in 6-mo-old males, but not in females. Absolute maximal force was similarly reduced by castration in 3-mo-old muscle fiber androgen receptor (AR)-deficient and wild-type male mice, indicating that the effect of MGRF was muscle fiber AR independent. Castration reduced the muscle weight gain in 3-mo mice of both sexes and in 6-mo females but not in males. We also found that bone morphogenetic protein signaling through Smad1/5/9 was not altered by castration in atrophic muscle of 3-mo-old mice of both sexes. Moreover, castration decreased the sexual dimorphism regarding muscle performance. Together, these results demonstrated that in the long term, MGRF and FGRF promote muscle performance gain in mice during postnatal development, independently of muscle growth in males, largely via improving muscle contractile quality (force and power normalized), and that MGFR and FGRF also contribute to sexual dimorphism. However, the mechanisms underlying MGFR and FGRF actions remain to be determined.

Vitamin D and the Athlete: Current Perspectives and New Challenges

The last decade has seen a dramatic increase in general interest in and research into vitamin D, with many athletes now taking vitamin D supplements as part of their everyday dietary regimen. The most recognized role of vitamin D is its regulation of calcium homeostasis; there is a strong relationship between vitamin D and bone health in non-athletic individuals. In contrast, data have consistently failed to demonstrate any relationship between serum 25[OH]D and bone health, which may in part be due to the osteogenic stimulus of exercise. Vitamin D may interact with extra-skeletal tissues such as muscle and the immune system to modulate recovery from damaging exercise and infection risk. Given that many athletes now engage in supplementation, often consuming extreme doses of vitamin D, it is important to assess whether excessive vitamin D can be detrimental to health. It has been argued that toxic effects only occur when serum 25[OH]D concentrations are greater than 180 nmol·l−1, but data from our laboratory have suggested high-dose supplementation could be problematic. Finally, there is a paradoxical relationship between serum 25[OH]D concentration, ethnicity, and markers of bone health: Black athletes often present with low serum 25[OH]D without physiological consequences. One explanation for this could be genetic differences in vitamin D binding protein due to ethnicity, resulting in greater concentrations of bioavailable (or free) vitamin D in some ethnic groups. In the absence of any pathology, screening may be unnecessary and could result in incorrect supplementation. Data must now be re-examined, taking into consideration bioavailable or “free” vitamin D in ethnically diverse groups to enable new thresholds and target concentrations to be established; perhaps, for now, it is time to “set vitamin D free”.

Vitamin D status in chronic fatigue syndrome/myalgic encephalomyelitis: a cohort study from the North-West of England

Objective Severe vitamin D deficiency is a recognised cause of skeletal muscle fatigue and myopathy. The aim of this study was to examine whether chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is associated with altered circulating vitamin D metabolites. Design Cohort study. Setting UK university hospital, recruiting from April 2014 to April 2015. Participants Ninety-two patients with CFS/ME and 94 age-matched healthy controls (HCs). Main outcome measures The presence of a significant association between CFS/ME, fatigue and vitamin D measures. Results No evidence of a deficiency in serum total 25(OH) vitamin D (25(OH)D2 and 25(OH)D3 metabolites) was evident in individuals with CFS/ME. Liquid chromatography tandem mass spectrometry (LC–MS/MS) analysis revealed that total 25(OH)D was significantly higher (p=0.001) in serum of patients with CFS/ME compared with HCs (60.2 and 47.3 nmol/L, respectively). Analysis of food/supplement diaries with WinDiets revealed that the higher total 25(OH) vitamin D concentrations observed in the CFS/ME group were associated with increased vitamin D intake through use of supplements compared with the control group. Analysis of Chalder Fatigue Questionnaire data revealed no association between perceived fatigue and vitamin D levels. Conclusions Low serum concentrations of total 25(OH)D do not appear to be a contributing factor to the level of fatigue of CFS/ME.