title: Vitamin D Supplementation and Physical Performance in Adolescent Swimmers. Monthly High-Dose Vitamin D Treatment for the Prevention of Functional Decline: A Randomized Clinical Trial. Vitamin D3 Supplementation Does Not Improve Sprint Performance in Professional Rugby Players: A Randomized, Placebo-Controlled, Double-Blind Intervention Study. Annual high-dose oral vitamin D and falls and fractures in older women: a randomized controlled trial. Increased Velocity Exercise Specific to Task (InVEST) training: a pilot study exploring effects on leg power, balance, and mobility in community-dwelling older women. Supplementation with High Doses of Vitamin D to Subjects without Vitamin D Deficiency May Have Negative Effects: Pooled Data from Four Intervention Trials in Tromsø Low-Dose Vitamin D Prevents Muscular Atrophy and Reduces Falls and Hip Fractures in Women after Stroke: A Randomized Controlled Trial The Delphi list: a criteria list for quality assessment of randomized clinical trials for conducting systematic reviews developed by Delphi consensus. Low vitamin D and high parathyroid hormone levels as determinants of loss of muscle strength and muscle mass (sarcopenia): the Longitudinal Aging Study Amsterdam. Improving the vitamin D status of vitamin D deficient adults is associated with improved mitochondrial oxidative function in skeletal muscle. Reliability of the PEDro scale for rating quality of randomized controlled trials. The effects of vitamin D3 supplementation on serum total 25[OH]D concentration and physical performance: a randomised dose–response study Acute Effects of Vitamin D3 Supplementation on Muscle Strength in Judoka Athletes: A Randomized Placebo-Controlled, Double-Blind Trial Influence of vitamin D mushroom powder supplementation on exercise-induced muscle damage in vitamin D insufficient high school athletes A randomized study on the effect of vitamin D₃ supplementation on skeletal muscle morphology and vitamin D receptor concentration in older women.
abstract: It is hypothesized that vitamin D insufficiency in athletes might negatively affect sport performance . The objective of this study was to examine the effect of vitamin D3 supplementation on physical performance of adolescent swimmers with vitamin D insufficiency . Fifty-three adolescent competitive swimmers with vitamin D insufficiency ( serum 25-hydroxyvitamin-D concentrations ( 25(OH)D ) < 30 ng/ml , mean 24.2 ± 4.8 ng/ml ) were r and omized to receive 2,000 IU/day of vitamin D3 or placebo for 12 weeks . Swimming performance at several speeds , arm-grip strength , and one-legged balance , were measured before and after supplementation . The age-adjusted changes in performance variables during the study were compared between groups . 25(OH ) D concentrations at study end were significantly higher in the vitamin group compared with the placebo group ( 29.6 ± 6.5 ng/ml vs. 20.3 ± 4.2 ng/ml , p < .001 ) , yet only 48 % of the vitamin group became vitamin D sufficient with this dosing . No between-group differences were found in the changes of the performance variables tested . No significant differences in performance were found between participants that became vitamin D sufficient , and those who did not . No significant correlation was found between the change in serum 25(OH)D and age-adjusted balance , strength or swimming performance at study end . Vitamin D3 supplementation that raised serum 25(OH)D concentrations by a mean of 9.3 ng/ml above placebo in adolescent swimmers with vitamin D insufficiency , did not improve physical performance more than placebo IMPORTANCE Vitamin D deficiency has been associated with poor physical performance . OBJECTIVE To determine the effectiveness of high-dose vitamin D in lowering the risk of functional decline . DESIGN , SETTING , AND PARTICIPANTS One-year , double-blind , r and omized clinical trial conducted in Zurich , Switzerl and . The screening phase was December 1 , 2009 , to May 31 , 2010 , and the last study visit was in May 2011 . The date s of our analysis were June 15 , 2012 , to October 10 , 2015 . Participants were 200 community-dwelling men and women 70 years and older with a prior fall . INTERVENTIONS Three study groups with monthly treatments , including a low-dose control group receiving 24,000 IU of vitamin D3 ( 24,000 IU group ) , a group receiving 60,000 IU of vitamin D3 ( 60,000 IU group ) , and a group receiving 24,000 IU of vitamin D3 plus 300 μg of calcifediol ( 24,000 IU plus calcifediol group ) . MAIN OUTCOMES AND MEASURES The primary end point was improving lower extremity function ( on the Short Physical Performance Battery ) and achieving 25-hydroxyvitamin D levels of at least 30 ng/mL at 6 and 12 months . A secondary end point was monthly reported falls . Analyses were adjusted for age , sex , and body mass index . RESULTS The study cohort comprised 200 participants ( men and women ≥ 70 years with a prior fall ) . Their mean age was 78 years , 67.0 % ( 134 of 200 ) were female , and 58.0 % ( 116 of 200 ) were vitamin D deficient ( < 20 ng/mL ) at baseline . Intent-to-treat analyses showed that , while 60,000 IU and 24,000 IU plus calcifediol were more likely than 24,000 IU to result in 25-hydroxyvitamin D levels of at least 30 ng/mL ( P = .001 ) , they were not more effective in improving lower extremity function , which did not differ among the treatment groups ( P = .26 ) . However , over the 12-month follow-up , the incidence of falls differed significantly among the treatment groups , with higher incidences in the 60,000 IU group ( 66.9 % ; 95 % CI , 54.4 % to 77.5 % ) and the 24,000 IU plus calcifediol group ( 66.1 % ; 95 % CI , 53.5%-76.8 % ) group compared with the 24,000 IU group ( 47.9 % ; 95 % CI , 35.8%-60.3 % ) ( P = .048 ) . Consistent with the incidence of falls , the mean number of falls differed marginally by treatment group . The 60,000 IU group ( mean , 1.47 ) and the 24,000 IU plus calcifediol group ( mean , 1.24 ) had higher mean numbers of falls compared with the 24,000 IU group ( mean , 0.94 ) ( P = .09 ) . CONCLUSIONS AND RELEVANCE Although higher monthly doses of vitamin D were effective in reaching a threshold of at least 30 ng/mL of 25-hydroxyvitamin D , they had no benefit on lower extremity function and were associated with increased risk of falls compared with 24,000 IU . TRIAL REGISTRATION clinical trials.gov Identifier : NCT01017354 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 prospect i ve r and omized controlled trials with adequate statistical power to test this relationship , and none in the southern hemisphere . Thus , a prospect i ve double-blind , r and omized , placebo-controlled intervention trial was conducted involving 57 professional rugby union players in New Zeal and . Participants were r and omized 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 CONTEXT Improving vitamin D status may be an important modifiable risk factor to reduce falls and fractures ; however , adherence to daily supplementation is typically poor . OBJECTIVE To determine whether a single annual dose of 500,000 IU of cholecalciferol administered orally to older women in autumn or winter would improve adherence and reduce the risk of falls and fracture . DESIGN , SETTING , AND PARTICIPANTS A double-blind , placebo-controlled trial of 2256 community-dwelling women , aged 70 years or older , considered to be at high risk of fracture were recruited from June 2003 to June 2005 and were r and omly assigned to receive cholecalciferol or placebo each autumn to winter for 3 to 5 years . The study concluded in 2008 . INTERVENTION 500,000 IU of cholecalciferol or placebo . MAIN OUTCOME MEASURES Falls and fractures were ascertained using monthly calendars ; details were confirmed by telephone interview . Fractures were radiologically confirmed . In a sub study , 137 r and omly selected participants underwent serial blood sampling for 25-hydroxycholecalciferol and parathyroid hormone levels . RESULTS Women in the cholecalciferol ( vitamin D ) group had 171 fractures vs 135 in the placebo group ; 837 women in the vitamin D group fell 2892 times ( rate , 83.4 per 100 person-years ) while 769 women in the placebo group fell 2512 times ( rate , 72.7 per 100 person-years ; incidence rate ratio [ RR ] , 1.15 ; 95 % confidence interval [ CI ] , 1.02 - 1.30 ; P = .03 ) . The incidence RR for fracture in the vitamin D group was 1.26 ( 95 % CI , 1.00 - 1.59 ; P = .047 ) vs the placebo group ( rates per 100 person-years , 4.9 vitamin D vs 3.9 placebo ) . A temporal pattern was observed in a post hoc analysis of falls . The incidence RR of falling in the vitamin D group vs the placebo group was 1.31 in the first 3 months after dosing and 1.13 during the following 9 months ( test for homogeneity ; P = .02 ) . In the sub study , the median baseline serum 25-hydroxycholecalciferol was 49 nmol/L. Less than 3 % of the sub study participants had 25-hydroxycholecalciferol levels lower than 25 nmol/L. In the vitamin D group , 25-hydroxycholecalciferol levels increased at 1 month after dosing to approximately 120 nmol/L , were approximately 90 nmol/L at 3 months , and remained higher than the placebo group 12 months after dosing . CONCLUSION Among older community-dwelling women , annual oral administration of high-dose cholecalciferol result ed in an increased risk of falls and fractures . TRIAL REGISTRATION anzctr.org.au Identifier : ACTRN12605000658617 ; is rct n.org Identifier : IS RCT N83409867 OBJECTIVES To evaluate a dynamic form of weighted vest exercise suitable for home use and design ed to enhance muscle power , balance , and mobility . DESIGN A single-blind , r and omized , controlled trial . SETTING Outpatient exercise research facility situated within an academic long-term care center . PARTICIPANTS Twenty-one community-dwelling women aged 70 and older with a Short Physical Performance Battery ( SPPB ) score between 4 and 10 ( out of 12 ) . INTERVENTIONS Subjects were r and omized into a progressive resistance-training program using weighted vests for resistance with exercises design ed to be specific to mobility tasks and have a component performed at the fastest possible velocity ( Increased Velocity Exercise Specific to Task ( InVEST ) , n=11 ) or a control exercise group ( control , n=10 ) , which performed slow-velocity , low-resistance exercise . Both groups exercised three times a week for 12 weeks . MEASUREMENTS Changes in muscle power , balance , and physical performance were compared . RESULTS In comparison to control group , InVEST group manifested significant improvements ( P<.05 ) in leg power across measurements obtained at 75 % to 90 % of the one-repetition maximum . Both groups demonstrated significant improvements in chair st and and SPPB score from baseline , and the InVEST group showed significant improvements in gait speed and chair st and from baseline ( P<.05 ) . InVEST produced significantly greater changes in chair st and time than control ( P<.05 ) . CONCLUSION InVEST training appears be an effective means of enhancing leg power and chair rise in this population and is worthy of further investigation as a means of enhancing balance and mobility Data were pooled from four r and omized clinical trials with vitamin D performed in Tromsø with weight reduction , insulin sensitivity , bone density , and depression scores as endpoints . Serum lipids , glycated hemoglobin ( HbA1c ) , and high sensitivity C-Reactive Protein , ( HS-CRP ) were measured at baseline and after 6–12 months of supplementation with vitamin D 20 000 IU–40 000 IU per week versus placebo .  A total of 928 subjects who completed the interventions were included . At baseline the mean serum 25-hydroxyvitamin D ( 25(OH)D ) level in those given vitamin D was 55.9 ( 20.9 ) nmol/L and the mean increase was 82.4 ( 40.1 ) nmol/L. Compared with the placebo group there was in the vitamin D group at the end of the studies a slight , but significant , increase in HbA1c of 0.04 % , an increase in HS-CRP of 0.07 mg/L in those with serum 25(OH)D < 50 nmol/L , and in those with low baseline HDL-C and serum 25(OH)D < 50 nmol/L a slight decrease serum HDL-C of 0.08 mmol/L ( P < 0.05 ) . No serious side-effects were seen . In conclusion , in subjects without vitamin D deficiency , there is no improvement in serum lipids , HbA1c , or HS-CRP with high dose vitamin D supplementation . If anything , the effect is negative OBJECTIVE Vitamin D supplementation is suggested to reduce the risk of falls among ambulatory or institutionalized elderly subjects . The present study was undertaken to address the reduced risk of falls and hip fractures in patients with long-st and ing stroke by vitamin D supplementation . METHODS Ninety-six elderly women with poststroke hemiplegia were followed for two years . Patients were r and omly assigned to one of the two groups , and 48 patients received 1,000 IU ergocalciferol daily , and the remaining 48 received placebo . The number of falls per person and incidence of hip fractures were compared between the two groups . Strength and tissue ATPase of skeletal muscles on the nonparetic side were assessed before and after the study . RESULTS At baseline , serum 25-hydroxyvitamin D levels were in the deficient range ( < 10 ng/ml ) in all patients ; and vitamin D treatment enhanced serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels .  Vitamin D treatment accounted for a 59 % reduction in falls ( 95 % CI , 28 - 81 % ; p = 0.003 ) . There were increases in the relative number and size of type II muscle fibers and improved muscle strength in the vitamin D-treated group . Hip fractures occurred in 4 of 48 placebo group and 0 in 48 vitamin D2 group during the 2-year study period ( log-rank , p = 0.049 ) . CONCLUSION Vitamin D may increase muscle strength by improving atrophy of type II muscle fibers , which may lead to decreased falls and hip fractures Most systematic review s rely substantially on the assessment of the method ological quality of the individual trials . The aim of this study was to obtain consensus among experts about a set of generic core items for quality assessment of r and omized clinical trials ( RCTs ) . The invited participants were experts in the field of quality assessment of RCTs . The initial item pool contained all items from existing criteria lists . Subsequently , we reduced the number of items by using the Delphi consensus technique . Each Delphi round comprised a question naire , an analysis , and a feedback report . The feedback report included staff team decisions made on the basis of the analysis and their justification . A total of 33 international experts agreed to participate , of whom 21 completed all question naires . The initial item pool of 206 items was reduced to 9 items in three Delphi rounds . The final criteria list ( the Delphi list ) was satisfactory to all participants . It is a starting point on the way to a minimum reference st and ard for RCTs on many different research topics . This list is not intended to replace , but rather to be used alongside , existing criteria lists The age-related change in hormone concentrations has been hypothesized to play a role in the loss of muscle mass and muscle strength with aging , also called sarcopenia . The aim of this prospect i ve study was to investigate whether low serum 25-hydroxyvitamin D ( 25-OHD ) and high serum PTH concentration were associated with sarcopenia . In men and women aged 65 yr and older , participants of the Longitudinal Aging Study Amsterdam , grip strength ( n = 1008 ) and appendicular skeletal muscle mass ( n = 331 , using dual-energy x-ray absorptiometry ) were measured in 1995 - 1996 and after a 3-yr follow-up . Sarcopenia was defined as the lowest sex-specific 15th percentile of the cohort , translating into a loss of grip strength greater than 40 % or a loss of muscle mass greater than 3 % . After adjustment for physical activity level , season of data collection , serum creatinine concentration , chronic disease , smoking , and body mass index , persons with low ( < 25 nmol/liter ) baseline 25-OHD levels were 2.57 ( 95 % confidence interval 1.40 - 4.70 , based on grip strength ) and 2.14 ( 0.73 - 6.33 , based on muscle mass ) times more likely to experience sarcopenia , compared with those with high ( > 50 nmol/liter ) levels . High PTH levels ( > or=4.0 pmol/liter ) were associated with an increased risk of sarcopenia , compared with low PTH ( < 3.0 pmol/liter ) : odds ratio = 1.71 ( 1.07 - 2.73 ) based on grip strength , odds ratio = 2.35 ( 1.05 - 5.28 ) based on muscle mass . The associations were similar in men and women . The results of this prospect i ve , population -based study show that lower  25-OHD  and higher  PTH levels increase the risk of sarcopenia in older men and women OBJECTIVE Suboptimal mitochondrial function has been implicated in several disorders in which fatigue is a prominent feature . Vitamin D deficiency is a well-recognized cause of fatigue and myopathy . The aim of this study was to examine the effects of cholecalciferol therapy on skeletal mitochondrial oxidative function in symptomatic , vitamin D-deficient individuals . DESIGN This longitudinal study assessed mitochondrial oxidative phosphorylation in the gastrosoleus compartment using phosphorus-31 magnetic resonance spectroscopy measurements of phosphocreatine recovery kinetics in 12 symptomatic , severely vitamin D-deficient subjects before and after treatment with cholecalciferol .  All subjects had serum assays before and after cholecalciferol therapy to document serum 25-hydroxyvitamin D ( 25OHD ) and bone profiles . Fifteen healthy controls also underwent (31)P-magnetic resonance spectroscopy and serum 25OHD assessment . RESULTS The phosphocreatine recovery half-time ( τ1/2PCr ) was significantly reduced after cholecalciferol therapy in the subjects indicating an improvement in maximal oxidative phosphorylation ( 34.44 ± 8.18 sec to 27.84 ± 9.54 sec , P < .001 ) . This was associated with an improvement in mean serum 25OHD levels ( 8.8 ± 4.2 nmol/L to 113.8 ± 51.5 nmol/L , P < .001 ) . There was no difference in phosphate metabolites at rest . A linear regression model showed that decreasing serum 25OHD levels was associated with increasing τ1/2PCr ( r = -0.41 , P = .009 ) . All patients reported an improvement in fatigue  after cholecalciferol therapy . CONCLUSIONS Cholecalciferol therapy augments muscle mitochondrial maximal oxidative phosphorylation after exercise in symptomatic , vitamin D-deficient individuals . This finding suggests that changes in mitochondrial oxidative phosphorylation in skeletal muscle could at least be partly responsible for the fatigue experienced by these patients . For the first time , we demonstrate a link between vitamin D and the mitochondria in human skeletal muscle BACKGROUND AND PURPOSE Assessment of the quality of r and omized controlled trials ( RCTs ) is common practice in systematic review s. However , the reliability of data obtained with most quality assessment scales has not been established . This report describes 2 studies design ed to investigate the reliability of data obtained with the Physiotherapy Evidence Data base ( PEDro ) scale developed to rate the quality of RCTs evaluating physical therapist interventions . METHOD In the first study , 11 raters independently rated 25 RCTs r and omly selected from the PEDro data base . In the second study , 2 raters rated 120 RCTs r and omly selected from the PEDro data base , and disagreements were resolved by a third rater ; this generated a set of individual rater and consensus ratings . The process was repeated by independent raters to create a second set of individual and consensus ratings . Reliability of ratings of PEDro scale items was calculated using multirater kappas , and reliability of the total ( summed ) score was calculated using intraclass correlation coefficients ( ICC [ 1,1 ] ) . RESULTS The kappa value for each of the 11 items ranged from.36 to.80 for individual assessors and from.50 to.79 for consensus ratings generated by groups of 2 or 3 raters . The ICC for the total score was.56 ( 95 % confidence interval=.47-.65 ) for ratings by individuals , and the ICC for consensus ratings was.68 ( 95 % confidence interval=.57-.76 ) . DISCUSSION AND CONCLUSION The reliability of ratings of PEDro scale items varied from " fair " to " substantial , " and the reliability of the total PEDro score was " fair " to " good . Background Vitamin D deficiency is common in the general public and athletic population s 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 r and omised ( 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 Objective : Indoor athletes have been shown to be prone to vitamin D3 deficiency . The aim of the study was to examine the acute effects of vitamin D supplementation on muscle function using isokinetic dynamometry . Design : R and omized placebo-controlled , double-blind study . Setting : Institutional . Participants : Adult male white national level judoka athletes ( n = 22 ) who were involved in full-time training . Exclusion criteria were vitamin supplementation , overseas travel to sunny climes , and /or an injury incurred during the last 3 months before testing . Interventions : Subjects were r and omly allocated to the treatment ( 150 000IU vitamin D3 ) or placebo and given blinded supplements by an independent research er . Participants were tested twice , 8 days apart , on a Monday morning before the start of judo training and after 2 days of rest . A 5 to 7 mL of blood sample was collected followed by isokinetic concentric quadriceps and hamstring muscle function assessment s on the right leg at 30 and 200 ° ·s−1 . Main Outcome Measures : Repeated- measures analysis of variance was used to analyze isokinetic muscle force and serum 25(OH)D3 . Regression to the mean was used to examine changes in 25(OH)D3 levels over the study period . Results : The treatment group demonstrated a significant increase in serum 25(OH)D levels ( 34 % , P ⩽ 0.001 ) and muscle strength ( 13 % , P = 0.01 ) between days 1 and 8 . No significant differences were found for the placebo group for the same period . Conclusions : A single bolus of 150 000IU vitamin D3 had a significant positive effect on serum 25(OH)D levels and muscle function in vitamin D insufficient elite indoor athletes . Clinical Relevance : Serum 25(OH)D3 levels of indoor athletes should be monitored throughout the year and especially during winter months . Beneficial responses , in muscle strength and serum 25(OH)D3 , to 1 dose of vitamin D3 supplementation can be observed within 1 week of ingestion . Muscle strength is linked to serum 25(OH)D levels Abstract Incidence of vitamin D deficiency is increasing worldwide . The purpose of this study was to determine if supplementation with vitamin D2 from Portobello mushroom powder would enhance skeletal muscle function and attenuate exercise-induced muscle damage in low vitamin D status high school athletes . Participants were r and omised to Portobello mushroom powder ( 600 IU/d vitamin D2 ) or placebo for 6 weeks . Participants then completed a 1.5-h exercise session design ed to induce skeletal muscle damage . Blood sample s and measures of skeletal muscle function were taken pre-supplementation , post-supplementation/pre-exercise and post-exercise . Six weeks supplementation with vitamin D2 increased serum 25(OH)D2 by 9.9-fold and decreased serum 25(OH)D3 by 28 % . Changes in skeletal muscle function and circulating markers of skeletal muscle damage did not differ between groups . In conclusion , 600 IU/d vitamin D2 increased 25(OH)D2 with a concomitant decrease in 25(OD)D3 , with no effect on muscular function or exercise-induced muscle damage in high school athletes CONTEXT Studies examining whether vitamin D supplementation increases muscle mass or muscle-specific vitamin D receptor ( VDR ) concentration are lacking . OBJECTIVE Our objective was to determine whether vitamin D₃ 4000 IU/d alters muscle fiber cross-sectional area ( FCSA ) and intramyonuclear VDR concentration over 4 months . DESIGN AND SETTING This was a r and omized , double-blind , placebo-controlled study in a single center . PARTICIPANTS Participants were 21 mobility-limited women ( aged ≥ 65 years ) with serum 25-hydroxyvitamin D ( 25OHD ) levels of 22.5 to 60 nmol/L. MAIN OUTCOME MEASURES Baseline and 4-month FCSA and intramyonuclear VDR were measured from vastus lateralis muscle cross-sections probed for muscle fiber type ( I/IIa/IIx ) and VDR using immunofluorescence . RESULTS At baseline , mean ( ±SD ) age was 78 ± 5 years ; body mass index was 27 ± 5 kg/m² , 25OHD was 46.3 ± 9.5 nmol/L , and  a short physical performance battery score was 7.95 ± 1.57 out of 12 . At 4 months , 25OHD level was 52.5 ± 17.1 ( placebo ) vs 80.0 ± 11.5 nmol/L ( vitamin D [ VD ] ; P < .01 ) , and change in 25OHD level was strongly associated with percent change in intramyonuclear VDR concentration-independent of group ( r = 0.87 , P < .001 ) . By treatment group , percent change in intramyonuclear VDR concentration was 7.8 % ± 18.2 % ( placebo ) vs 29.7 % ± 11.7 % ( VD ; P = .03 ) with a more pronounced group difference in type II vs I fibers . Percent change in total ( type I/II ) FCSA was -7.4 % ± 18.9 % ( placebo ) vs 10.6 % ± 20.0 % ( VD ; P = .048 ) . CONCLUSION Vitamin D₃ supplementation  increased intramyonuclear VDR concentration by 30 % and increased muscle fiber size by 10 % in older , mobility-limited , vitamin D-insufficient women . Further work is needed to determine whether the observed effect of vitamin D on fiber size is mediated by the VDR and to identify which signaling pathways are involved
target: 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 .
background: 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 aim ed 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 .