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 .
Conclusion Despite achieving sufficiency in vitamin D concentrations from ≥3000 IU supplementation , physical performance did not significantly improve .
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 r and omized controlled trials ( RCTs ) evaluated the effects of oral vitamin D supplementation on serum 25(OH)D concentrations and physical performance in athletes .
Tibial bone responses to 6-month calcium and vitamin D supplementation in young male jockeys: A randomised controlled trial.
Young male jockeys compromise bone health by engaging in caloric restriction and high volumes of physical activity during periods of musculoskeletal growth and development . The aim of this r and omised , double-blinded , placebo-controlled trial was to establish whether calcium and vitamin D supplementation would improve bone properties of young male jockeys . We conducted a 6-month trial with two groups of weight- , height- and age-matched apprentice male jockeys ( age=20.2 ± 3.2 yrs ) . Participants were supplemented with 800 mg of calcium and 400 IU of vitamin D ( S , n=8 ) or a placebo ( cellulose ) ( P , n=9 ) daily for 6-months . Baseline calcium intake was ( 669.7 ± 274.3 ( S ) vs 790.4 ± 423.9 ( P ) and vitamin D 64.6 ± 19.5 ( S ) vs 81.2 ± 24.4 ( P ) with no statistical differences . Peripheral quantitative computed tomography ( pQCT ) measured ultra-distal ( 4 % ) and proximal ( 66 % ) tibial bone properties at baseline and 6 months . Blood-borne markers of bone turnover , P1NP and CTX and vitamin D concentration were assessed . After co-varying for height , weight and baseline bone measurements , the supplemented group displayed greater post-intervention bone properties at the 66 % proximal site with cortical content ( mgmm ) 6.6 % greater ( p<0.001 ) , cortical area ( mm(2 ) ) 5.9 % larger ( p<0.001 ) , cortical density ( mgcm(2 ) ) 1.3 % greater ( p=0.001 ) , and total area ( mm(2 ) ) 4 % larger ( p=0.003 ) . No other between group differences in bone variables were observed . Blood analysis indicated higher vitamin D levels ( 18.1 % , p=0.014 ) and lower CTx ( ng/L ) ( -24.8 % , p=0.011 ) in the supplemented group with no differences observed in P1NP . This is the first r and omised controlled trial to examine the efficacy of calcium and vitamin D supplementation in improving bone properties in a highly vulnerable , young athletic , weight-restricted population . Results using pQCT indicate beneficial effects of supplementation on bone properties in as little as six months . Although the study size is small , this intervention appears promising as a strategy for improving bone health in young athletes in weight-restricted sports
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 .
Conclusion Despite achieving sufficiency in vitamin D concentrations from ≥3000 IU supplementation , physical performance did not significantly improve .
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 r and omized controlled trials ( RCTs ) evaluated the effects of oral vitamin D supplementation on serum 25(OH)D concentrations and physical performance in athletes .