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 .
Calcium and vitamin D supplementation maintains parathyroid hormone and improves bone density during initial military training: a randomized, double-blind, placebo controlled trial.
Calcium and vitamin D are essential nutrients for bone health . Periods of activity with repetitive mechanical loading , such as military training , may result in increases in parathyroid hormone ( PTH ) , a key regulator of Ca metabolism , and may be linked to the development of stress fractures . Previous studies indicate that consumption of a Ca and vitamin D supplement may reduce stress fracture risk in female military personnel during initial military training , but circulating markers of Ca and bone metabolism and measures of bone density and strength have not been determined . This r and omized , double-blind , placebo-controlled trial sought to determine the effects of providing supplemental Ca and vitamin D ( Ca+Vit D , 2000 mg and 1000IU/d , respectively ) , delivered as 2 snack bars per day throughout 9weeks of Army initial military training ( or basic combat training , BCT ) on PTH , vitamin D status , and measures of bone density and strength in personnel undergoing BCT , as well as independent effects of BCT on bone parameters . A total of 156 men and 87 women enrolled in Army BCT ( Fort Sill , OK ; 34.7 ° N latitude ) volunteered for this study . Anthropometric , biochemical , and dietary intake data were collected pre- and post-BCT . In addition , peripheral quantitative computed tomography was utilized to assess tibia bone density and strength in a subset of volunteers ( n=46 ) . Consumption of supplemental Ca+Vit D  increased circulating ionized Ca ( group-by-time , P=0.022 ) , maintained PTH ( group-by-time , P=0.032 ) , and increased the osteoprotegerin : RANKL ratio ( group-by-time , P=0.006 ) . Consistent with the biochemical markers , Ca+Vit D  improved vBMD ( group-by-time , P=0.024 ) at the 4 % site and cortical BMC ( group-by-time , P=0.028 ) and thickness ( group-by-time , P=0.013 ) at the 14 % site compared to placebo . These data demonstrate the benefit of supplemental Ca and vitamin D for maintaining bone health during periods of elevated bone turnover , such as initial military training . This trial was registered with ClincialTrials.gov , NCT01617109
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 .