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 .
The Efficacy of Vitamin D Supplementation During a Prolonged Submarine Patrol
Submariners spend prolonged periods submerged without sunlight exposure and may benefit from vitamin D supplementation to maintain vitamin D status . The primary objective of this study was to determine the efficacy of daily vitamin D supplementation on maintenance of 25-hydroxyvitamin D ( 25(OH)D ) during a 3-month submarine patrol . Submariners were r and omly divided into three groups : placebo ( n = 16 ) , 1,000 IU/day ( n = 20 ) , or 2,000 IU/day ( n = 17 ) . Anthropometrics , self-reported dietary calcium and vitamin D intake , serum markers of vitamin D and bone metabolism , and peripheral quantitative computed tomography ( pQCT ) parameters of the tibia were determined before and after the patrol . Prior to departure , 49 % of the subjects were vitamin D insufficient ( < 50 nmol/L ) . Following the patrol , 25(OH)D increased in all groups ( p < 0.001 ) : 3.3 ± 13.1 ( placebo ) , 4.6 ± 11.3 ( 1,000 IU/day ) , and 13 ± 14 nmol/L ( 2,000 IU/day ) . The changes in 25(OH)D levels were dependent upon the baseline concentration of 25(OH)D and body mass ( p < 0.001 ) . Osteocalcin increased by 38 % ( p < 0.01 ) , and pQCT analyses revealed small , yet significant increases in indices of tibial structure and strength ( p < 0.05 ) that were independent of supplementation . These data suggest that vitamin D status was low prior to the patrol , and the subsequent changes in vitamin D status were dependent on the baseline 25(OH)D levels and body mass . Furthermore , short-term skeletal health does not appear to be negatively affected by 3 months of submergence in spite of a suboptimal response to vitamin D supplementation
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 .