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 decreases incidence of stress fractures in female navy recruits.
INTRODUCTION Stress fractures ( SFx ) are one of the most common and debilitating overuse injuries seen in military recruits , and they are also problematic for nonmilitary athletic population s. The goal of this r and omized double-blind , placebo-controlled study was to determine whether a calcium and vitamin D intervention could reduce the incidence of SFx in female recruits during basic training . MATERIAL S AND METHODS We recruited 5201 female Navy recruit volunteers and r and omized them to 2000 mg calcium and 800 IU vitamin D/d or placebo .  SFx were ascertained when recruits reported to the Great Lakes clinic with symptoms . All SFx were confirmed with radiography or technetium scan according to the usual Navy protocol . RESULTS A total of 309 subjects were diagnosed with a SFx result ing in an incidence of 5.9 % per 8 wk . Using intention-to-treat analysis by including all enrolled subjects , we found that the calcium and vitamin D group had a 20 % lower incidence of SFx than the control group ( 5.3 % versus 6.6 % , respectively , p = 0.0026 for Fisher 's exact test ) . The per protocol analysis , including only the 3700 recruits who completed the study , found a 21 % lower incidence of fractures in the supplemented versus the control group ( 6.8 % versus 8.6 % , respectively , p = 0.02 for Fisher 's exact test ) . CONCLUSIONS Generalizing the findings to the population of 14,416 women who entered basic training at the Great Lakes during the 24 mo of recruitment , calcium and vitamin D supplementation for the entire cohort would have prevented approximately 187 persons from fracturing . Such a decrease in SFx would be associated with a significant decrease in morbidity and financial costs
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 .