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 effect of 14 weeks of vitamin D3 supplementation on antimicrobial peptides and proteins in athletes
Abstract Heavy training is associated with increased respiratory infection risk and antimicrobial proteins are important in defence against oral and respiratory tract infections . We examined the effect of 14 weeks of vitamin D3 supplementation ( 5000 IU/day ) on the resting plasma cathelicidin concentration and the salivary secretion rates of secretory immunoglobulin A ( SIgA ) , cathelicidin , lactoferrin and lysozyme in athletes during a winter training period .  Blood and saliva were obtained at the start of the study from 39 healthy men who were r and omly allocated to vitamin D3 supplement or placebo .  Blood sample s were also collected at the end of the study ; saliva sample s were collected after 7 and 14 weeks . Plasma total 25(OH)D concentration increased by 130 % in the vitamin D3 group and decreased by 43 % in the placebo group ( both P = 0.001 ) . The percentage change of plasma cathelicidin concentration in the vitamin D3 group was higher than in the placebo group ( P = 0.025 ) . Only in the vitamin D3 group , the saliva SIgA and cathelicidin secretion rates increased over time ( both P = 0.03 ) . A daily 5000 IU vitamin D3 supplement has a beneficial effect in up-regulating the expression of SIgA and cathelicidin in athletes during a winter training period , which could improve resistance to respiratory infections
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 .