Conclusion Despite the limitations of the current evidence , the prevalence of vitamin D inadequacy in athletes is prominent .
The risk significantly increases in higher latitudes , in winter and early spring seasons , and for indoor sport activities .
The prevalence of injuries in athletes is notable but its association with  vitamin D status is unclear .
Background Vitamin D is essential for maintaining optimal bone health .
The prevalence of vitamin D inadequacy in athletes is currently unclear .
Objective The objective of this study is to determine the prevalence of vitamin D inadequacy in athletes .
Serum 25(OH)D is measured to clinical ly determine vitamin D status .
The effects of vitamin D3 supplementation on serum total 25[OH]D concentration and physical performance: a randomised dose–response study
Background Vitamin D deficiency is common in the general public and athletic population s and may impair skeletal muscle function . We therefore assessed the effects of vitamin D3 supplementation on serum 25[OH]D concentrations and physical performance . Methods 30 club-level athletes were block r and omised ( using baseline 25[OH]D concentrations ) into one of three groups receiving either a placebo ( PLB ) , 20 000 or 40 000 IU/week oral vitamin D3 for 12 weeks . Serum 25[OH]D and muscle function ( 1-RM bench press and leg press and vertical jump height ) were measured presupplementation , 6 and 12 weeks postsupplementation . Vitamin D deficiency was defined in accordance with the US Institute of Medicine guideline ( < 50 nmol/l ) . Results 57 % of the subject population were vitamin D deficient at baseline ( mean±SD value 51±24 nmol/l ) . Following 6 and 12 weeks supplementation with 20 000 IU ( 79±14 and 85±10 nmol/l , respectively ) or 40 000 IU vitamin D3 ( 98±14 and 91±24 nmol/l , respectively ) , serum vitamin D concentrations increased in all participants , with every individual achieving concentrations greater than 50 nmol/l . In contrast , vitamin D concentration in the PLB group decreased at 6 and 12 weeks ( 37±18 and 41±22 nmol/l , respectively ) . Increasing serum 25[OH]D had no significant effect on any physical performance parameter ( p>0.05 ) . Conclusions Both 20 000 and 40 000 IU vitamin D3 supplementation over a 6-week period elevates serum 25[OH]D concentrations above 50 nmol/l , but neither dose given for 12 weeks improved our chosen measures of physical performance
Conclusion Despite the limitations of the current evidence , the prevalence of vitamin D inadequacy in athletes is prominent .
The risk significantly increases in higher latitudes , in winter and early spring seasons , and for indoor sport activities .
The prevalence of injuries in athletes is notable but its association with  vitamin D status is unclear .
Background Vitamin D is essential for maintaining optimal bone health .
The prevalence of vitamin D inadequacy in athletes is currently unclear .
Objective The objective of this study is to determine the prevalence of vitamin D inadequacy in athletes .
Serum 25(OH)D is measured to clinical ly determine vitamin D status .