Vitamin D

Vitamin D is an essential, fat-soluble vitamin that serves as a precursor steroid to several metabolic and biological processes (Dahlquist 2015). Vitamin D is usually produced by exposure to sunlight, but it can be present in high concentrations in certain foods such as fatty fish and cod liver, egg yolks, and milk (Georgieva 2018). Vitamin D plays a vital role in immune, cardiovascular, and musculoskeletal function and has the potential to increase physical and athletic performance (Kafkalias 2017). 

There is increased interest in supplementing vitamin D since there are reports of deficiencies among athletes, especially those in indoor sports. There is also growing interest in supplementing vitamin D beyond sufficient levels to gain performance enhancing effects. (Powers 2011)

Vitamin D receptors and response elements are found in nearly all tissues in the body, especially skeletal muscle where these receptors are shown to be involved in protein synthesis and muscle growth (Georgieva 2018). Dahlquist (2015) suggested "it is plausible that vitamin D levels above the normal reference range (up to 100 nmol/L) might increase skeletal muscle function, decrease recovery time from training, increase both force and power production, and increase testosterone production, each of which could potentiate athletic performance". 

The potential performance enhancing effects of vitamin D supplementation are primarily demonstrated in populations lacking sufficient levels. Vitamin D supplementation in people who are deficient is effective at improving strength, reducing injury risk, and improving athletic performance. (Abrams 2018) 

There is a lack of evidence supporting the idea that vitamin D supplementation beyond normal levels will have an ergogenic effect. Within sport and athletic populations, adequate vitamin D levels increase muscle strength and physical performance (Georgieva 2018). This suggests that supplementing to reach adequate levels in the case of deficiency may optimize performance. However, in athletes with sufficient vitamin D levels, supplementation is not associated with improvements in athletic performance (Kafkalias 2017). 

For athletes and those highly physically active, vitamin D should be part of daily diet supplementation. The recommended dose to maintain optimum vitamin D levels is 1500-2000 IU/day for adults. (Dahlquist 2015) 

Optimal doses for maximizing athletic performance in populations with already sufficient vitamin D levels have yet to be established. Possible adverse effects with vitamin D include vitamin D toxicity, but there have been no reported cases resulting from exposure to sunlight or regular dietary intake. (Abrams 2018)

In general, vitamin D is associated with performance level, and supplementation to ensure at least adequate levels provides physical improvements. Further research is necessary to evaluate athletic performance improvements with higher doses of vitamin D in athletes who are not deficient. (Abrams 2018)

References

Abrams GD, Feldman D, Safran MR (2018). Effects of Vitamin D on Skeletal Muscle and Athletic Performance. Journal of the American Academy of Orthopaedic Surgeons, 26(8), 278–285.

Dahlquist DT, Dieter BP, Koehle, MS (2015). Plausible ergogenic effects of vitamin D on athletic performance and recovery. Journal of the International Society of Sports Nutrition, 12(1), 33.

Georgieva L, Żołądkiewicz K, Żukow W (2018). Vitamin D concentration effect in health care and sport performance. Journal of Education, Health and Sport, 8(2), 53-70.

Kafkalias A, Stavrou M (2017). Importance of vitamin D in athletes and exercise; A mini review. Arab Journal of Nutrition and Exercise (AJNE), 2(3), 170-9.

Powers S, Nelson WB, Larson-Meyer E (2011). Antioxidant and vitamin D supplements for athletes: Sense or nonsense? Journal of Sports Sciences, 29(sup1), S47-S55.

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