Vitamin D and Athletic Performance

I recently wrote a paper on Vitamin D and its impact on athletic performance and rather than share the entire paper, I thought I would just share with you the important excerpts on why Vitamin D is so important to us and why most people are deficient.  
With a growing body of research on Vitamin D and its deficiency in the population, have come new recommendations on intake for the average healthy population.  With these new recommendations, have come questions about its implications for athletes and its role in athletic performance.  While studies linking vitamin D and athletes are somewhat scarce, the most recent studies suggest that vitamin D acts more like a hormone than a vitamin and therefore the new recommendations have new implications on health, hormone function and supplementation.  Because most people are deficient in vitamin D, the use of supplements is almost necessary for most people who are not exposed to direct sunlight for 10-15 minutes per day or restrict vitamin D containing foods, i.e. milk, eggs, cold water fish.  Translating that to athletes who train indoors, wear sunscreen or who restrict their diet, athletes may or may not have a greater need for vitamin D in relation to the general population.  

The most notable function of calcitriol is that of its steroid hormone-like properties.  The major function of vitamin D plays is that of gene transcription for specific mRNA proteins including calbindin or calcium-binding protein.¹  Via gene expression vitamin D plays a large role in the absorption of calcium and phosphorous in the intestines.  In a separate mechanism, which is not well understood vitamin D is capable of opening calcium channels, as well as aiding in the stimulation of enzymes that encourage phosphorous absorption.¹ 

Because vitamin D plays an integral role in calcium absorption from the small intestine, vitamin D it is also seen as crucial to muscle function.²  Calcium contributes to two regulatory processes in skeletal muscle, the link between excitation and contraction and the activation of cellular enzymes linked to energy production.²  The availability of calcium is crucial to the converting of electrical signals from the brain to the skeletal muscle.  Once the signal is interpreted across the cell membrane it is able to stimulate the actin and myosin fibers in the muscle to interact.²  Research has suggested that fatigue during high intensity exercise can be linked to the cell’s calcium-handling capacity.²  

So the question remains, is vitamin D supplementation needed for all athletes given the growing statistics that most of the population is vitamin D deficient?  Most experts agree that vitamin D status effects bone and muscle health and more recently immune function and the mediation of inflammation.  Current guidelines for vitamin D supplementation are set at 200IU for children and adults up to 50 years of age, 400 IU for adults 51-70 years of age, and 600IU for adults over the age of 71.⁶  Based on current research and the prevalence of vitamin D insufficiency in the general population, it may be concluded that current recommendation are inadequate.⁶ Bischoff-Ferrari et al., have recently recommended supplementation levels between 600-1000 IU/day for individuals of all ages who are lacking sun exposure.⁶

References

1.            Mahan LK, Escott-Stump S. Krause's food & nutrition therapy. 12th ed. St. Louis, Mo.: Saunders/Elsevier; 2008.

2.            Maughan RJ, IOC Medical Commission., International Federation of Sports Medicine. Nutrition in sport. Osney Mead, Oxford ; Malden, MA: Blackwell Science; 2000.

3.            Schubert L, DeLuca HF. Hypophosphatemia is responsible for skeletal muscle weakness of vitamin D deficiency. Archives of Biochemistry and Biophysics. Aug 15 2010;500(2):157-161.

4.            Fioletov VE, McArthur LJ, Mathews TW, Marrett L. Estimated ultraviolet exposure levels for a sufficient vitamin D status in North America. Journal of Photochemistry and Photobiology B. Aug 2 2010;100(2):57-66.

5.            Cannell JJ, Hollis BW, Sorenson MB, Taft TN, Anderson JJ. Athletic performance and vitamin D. Medicine and Science in Sports and Exercise. May 2009;41(5):1102-1110.

6.            Willis KS, Peterson NJ, Larson-Meyer DE. Should we be concerned about the vitamin D status of athletes? International Journal of Sport Nutrition and Exercise Metabolism. Apr 2008;18(2):204-224.

7.            Hamilton B. Vitamin D and human skeletal muscle. Scandinavian Journal of Medicine and Science in Sports. Apr 2010;20(2):182-190.

8.            Holick MF. The vitamin D epidemic and its health consequences. American Journal of Clinical Nutrition. Nov 2005;135(11):2739S-2748S.

9.            Pepper KJ, Judd SE, Nanes MS, Tangpricha V. Evaluation of vitamin D repletion regimens to correct vitamin D status in adults. Endocrine Practice. Mar 2009;15(2):95-103.

10.          Dawson-Hughes B, Heaney RP, Holick MF, Lips P, Meunier PJ, Vieth R. Estimates of optimal vitamin D status. Osteoporosis International. Jul 2005;16(7):713-716.

11.          Williams MH. Dietary supplements and sports performance: minerals. Journal of the International Society of Sports Nutrition. 2005;2:43-49.

12.          Williams MH. Dietary supplements and sports performance: introduction and vitamins. Journal of the International Society of Sports Nutrition. 2004;1:1-6.