Overview of Vitamin D and Synthesis
The Science in Sport Vitamin D3 is formulated with 5000iu vitamin D3 per serving. Vitamin D is a fat-soluble vitamin with two compounds in this group, ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamins D2 and D3 can be thought of as prohormones, in that they have no significant bioactivity until converted into their active form (1,25[OH]D), that displays the same characteristics as a hormone. The beneficial effects of vitamin D depends on the subsequent availability of blood 25[OH]D; therefore, the goal of supplementation should be to correct any deficiencies and raise blood 25[OH]D levels to normal values. Vitamin D3 supplementation is thought of to be more effective at raising blood 25[OH]D levels compared to vitamin D2 (1), meaning that this specific form is the one to look for when choosing a supplement.
Why Supplement with Vitamin D3?
Through exposure to the sun and synthesis via the skin, our body can naturally produce vitamin D3. However, vitamin D3 deficiency is common in both the general public and athletic populations (2). This may be due to: living at far northern or southern latitudes, training indoors, protective clothing, sun-screen or consciously avoiding sun exposure. All of these factors reduce the sun exposure required for the body to synthesize vitamin D3. Supplementing with vitamin D3 has been linked to a number of health benefits: optimising muscle function and remodelling, maintaining bone health and minimizing infection risk.
One of the functions of training is to provide a stimulus to the working muscle, causing stress on the muscle and muscular damage. The process of repairing and remodelling the muscle results in beneficial adaptations and improved physical performance. It has been shown that supplementing with vitamin D3 has the potential to influence muscle remodelling (3). Additionally, it has been suggested that vitamin D deficiency has a negative impact on muscular performance (4) and improved exercise performance has been seen alongside vitamin D3 supplementation (4, 5).
Vitamin D supports calcium absorption and utilisation with the body, meaning that vitamin D supplementation may have a role to play in bone health. Bone is an active tissue in the body and high-impact, loading type activities provide the stimulus to maintain bone health, promoting peak bone mineral density. However, athletes undertaking non-weight-bearing exercise, such as cycling, are at an increased risk of low bone mineral density and subsequent poor bone health, with proposed beneficial effects of vitamin D supplementation on bone density (6).
Vitamin D also plays an important role in the immune system, with the activation of some immune cells being regulated by circulating vitamin D levels (3). Exercise can increase the chances of illness and the prevalence of upper respiratory tract infections (URTI) is higher in overreached endurance athletes (7). In endurance trained populations, vitamin D deficiencies resulted in more episodes of upper respiratory tract infections and more URTI symptom days (8). Additionally, vitamin D3 supplementation has been shown to prevent decreases in IL-5 compared to a placebo trial (9). Given that IL-5 is a cell of the immune system which protects against viruses and bacterial infections, this finding supports the notion that vitamin D3 may play a role in immune function support.
Take Home Messages:
- Friedl, C., & Zitt, E. (2017). Vitamin D prohormone in the treatment of secondary hyperparathyroidism in patients with chronic kidney disease. International journal of nephrology and renovascular disease, 10, 109.
- Close, G. L., Leckey, J., Patterson, M., Bradley, W., Owens, D. J., Fraser, W. D., & Morton, J. P. (2013). The effects of vitamin D3 supplementation on serum total 25 [OH] D concentration and physical performance: a randomised dose–response study. Br J Sports Med, 47(11), 692-696.
- Owens, D. J., Allison, R., & Close, G. L. (2018). Vitamin D and the Athlete: Current Perspectives and New Challenges. Sports Medicine, 1-14.
- Close, G. L., Russell, J., Cobley, J. N., Owens, D. J., Wilson, G., Gregson, W., … & Morton, J. P. (2013). Assessment of vitamin D concentration in non-supplemented professional athletes and healthy adults during the winter months in the UK: implications for skeletal muscle function. Journal of sports sciences, 31(4), 344-353.
- Wyon, M. A., Koutedakis, Y., Wolman, R., Nevill, A. M., & Allen, N. (2014). The influence of winter vitamin D supplementation on muscle function and injury occurrence in elite ballet dancers: a controlled study. Journal of science and medicine in sport, 17(1), 8-12.
- Neal, S., Sykes, J., Rigby, M., & Hess, B. (2015). A review and clinical summary of Vitamin D in regard to bone health and athletic performance. The Physician and sportsmedicine, 43(2), 161-168.
- Hausswirth, C., Louis, J., Aubry, A., Bonnet, G., Duffield, R., & Le Muer, Y. (2014). Evidence of disturbed sleep patterns and increased illness in functionally overreached endurance athletes. Medicine and science in sports and exercise.
- He, C. S., Handzlik, M. K., Fraser, W. D., Muhamad, A. S., Preston, H., Richardson, A., & Gleeson, M. (2013). Influence of vitamin D status on respiratory infection incidence and immune function during 4 months of winter training in endurance sport athletes. Exerc Immunol Rev, 19, 86-101.
- Barker, T., Martins, T. B., Hill, H. R., Kjeldsberg, C. R., Henriksen, V. T., Dixon, B. M., … & Weaver, L. K. (2012). Different doses of supplemental vitamin D maintain interleukin-5 without altering skeletal muscle strength: a randomized, double-blind, placebo-controlled study in vitamin D sufficient adults. Nutrition & metabolism, 9(1), 16.