Vitamin D is a fat-soluble vitamin that plays an important role in bone health within the human body. In the athletic population, Vitamin D has become a popular micronutrient in support of performance. Where do we get it from? The diet accounts for exogenously sourced Vitamin D, from natural foods, such as oily fish and egg yolks. However, known better as the sunshine vitamin, vitamin D is produced endogenously by ultraviolet B (UVB) rays (AIS, 2011).
Recommended Daily Allowance
Despite diet variations between countries, the recommended daily allowance (RDA) is 600IU (15 μg) for 1-70 year olds and 800IU (20 μg) for over 70 year olds (Institute of medicine, 2011). Dietary vitamin D intake only accounts for just a small amount of what the body requires due to the limited availability and therefore the principal source comes from sunlight exposure. Although depending on where you live in the world this may cause a reduced availability and potential deficiencies.
Vitamin D for the general population
Vitamin D deficiencies are more prevalent in those countries that are either situated >35° north and south of the equator, which have a restricted sunlight exposure and seasonal variation, and/or those countries and cultures with a low dietary availability (Willis et al., 2008). Some nations such as Canada and Scandinavia have already taken steps by vitamin D food fortification, whereas this remains a question for public health in continents such as Europe.
A systematic review of the efficacy of vitamin D food fortification by Black et al., (2012) reported an inadequate Vitamin D concentration in 70-75% of 19-64 year olds, during the winter months of January to March, demonstrating the impact of seasonal variability. Further analysis of the research, identified that food fortification could prevent these seasonal vitamin D deficiencies. Although food fortification would need to be country dependant as food stables vary by country. For example, milk which is often fortified is scarcely consumed in countries, such as India and Jordan. This study is one of many that has addressed the use of widespread supplementation as an alternative means of increasing vitamin D status, however it has often been reported that adherence to supplementation is low and therefore deemed as an unreliable strategy.
Too much of a good thing
A potential risk to a widespread food fortification and supplementation is the link to potential harm from high levels of serum concentrations. However, research has concluded that there was no associated harm from intakes of 10,000 IU/day (250 nmol/L) from vitamin D3. The current recommended dietary intake (RDI) however, is 600 IU/d, with an upper tolerable intake of 4000 IU/d (Institute of medicine, 2011). Therefore, increasing the current RDI would be well supported.
From the research it is easy to conclude that in some countries, particularly those with a restricted sunlight, that the general population suffer with vitamin D insufficiency which could compromise bone and overall health. Food fortification is therefore a sensible, efficacious and safe option. In support of this, Finland and the US have both implemented food fortification as a successful measure in raising vitamin D status. As for the use of supplementation, more research is required to determine positive adherence and to establish any possible long term adverse effects.
Vitamin D for Athletes
To date food fortification has been unsuccessful to fully compensate vitamin D insufficiencies, often due to dietary patterns, but insufficiencies appear to be heightened in certain ethnic and racial groups. Could this issue extend into the athletic population? For athletes, vitamin D status is more than a bone health issue, as vitamin D has potential performance benefits that should be explored.
Where bone health for athletes is less of a concern, stress fractures are real issue and the incidence of such injures have been reduced with vitamin D and calcium supplementation. A similar reduction was reported in female naval recruits, post vitamin D supplementation (Lappe et al., 2007). Justification for vitamin D supplementation in athletes has been demonstrated in other performance related areas too: the control of exercise induced inflammation (Muller et al., 1991); improving immunity, in particular reducing the incidence of influenza and the common cold (Aloia & Li-Ng, 2007) and the potential to improve muscle function and performance (Hamilton, 2009; Cannell et al., 2009).
Despite the additional performance potential there is no agreement that an athlete’s vitamin D recommendations should differ from the general population (Willis et al., 2008). There may however be additional risks to athletes, for example, those that have limited sunlight exposure, due to training indoors or those with high or low body fat.
Until we fully understand the benefits of vitamin D supplementation in the athletic population and the possible adverse affects of prolonged use, a sensible approach should be the adopted method. Athletes should be encouraged to do the following; a) have a rich dietary sources of vitamin D, b) those in higher latitudes should supplement with D3 during the winter months c) any supplementation should take into account baseline levels.
In conclusion, based on the evidence, a tailored food fortification plan should be adopted for ‘at risk’ countries to reduce the incidence of vitamin D insufficiency. For the athletic population, supplementation of up to 4000 IU/day for ‘at risk’ athletes should be promoted. For those athletes with a recognised deficiency, serum 25(OH)D concentration needs to be monitored before consuming above the upper tolerable intake.
When it comes to supplementation always read the labels and check the quality of your supplements, if in doubt, seek advice before consumption. At Platform Nutrition we would also advocate that any supplement you consume should be tested and registered with Informed-Sport.
Aloia, J., & Li-Ng, M. (2007). Re: epidemic influenza and vitamin D. Epidemiology And Infection, 135(7), 1095-1096.
Black, L., Seamans, K., Cashman, K., & Kiely, M. (2012). An Updated Systematic Review and Meta-Analysis of the Efficacy of Vitamin D Food Fortification. Journal Of Nutrition, 142(6), 1102-1108. doi:10.3945/jn.112.158014
Cannell, J. J., Hollis, B. W., Sorensen, M. B., Taft, T. N., & Anderson, J. J. (2009). Athletic Performance and Vitamin D. Medicine and Science in Sports and Exercise. doi:10.1249/MSS.0b013e3181930c2b
Hamilton, B. (2009). Vitamin D and Human Skeletal Muscle. Scandinavian Journal Of Medicine & Science In Sports, 20, 182-190. doi:10.1111/j.1600-0838.2009.01016.x
Lappe, J., Cullen, D., Haynatzki, G., Recker, R., Ahlf, R., & Thompson, K. (2008). Calcium and Vitamin D Supplementation Decreases Incidence of Stress Fractures in Female Navy Recruits. Journal Of Bone And Mineral Research, 23(5), 741-749. doi:10.1359/jbmr.080102
Muller, K., Diamant, M., & Bendtzen, K. (1991). Inhibition of production and function of interleukin-6 by 1,25-dihydroxyvitamin D3. Immunology Letters, 28(2), 115-120.
Ods.od.nih.gov,. (2014). Vitamin D — Health Professional Fact Sheet. Retrieved 26 September 2014, from http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
Ross, A. (2011). Dietary reference intakes (1st ed.). Institute of Medicine. Washington, DC: National Academies Press.
Vitamin D. (2011) (1st ed., pp. 1-2). Australian Institute of Sport. Retrieved from http://www.ausport.gov.au/ais/nutrition/supplements
Willis, K., Peterson, N., & Larson-Meyer, E. (2008). Should we be concerned about the vitamin D status of athletes?. Int J Sport Nutr Exerc Metab, 18(2), 204-224.