Vitamin D is one of the most vital nutrients required by our bodies in order to function at our best. Synthesised by our skin from sunlight, it should be easily available, and yet Vitamin D deficiency is highly prevalent globally, causing issues from fatigue and muscle weakness to increased stress fractures. Adequate Vitamin D levels are especially important for runners as the high impact nature of the activity places a huge stress on the bones.
What is Vitamin D?
Vitamin D is not technically a vitamin but a prohormone – a substance that the body converts to a hormone. Unlike other vitamins, only a tenth of the Vitamin D required by the body comes from food with 90% being made by the body itself.
Vitamin D has two main forms: D2 and D3. You may have heard them used interchangeably but they are actually different in a few important ways.
- Derived from animal products such as oily fish, fish oil, egg yolk, liver
- Present in microalgae
- Produced in the skin in reaction to sunlight
- More effective at improving Vitamin D status than Vitamin D2
- Derived mainly from plant sources such as mushrooms and fortified foods
- Produced by plants and mushrooms in reaction to sunlight
- Not as effective as Vitamin D3 at improving Vitamin D status
- Vitamin D2 supplements are potentially more sensitive to humidity and temperature fluctuations, making them more likely to degrade over time
What are the natural sources of Vitamin D?
Vitamin D is naturally present in a few foods and added to others, but only about 10% of it comes from our diet. The main source of Vitamin D is sunshine; the skin reacts to the UVB radiation present in sunlight with an UV index of three or more, by synthesising Vitamin D3 (cholecalciferol). The stronger the sunlight, the more Vitamin D your skin will produce. This itself poses a problem as sunblock used in order to prevent sunburn will also block the rays required for the synthesis.
Food sources with Vitamin D include:
- Fortified cereals and juices
- Fatty fish like salmon or tuna
- Egg yolks
What does Vitamin D do?
Vitamin D is best known for its role in bone health; it is essential for calcium absorption and bone mineralisation. Sufficient Vitamin D levels ensure 30-40% of dietary calcium is absorbed, compared to the measly 10-15% when your Vitamin D levels are low.
A number of studies have also suggested that Vitamin D plays a role in preventing fractures by improving muscle strength; stronger muscles support bones and also mean you will be less likely to fall.
Vitamin D also plays an important role in:
- Keeping your immune system fighting fit
- Supporting brain and nervous system health
- Preventing mood disorders like depression
- Regulating insulin levels and supporting diabetes management
- Supporting lung function and cardiovascular health
Vitamin D deficiencies
National surveys show 1 in 5 people in the UK have low levels of Vitamin D. In addition, recent large observational data have suggested that ~40% of Europeans are vitamin D deficient, and 13% are severely deficient.
Low vitamin D status can negatively impact the health and training efficiency of athletes. Suboptimal vitamin D status may increase risks for stress fractures, acute illness, and contribute to poor muscle function.
Causes of vitamin D deficiency include:
- Sunscreen; We are all very aware of the dangers of excess sun exposure and the risk of skin cancer (as little as 60 seconds of UVA exposure to the sun can increase your risk of melanoma) and accordingly protect ourselves with sunscreen. However, this will also reduce the body’s ability to absorb the UVB rays from the sun and interfere with Vitamin D production.
- Lack of sunlight; Northern latitudes, and the usual UK weather, are not exactly famous for their reliably sunny days and the hours of sunlight in the winter are fleeting. In addition, lifestyle or work patterns might mean you are not getting enough rays on your skin to allow adequate Vitamin D synthesis.
- Skin type; Darker skin reduces the body’s ability to absorb the UVB radiation necessary for Vitamin D production.
- Being overweight; Obese individuals have been found to have lower vitamin D levels. It's thought that this may be caused by vitamin D accumulating in the body's fatty tissue.
Symptoms of Vitamin D deficiency
The symptoms of Vitamin D deficiency are subtle and can be easy to miss. Some of the most common symptoms include:
- Bone and back pain
- Muscle pain
- Regular sickness or infection
- Impaired wound healing
- Hair loss
- Low mood
Complications rising from Vitamin D deficiency
If your body is deficient in Vitamin D for an extended time, it may result in some fairly serious complications:
- Weaker bones leading to (stress) fractures
- Cardiovascular conditions
- Autoimmune problems
- Neurological diseases
Vitamin D Supplements
The NHS advises everyone to take Vitamin D during the autumn and winter to keep their bones and muscles healthy and to support their general health. However, considering the prevalent rates of Vitamin D deficiency, supplementation year-round might be a good idea.
The current daily NRV (Nutrient Reference Level) for Vitamin D in the UK is 5μg, however the recommended levels of Vitamin D in the UK is 10μg.
5μg is the minimum amount of Vitamin D that the general population, as defined by the EU authorities, requires in order to not develop rickets, while 10μg is a better level for improved general health.
RunStrong contains 10μg of Vegan Vitamin D3 from algae.
Heaney R. P. (2008). Vitamin D in health and disease. Clinical journal of the American Society of Nephrology : CJASN, 3(5), 1535–1541. https://doi.org/10.2215/CJN.01160308
Shuler, F. D., Wingate, M. K., Moore, G. H., & Giangarra, C. (2012). Sports health benefits of vitamin d. Sports health, 4(6), 496–501. https://doi.org/10.1177/1941738112461621
Aydın, C. G., Dinçel, Y. M., Arıkan, Y., Taş, S. K., & Deniz, S. (2019). The effects of indoor and outdoor sports participation and seasonal changes on vitamin D levels in athletes. SAGE open medicine, 7, 2050312119837480. https://doi.org/10.1177/2050312119837480
Laird, E., Ward, M., McSorley, E., Strain, J. J., & Wallace, J. (2010). Vitamin D and bone health: potential mechanisms. Nutrients, 2(7), 693–724. https://doi.org/10.3390/nu2070693
de la Puente Yagüe, M., Collado Yurrita, L., Ciudad Cabañas, M. J., & Cuadrado Cenzual, M. A. (2020). Role of Vitamin D in Athletes and Their Performance: Current Concepts and New Trends. Nutrients, 12(2), 579. https://doi.org/10.3390/nu12020579
Ogan, D., & Pritchett, K. (2013). Vitamin D and the athlete: risks, recommendations, and benefits. Nutrients, 5(6), 1856–1868. https://doi.org/10.3390/nu5061856
Larson-Meyer, D. E., & Willis, K. S. (2010). Vitamin D and athletes. Current sports medicine reports, 9(4), 220–226. https://doi.org/10.1249/JSR.0b013e3181e7dd45
von Känel, R., Müller-Hartmannsgruber, V., Kokinogenis, G., & Egloff, N. (2014). Vitamin D and central hypersensitivity in patients with chronic pain. Pain medicine (Malden, Mass.), 15(9), 1609–1618. https://doi.org/10.1111/pme.12454
e Silva, A. V., Lacativa, P. G., Russo, L. A., de Gregório, L. H., Pinheiro, R. A., & Marinheiro, L. P. (2013). Association of back pain with hypovitaminosis D in postmenopausal women with low bone mass. BMC musculoskeletal disorders, 14, 184. https://doi.org/10.1186/1471-2474-14-184
Halliday, T. M., Peterson, N. J., Thomas, J. J., Kleppinger, K., Hollis, B. W., & Larson-Meyer, D. E. (2011). Vitamin D status relative to diet, lifestyle, injury, and illness in college athletes. Medicine and science in sports and exercise, 43(2), 335–343. https://doi.org/10.1249/MSS.0b013e3181eb9d4d
Hamilton, B., Grantham, J., Racinais, S., & Chalabi, H. (2010). Vitamin D deficiency is endemic in Middle Eastern sportsmen. Public health nutrition, 13(10), 1528–1534. https://doi.org/10.1017/S136898000999320X
Heaney, R. P., & Holick, M. F. (2011). Why the IOM recommendations for vitamin D are deficient. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research, 26(3), 455–457. https://doi.org/10.1002/jbmr.328
Heller, J. E., Thomas, J. J., Hollis, B. W., & Larson-Meyer, D. E. (2015). Relation between vitamin D status and body composition in collegiate athletes. International journal of sport nutrition and exercise metabolism, 25(2), 128–135. https://doi.org/10.1123/ijsnem.2013-0250
Hossein-nezhad, A., & Holick, M. F. (2013). Vitamin D for health: a global perspective. Mayo Clinic proceedings, 88(7), 720–755. https://doi.org/10.1016/j.mayocp.2013.05.011
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 : the official journal of the American Society for Bone and Mineral Research, 23(5), 741–749. https://doi.org/10.1359/jbmr.080102
Willis, K. S., Smith, D. T., Broughton, K. S., & Larson-Meyer, D. E. (2012). Vitamin D status and biomarkers of inflammation in runners. Open access journal of sports medicine, 3, 35–42. https://doi.org/10.2147/OAJSM.S31022