Winter is the prime time for infections to take hold, so supporting the immune system is essential. Making sure we take daily vitamin D3 is a proven way to help, meaning less time off sick and away from training. But how exactly does it work?

The key to better immune health

The human immune system includes a complex range of specialised immune cells, each with a role to play in fighting infections. In the 1980's, scientists discovered that these cells contain receptor sites for Vitamin D. If our immune cells are locked doors, Vitamin D is the key and scientists have been researching what this means for immunity ever since.

Vitamin D from the sun

The production of Vitamin D3 (which is technically a hormone) begins when cholesterol in our skin cells is exposed to the sun’s UVB rays. The resulting previtamin D3 (cholecalciferol) then travels to the liver, where it is converted to 25-hydroxyvitamin D (25(OH)D). This is the chemical that doctors usually measure to diagnose Vitamin D deficiencies. However, this Vitamin D will not achieve its active form until it reaches the kidneys where it becomes calcitriol. 

Reduced risk of colds and flu

For runners suffering from a cold, the general rule of the thumb is that you are ok to run as long as you don’t have a fever and your cold is limited above the neck. This means that if you develop a chesty cough or have any trouble breathing, running should definitely be off the agenda until you feel better. However, even a runny nose or a sore throat can be enough to zap your energy and make running miserable.

In 2017, a major meta-analysis (published in the British Medical Journal) pulled together 25 scientific trials. It found that Vitamin D supplementation was not only safe but also reduced the risk of people developing an upper respiratory tract infection (which includes colds, flu and pneumonia). This protective effect was stronger in people who didn’t have enough Vitamin D to begin with, emphasising the direct link of Vitamin D to better immunity.¹

Research such as this led to the UK government recommending Vitamin D supplementation, especially during autumn and winter. Similar research is building to determine the impact of Vitamin D supplements during our current pandemic, with experts suggesting the recommended dose should be increased to at least 800iu per day.²

Vitamin D deficiency is a global problem

Over 1 billion people worldwide, and at least 1 in 5 people in the UK, are estimated to be deficient in Vitamin D and this may be down to factors beyond the lack of sunlight hours (especially in winter).³  For example, the ability to produce Vitamin D3 becomes less effective as we age, meaning older people may need to supplement more. Those with pale skin prone to sunburn, those with dark skin and those who cover up or regularly use sunscreen may also need more.⁴  While most runners assume that due to the inevitably long hours spent outdoors, their Vitamin D levels would be sufficient, a 2008 study at the Cooper Clinic in Dallas found that 75% of runners averaging 20 miles a week have low Vitamin D levels.

Vitamin D is especially relevant for endurance runners

Strenuous exercise (such as endurance running) can temporary lower immune function, due to an increase in cortisol (the stress hormone) and muscular inflammation⁵, which can give infectious organisms a chance to take hold. In a study involving endurance runners, good Vitamin D levels were associated with less inflammation after a run.⁶ Vitamin D not only supports immunity, but also muscle function, stability, bone health and cognitive functions - all important for keeping runners on their feet. ^{7 8}

Reliable daily immune support

For immune support, it is important to make sure your daily supplement contains Vitamin D (especially in the form of D3 which is more effective than D2.⁹). This is why 400iu of vegan-sourced Vitamin D3 can be found in RunStrong, supporting a healthy immune system when it’s needed most.

References:

1. Martineau, A. R., Jolliffe, D. A., Hooper, R. L., Greenberg, L., Aloia, J. F., Bergman, P., Dubnov-Raz, G., Esposito, S., Ganmaa, D., Ginde, A. A., Goodall, E. C., Grant, C. C., Griffiths, C. J., Janssens, W., Laaksi, I., Manaseki-Holland, S., Mauger, D., Murdoch, D. R., Neale, R., Rees, J. R., … Camargo, C. A., Jr (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ (Clinical research ed.), 356, i6583. https://doi.org/10.1136/bmj.i6583

2. Griffin, G., Hewison, M., Hopkin, J., Kenny, R. A., Quinton, R., Rhodes, J., Subramanian, S., & Thickett, D. (2021). Preventing vitamin D deficiency during the COVID-19 pandemic: UK definitions of vitamin D sufficiency and recommended supplement dose are set too low. Clinical medicine (London, England), 21(1), e48–e51. https://doi.org/10.7861/clinmed.2020-0858

3. Holick, M. F., & Chen, T. C. (2008). Vitamin D deficiency: a worldwide problem with health consequences. The American journal of clinical nutrition, 87(4), 1080S–6S. https://doi.org/10.1093/ajcn/87.4.1080S

4. Davies, J. R., Chang, Y. M., Snowden, H., Chan, M., Leake, S., Karpavicius, B., Haynes, S., Kukalizch, K., Randerson-Moor, J., Elliott, F., Barth, J., Kanetsky, P. A., Harland, M., Bishop, D. T., Barrett, J. H., & Newton-Bishop, J. A. (2011). The determinants of serum vitamin D levels in participants in a melanoma case-control study living in a temperate climate. Cancer causes & control : CCC, 22(10), 1471–1482. https://doi.org/10.1007/s10552-011-9827-3

5. Nieman, D. C., & Wentz, L. M. (2019). The compelling link between physical activity and the body's defense system. Journal of sport and health science, 8(3), 201–217. https://doi.org/10.1016/j.jshs.2018.09.009

6. 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

7. Bischoff-Ferrari, H. A., Dawson-Hughes, B., Staehelin, H. B., Orav, J. E., Stuck, A. E., Theiler, R., Wong, J. B., Egli, A., Kiel, D. P., & Henschkowski, J. (2009). Fall prevention with supplemental and active forms of vitamin D: a meta-analysis of randomised controlled trials. BMJ (Clinical research ed.), 339, b3692. https://doi.org/10.1136/bmj.b3692

8. Beydoun, M. A., Hossain, S., Fanelli-Kuczmarski, M. T., Beydoun, H. A., Canas, J. A., Evans, M. K., & Zonderman, A. B. (2018). Vitamin D Status and Intakes and Their Association With Cognitive Trajectory in a Longitudinal Study of Urban Adults. The Journal of clinical endocrinology and metabolism, 103(4), 1654–1668. https://doi.org/10.1210/jc.2017-02462

9. Tripkovic, L., Lambert, H., Hart, K., Smith, C. P., Bucca, G., Penson, S., Chope, G., Hyppönen, E., Berry, J., Vieth, R., & Lanham-New, S. (2012). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. The American journal of clinical nutrition, 95(6), 1357–1364. https://doi.org/10.3945/ajcn.111.031070