Vitamin D: why it’s important for athletes and when you should take it

What is vitamin D?

Following exposure to the sun, particularly UVB rays, the dermis layer of the skin begins to make vitamin D_, specifically, vitamin D₃. While you can get vitamin D₃ from your diet, the quantities are much lower than those made in the skin. Once made or obtained from the diet, vitamin D₃ is converted into a pre-hormone called 25(OH)D – this is the main marker of vitamin D status and what is looked for in blood tests.

What does vitamin D do?

Vitamin D is mostly recognised for its role in calcium regulation and has been linked to bone health, with supplementation being used to reverse the bone disorder rickets. However, scientists over the last decade have found that many of the tissues in the human body are responsive to vitamin D. Research has since shown that vitamin D₃ may also improve muscle function, reduce infection risk and also improve cardiac health – all important factors for the triathlete.

With vitamin D₃ being made following exposure to the sun, several factors put athletes at risk of becoming deficient. These include the season, clothing, sun cream use, time spent indoors, and skin colour. Even if you train outside during the winter, additional long-sleeved layers reduce the amount of skin exposed to what little sun there may be. Also, the concentration of UVB radiation is not strong enough to stimulate sufficient production of vitamin D. When working with an athlete, I will typically recommend they supplement with vitamin D₃ between October and April, while advising them to train outside as much as possible.

How do you test your vitamin-D levels?

However, before supplementing, it’s worth having your vitamin D levels checked, which you can do with a simple blood test either through your doctor, an online test kit, or a Sports Performance Testing Centre like we have at Race Faster.

This should be followed up with a re-test approximately 16 weeks later. Most tests will also include a range of vitamins and hormones along with vitamin D status, so it’s definitely worth getting tested as the information can also inform the rest of your performance diet

How can you increase your vitamin-D intake?

While you can obtain some vitamin D from the diet, from sources such as oily fish, eggs, fortified foods such as cereals, or shitake mushrooms, supplementing with vitamin D₃ is the best way to increase your levels. There are many options available on the market including tablets and mouth sprays or drops. Most athletes could supplement with 4,000 IU per day of vitamin D₃.

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Stephen Smith Performance nutritionist

About

Stephen Smith (PhD, SENr) is performance nutritionist for Red Bull Athlete Performance Centre in Salzburg and tutor at the Institute of Performance Nutrition. He believes in a food first, evidence-informed approach to maximising the health and performance of athletes. He's passionate about providing relevant, easy-to-understand educational support to turn the science into applicable nutrition practice that improves health and performance. He's also committed to developing quality sports science and nutrition research that informs practice and ultimately improves the performance of athletes.