Over the last decade, there has been a surge in research into the health benefits of vitamin D. Concurrently, we’re learning about the importance of vitamin D for athletes and sports performance. So, what is the function of vitamin D in exercise performance, what are the recommended levels for athletes, and how do active sportspeople ensure they’re getting enough? 

How does vitamin D work? 

Vitamin D is a fat-soluble vitamin, meaning it’s stored in our fat. We don’t produce vitamin D in our bodies, so we must obtain this nutrient from various sources. First, our skin makes vitamin D when exposed to UV rays from the sun. These UV rays hit the membrane of our skin, converting cholesterol to vitamin D. Second, we can get Vitamin D from certain dietary foods, such as fatty fish, mushrooms, cheese, and eggs. 

Then, this manufactured vitamin D is transported to every cell in our body. It is essential in controlling metabolic pathways such as cell growth, protein production, and immune system strengthening. Specifically, regarding bones, Vitamin D increases the absorption of calcium from the gut and helps transport this calcium directly to your bones. Vitamin D is an essential muscle nutrient that maximises muscle contraction and helps muscles recover from intensive exercise. 

How does vitamin D help athletes? 

Vitamin D influences crucial bodily functions, including bone health, muscle repair, acute inflammation, and immunity—all of which are essential for overall health, optimal training, and sports performance. There is a crucial link between Vitamin D and exercise performance. 

Maintaining satisfactory bone health is crucial for athletes. Vitamin D deficiency is a risk factor for poor bone remodelling and stress fractures. A recent study on female Navy recruits found that those who took vitamin D supplements were 20% less likely to develop stress fractures than those who didn’t. 

Vitamin D deficiency also significantly affects muscle function. One study of Chinese adolescent athletes discovered that those with severe vitamin deficiency had reduced forearm strength compared to those with normal levels. Another study found that higher vitamin D levels in athletic females are associated with increased muscle power and jump height. 

Ultimately, vitamin D plays a crucial role in the immune system. A deficiency in vitamin D can lead to increased inflammation after intense exercise sessions. Moreover, we know that athletes with vitamin D deficiency are more likely to contract illnesses such as coughs and colds. Athletes who frequently experience injuries or illnesses should have their vitamin D levels checked and corrected if they are low. 

Recommended levels of vitamin D for athletes 

Generally, we define vitamin D status by measuring the levels of active vitamin D in the blood:

  • Deficiency is < 50 (Nmole/L) 
  • Insufficiency (low deficiency) is between 50 and 75
  • Normal is > 75

However, we must have levels above >75 to store vitamin D in muscle and fat. 

Typically, the recommended daily intake of vitamin D is 1,000 units. However, if your levels are low (<75), you require more than 1000 units. The Endocrine Society of Canada recommends 1500-2200 units per day. 

How to get vitamin D in athletes? 

foods for athletes containing high Vitamin D such as fish and eggs

There are three primary ways to obtain vitamin D, each with its advantages and disadvantages.  

Sunlight 

We know that 15 minutes in sunlight, wearing a bathing suit, provides 10,000-20,000 units of vitamin D for a person with light skin. However, the amount of vitamin D produced by the sun is influenced by various factors. These include the time of year (UV rays are more potent in Summer), sunscreen use, and overall pigmentation (darker-skinned individuals are at a disadvantage). Additionally, we need to strike a balance between the damage to the skin caused by sunlight and our desire to increase vitamin D intake.

Overall, spending about 15 minutes in the sun with arms and legs uncovered twice weekly is enough to boost vitamin D levels. 

Dietary intake

Some common foods naturally contain vitamin D, such as salmon, fatty fish, mushrooms, cheese and egg yolks. Other vitamin D-fortified foods are milk, orange juice, and cereal. However, only 50% of what we consume is absorbed by our gut. Therefore, although we recommend consuming foods rich in vitamin D, most people require additional vitamin D from other sources. Using tanning beds is also effective, although it is recommended to use them moderately to avoid excessive skin damage. 

Vitamin D supplements and athletes 

Vitamin D3 supplements are more effective at increasing blood levels of vitamin D than vitamin D2. Vitamin D3 is derived from animal products, while Vitamin D2 is suitable for vegans.  

Recent studies have found that a high dose once a week is more effective than daily administration. High weekly doses result in a rapid increase in levels, compared to a slower growth rate with daily dosing.

So, we recommend a weekly dose for effectiveness and convenience. Depending on your blood levels, the weekly Vitamin D3 dose varies from 20000 to 40000 units. The number of doses can also vary from 4 to 8 doses. Follow your doctor’s guidance on the exact dose for you. 

Other frequently asked questions about Vitamin D for athletes:

Who is at risk of vitamin D deficiency?

Some individuals are more susceptible to developing vitamin D deficiency. These groups include:

  • Older people
  • Dark-skinned
  • People who limit sun exposure for medical or religious reasons
  • People with fat-absorption problems (celiac and inflammatory bowel disease). 

What conditions are associated with vitamin D deficiency?

If you have severe vitamin D deficiency, you may develop bone softening called rickets in children and osteomalacia in adults. 

Can I overdose on vitamin D?

It’s unlikely, even if you take a superdose (30,000 units) daily for a few months. Another study found that 50000 units per day for five months produced no toxicity. So, you’ll unlikely overdose on vitamin D through diet, sunlight, or supplements. 

What is the difference between vitamin D2 and vitamin D3 supplements? 

Vitamin D3 is the natural form of vitamin D found in animal products and produced by sunlight. Vitamin D2 is derived from non-animal sources and is more suitable for vegans. However, Vitamin D2 is much less potent than Vitamin D3. So, although we can use vitamin D2 as a supplement, we prefer vitamin D3. 

What other factors are essential in maintaining bone health in athletes? 

Adequate calcium intake is also essential for bone health. Generally, we recommend consuming approximately 1,500 mg of calcium daily for optimal bone health. This means consuming at least four servings of calcium-rich foods daily, with each serving providing 400mg of calcium. A  calcium serving includes a small block of cheese, a glass of milk or a yoghurt tube. If you avoid dairy products, consider incorporating foods rich in calcium, such as eggs and fatty fish, into your diet. Some individuals may need to take calcium supplements to meet their daily calcium requirements. 

Additionally, consuming a sufficient number of calories is crucial for athletes to maintain healthy bones. Consistently low calorie intake can harm bone health and lead to reduced bone density and an increased risk of stress fractures. In women, irregular or absent periods could indicate chronic caloric deficiency. 

Does vitamin D deficiency increase the risk of stress fractures? 

We think so. Vitamin D deficiency can lead to brittle bones, thereby increasing the risk of stress fractures. Therefore, we recommend that anyone with a stress fracture be checked for vitamin D deficiency and the deficiency corrected if present. 

Final word from sportdoctorlondon about vitamin D and Exercise

Vitamin D is essential for many metabolic pathways in our body. Deficiency can lead to soft bone and stress fractures, although we know low levels have effects on other organs. If you have a vitamin D deficiency, you should increase your levels through exposure to sunlight, a balanced diet, and supplements. Weekly high doses are preferable to daily doses.  

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