Over the last decade, research into the health benefits of vitamin D has surged — and with it, our understanding of vitamin D in athletes and its role in sports performance. So what does vitamin D do in exercise? What are the recommended levels for athletes, and how do active people make sure they’re getting enough?
How does vitamin D work?
Vitamin D is a fat-soluble vitamin, stored in our body fat. We don’t make it from nothing — we get it two ways. First, our skin makes vitamin D when UV rays from the sun convert cholesterol in the skin. Second, we get it from certain foods, such as fatty fish, mushrooms, cheese, and eggs.
Once made, vitamin D travels to every cell in the body, helping to regulate metabolic pathways such as cell growth, protein production, and immune function. Specifically for bones, it increases calcium absorption from the gut and helps move that calcium into bone. It’s also an essential muscle nutrient, helping muscles contract and recover from intense exercise.
How does vitamin D help athletes?
Vitamin D influences bone health, muscle repair, inflammation, and immunity — all central to training and performance. There’s a clear link between vitamin D and exercise performance.
Bone health. Vitamin D deficiency is a risk factor for poor bone remodelling and stress fractures. A study of female Navy recruits found that those taking vitamin D supplements were 20% less likely to develop a stress fracture than those who didn’t take them.
Muscle function. Deficiency affects the muscle, too. One study of adolescent athletes found that those with severe deficiency had reduced forearm strength, and another found that higher vitamin D levels in athletic women were linked to greater muscle power and jump height.
Immunity. Vitamin D supports the immune system. Deficiency can lead to increased inflammation after intense exercise, and athletes with deficiency are more prone to coughs and colds. Athletes with frequent injuries or illnesses should have their vitamin D checked and corrected if low.
Recommended vitamin D levels for athletes
We define vitamin D status by the level of active vitamin D in the blood:
- Deficiency: under 50 nmol/L
- Insufficiency: 50–75 nmol/L
- Normal: over 75 nmol/L
Levels need to be above 75 to store vitamin D in muscle and fat. The usual recommended daily intake is around 1,000 units, but if your level is low (under 75), you need more — the Endocrine Society recommends 1,500–2,200 units a day in that situation.
How to get enough vitamin D
There are three main sources, each with pros and cons.
Sunlight
About 15 minutes in the sun in a swimsuit gives a light-skinned person 10,000–20,000 units. But this depends on the time of year (UV is stronger in summer), sunscreen, and skin pigmentation (darker skin produces less melanin). You also have to balance UV skin damage against the vitamin D benefit. As a rule, around 15 minutes in the sun with arms and legs uncovered, twice a week, is enough to boost levels.
Diet
Foods naturally containing vitamin D include salmon and other fatty fish, mushrooms, cheese, and egg yolks; fortified foods include some milk, orange juice, and cereal. But we absorb only about half of what we eat, so while a vitamin D-rich diet helps, most people still need additional vitamin D from other sources.
Foods naturally containing vitamin D include salmon and other fatty fish, mushrooms, cheese, and egg yolks; fortified foods include some milk, orange juice, and cereal. But we absorb only about half of what we eat, so while a vitamin D-rich diet helps, most people still need additional vitamin D from other sources.
Supplements
Vitamin D3 raises blood levels more effectively than D2 (D3 comes from animal products; D2 suits vegans). Recent studies suggest a high weekly dose works better than daily dosing, raising levels faster. So we generally recommend a weekly dose for both effectiveness and convenience — a weekly D3 dose of 20,000–40,000 units, over 4–8 doses, depending on your blood level. Follow your doctor’s guidance on the exact dose.
Frequently asked questions about vitamin D for athletes
Does vitamin D deficiency increase the risk of stress fractures?
We think so. Deficiency can lead to weaker bones and a higher risk of stress fractures, which is why we recommend that anyone with a stress fracture be checked for vitamin D deficiency and corrected if low.
Who is at risk of vitamin D deficiency?
Older people, those with darker skin, people who limit sun exposure for medical or religious reasons, and people with fat-absorption problems such as coeliac or inflammatory bowel disease.
Can I overdose on vitamin D?
It’s unlikely. Even large doses over months have shown little toxicity in studies — you’re very unlikely to overdose through diet, sunlight, or sensible supplementation. Still, take supplements as advised rather than in an open-ended way.
What’s the difference between vitamin D2 and D3?
D3 is the natural form found in animal products and made by sunlight; D2 comes from non-animal sources and suits vegans. D2 is considerably less potent, so we generally prefer D3.
What else matters for bone health in athletes?
Adequate calcium — around 1,500 mg a day (about four servings of calcium-rich food, each ~400 mg, such as a glass of milk, a small block of cheese, or a yoghurt). And enough calories: persistently low energy intake harms bone density and raises stress-fracture risk. In women, irregular or absent periods can signal chronic energy deficiency and warrant assessment.
Does vitamin D actually improve athletic performance?
Correcting a deficiency supports muscle strength, power, and recovery, and reduces injury and illness — so a deficient athlete who corrects their levels may perform better. There’s less evidence that extra vitamin D helps an athlete with normal levels, so the aim is to reach and maintain a healthy level, not to megadose.
Final word from Sport Doctor London about vitamin D and exercise
Vitamin D is essential for many pathways in the body. Deficiency can lead to soft bones and stress fractures, and affect muscle and immunity too. If you’re deficient, raise your levels through sunlight, a balanced diet, and supplements — with weekly high doses generally preferable to daily ones. The goal is a healthy, maintained level rather than the highest possible one.
If you’re an athlete with recurrent injuries, stress fractures, or suspected vitamin D deficiency, Dr Masci can assess you in London and arrange the right tests. Contact the team here or call +44 (0) 203 488 0350.
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