Verdict: Worth correcting if a blood test shows you are low, but there is no reliable evidence that vitamin D raises VO2max in people with normal levels.
Safety: Safe at usual doses; long-term high doses can raise blood calcium, so test levels and stay within medical advice
Key takeaways
A 2015 meta-analysis found 56% of athletes had inadequate vitamin D, with higher risk in winter, indoor sports and at higher latitudes
Randomised trials on VO2max disagree, from no effect in Gaelic footballers to a small gain in active men
Test your 25-hydroxyvitamin D level before supplementing and treat a deficiency rather than chasing a performance boost
Vitamin D is one of the most commonly taken supplements among athletes, and it is often marketed as a performance aid. The research tells a quieter story: vitamin D deficiency is common and worth fixing, but there is no consistent evidence that topping up raises VO2max in people who already have enough.
What it is
Vitamin D is a fat-soluble vitamin made in the skin when it is exposed to sunlight (UVB), with smaller amounts from oily fish, egg yolks and fortified foods. The liver converts it to 25-hydroxyvitamin D, the form measured in blood tests. Its best-known role is in calcium absorption and bone health, but vitamin D receptors are also found in skeletal muscle, which is why it attracts interest in sport.
Does it raise VO2max?
Randomised trials point in different directions:
- No effect: Todd and colleagues (2017) gave 42 Gaelic footballers 3,000 IU a day of vitamin D3 or placebo for 12 weeks. About 70% had insufficient or deficient levels at the start. Supplementation raised vitamin D levels but had no significant effect on VO2max, jump height, grip strength or lung function.
- Small benefit: Ramezani Ahmadi and colleagues (2020) gave 46 active men 2,000 IU a day or placebo for 12 weeks. The vitamin D group ended with higher VO2max and average Wingate power than the placebo group.
Small trials, different starting levels and different populations make it hard to draw a firm conclusion. The most plausible reading is that vitamin D may help aerobic capacity when it corrects a real deficiency, and does little otherwise. VO2max is set mainly by the heart and blood (see what limits VO2max), and vitamin D does not act directly on either.
Does it improve endurance performance?
Direct evidence on endurance performance is thin. The clearest pooled data concern strength: a meta-analysis by Zhang, Quan and Cao (2019) of eight trials in 284 athletes found that vitamin D supplementation improved lower-limb strength but not upper-limb strength or jumping power, with larger effects in athletes who trained indoors. That is relevant for runners and cyclists only indirectly — strong legs help economy and injury resistance (see strength training for runners) — but it is not proof of faster race times.
How it is used in studies
The trials above used vitamin D3 at 2,000–3,000 IU a day for 12 weeks, as capsules or oral sprays. The amount you need depends on your starting level, body size, skin type, season and sun exposure. That is why a blood test should come first, and why repeated testing is useful to make sure you end up in the normal range rather than far above it.
Side effects, safety and anti-doping
- At usual doses, vitamin D is well tolerated.
- Too much for too long can raise blood calcium (hypercalcaemia), causing nausea, vomiting, weakness, confusion and kidney problems. Toxicity almost always comes from high-dose supplements, not sunlight.
- Interactions and conditions: people with kidney disease, sarcoidosis, high calcium levels, or who take medications such as some diuretics or heart drugs should talk to a doctor before supplementing.
- Anti-doping: vitamin D is not prohibited, but supplements can be contaminated. If you compete, choose third-party tested products.
This page is not medical advice. Test before supplementing vitamin D and talk to a doctor if you have a medical condition or take medication.
Who might benefit
A meta-analysis by Farrokhyar and colleagues (2015) of 23 studies covering 2,313 athletes found that 56% had inadequate vitamin D, with the risk higher in winter and spring, in indoor sports and at higher latitudes. People more likely to be low include:
- Athletes training mostly indoors, or in the early morning and evening
- People living far from the equator, especially in winter
- People with darker skin living at higher latitudes
- Anyone who covers most of their skin outdoors or uses a lot of sunscreen
If you fall into one of these groups, ask for a 25-hydroxyvitamin D test. Fixing a deficiency is good for bones and general health whether or not it moves your VO2max.
Bottom line
Vitamin D is a "fix the gap" nutrient, not a performance enhancer. Inadequate levels are common in athletes and worth correcting after a blood test. Trials on VO2max are mixed, so don't expect a fitness boost from taking more than you need. Training is what raises VO2max — see how to improve VO2max and structured intervals. Compare other options on the supplements page, including iron, and track your progress with the VO2max calculator.
Frequently asked questions
Does vitamin D increase VO2max?
The evidence is mixed. One 12-week trial in active men found higher VO2max with 2,000 IU a day, while a similar trial in Gaelic footballers found no effect even though it corrected deficiency.
Does vitamin D improve athletic performance?
A meta-analysis of trials in athletes found a benefit for lower-limb strength but not for upper-limb strength or jumping power. Effects on endurance are not well established.
Should athletes test their vitamin D?
Yes, especially in winter, if they train indoors or live far from the equator. A blood test for 25-hydroxyvitamin D shows whether you need to supplement and by how much.
Can you take too much vitamin D?
Yes. Very high doses taken for a long time can raise blood calcium and cause nausea, weakness and kidney problems. Stick to medical advice and recheck levels.
Sources
- Farrokhyar F, Tabasinejad R, Dao D, et al. Prevalence of vitamin D inadequacy in athletes: a systematic-review and meta-analysis. Sports Med. 2015. PMID 25277808.
- Todd JJ, McSorley EM, Pourshahidi LK, et al. Vitamin D3 supplementation using an oral spray solution resolves deficiency but has no effect on VO2 max in Gaelic footballers: results from a randomised, double-blind, placebo-controlled trial. Eur J Nutr. 2017;56(4):1577–1587. doi:10.1007/s00394-016-1202-4
- Ramezani Ahmadi A, Mohammadshahi M, Alizadeh A, Ahmadi Angali K, Jahanshahi A. Effects of vitamin D3 supplementation for 12 weeks on serum levels of anabolic hormones, anaerobic power, and aerobic performance in active male subjects: a randomized, double-blind, placebo-controlled trial. Eur J Sport Sci. 2020. PMID 31957555.
- Zhang L, Quan M, Cao ZB. Effect of vitamin D supplementation on upper and lower limb muscle strength and muscle power in athletes: a meta-analysis. PLoS One. 2019. PMID 31039170.