Can Vitamin D 25-OH help with Sport?

A 25-OH Vitamin D blood test can be helpful for sports performance, but the evidence is nuanced. Vitamin D is essential for muscle function, bone health, and immune regulation. Observational studies consistently show that athletes with low vitamin D levels (e.g., <20 ng/mL) tend to have reduced muscle strength, power, and endurance. However, randomized controlled trials (RCTs) in already-sufficient athletes often fail to show performance gains from supplementation. The strongest benefit appears in individuals who are deficient or insufficient. Testing 25-OH is therefore a reasonable first step to identify deficiency, especially for indoor athletes, those in northern latitudes, or with darker skin. If levels are low (<30 ng/mL), supplementation (typically 1000–4000 IU/day) may modestly improve outcomes like sprint speed, jump height, and recovery. For those with adequate levels, extra vitamin D does not enhance performance. Evidence is rated 'human-moderate' because while the biological mechanism is plausible, RCT results are mixed. Sources: PMIDs 25692883, 28232696, 30332617. Note: MyBody-X does not offer a vitamin D blood test; you need a clinical lab.