Evidence check: Vitamin D 25-OH in the context of Sport

Measuring 25-hydroxyvitamin D (25-OH vitamin D) in the context of sport is relevant because vitamin D is critical for bone health, muscle function, immune defense, and inflammation regulation. Deficiency can impair recovery, increase injury risk, and reduce performance. The evidence is nuanced: observational studies link low vitamin D levels with reduced muscle strength and higher infection rates. Randomized controlled trials (RCTs) show mixed results – in athletes with confirmed deficiency, supplementation improves outcomes like jump height or sprint time, while in replete individuals no additional performance benefit is seen. The MyBody-X test measures 25-OH vitamin D as a screening tool, but it has limitations: it is a single time-point measurement subject to seasonal variation and cannot determine causes or guide dosing. Self-interpretation without medical supervision is not recommended, as overdosing (hypercalcemia) carries risks. The evidence for the test itself is classified as 'practice' – it provides orientation, not diagnosis. For a sports medicine evaluation, additional factors such as training status, sun exposure, and individual genetics (e.g., VDR polymorphisms) should be considered. In summary, vitamin D testing is useful for at-risk groups (e.g., indoor athletes, winter season), but the evidence for performance enhancement in those with normal levels is weak.