GLOSSARY

Vitamin D Deficiency is a state of inadequate vitamin supply for health or a low validated status marker under the relevant clinical criteria.

Bone pain or stress injury calls for broader assessment; vitamin status is considered with energy availability, training load and bone health.

Definitions of vitamin D adequacy and insufficiency differ between guidance and clinical settings. Observational associations do not establish a higher universal target for every athlete. Testing and repeat testing need a clear interpretation purpose. Deficiency and bone problems deserve assessment, but the vitamin's role alone does not justify more-is-better dosing or repeated tests for every healthy person.

Calcidiol or 25(OH)D is the usual vitamin D status marker; calcitriol is not routinely interchangeable for that purpose because hormonal regulation differs. Units matter: 1 nanogram per millilitre equals 2.5 nanomoles per litre. This is a unit conversion, not a diagnostic threshold or athlete target; the exact assay name must accompany the value.

Vitamin D supports calcium and phosphate regulation and bone mineralisation. Athletes' bone health also depends on energy availability, calcium, mechanical loading and hormonal conditions. Bone pain or stress injury should not be attributed only to D. Correcting deficiency may contribute, but cannot replace training-load management and an adequate overall diet.