GLOSSARY

Vitamin D Status describes vitamin adequacy in the body, interpreted through laboratory markers, risk factors and individual context.

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.

Oily fish and fortified foods can provide vitamin D; UV-exposed mushrooms commonly supply D2 and many animal sources D3. Some supplemental D3 comes from lichen, so chemical name alone does not establish vegan origin. Skin production varies with season, clothing, environment and individual features; a universal sunlight exposure duration cannot be inferred for everyone.

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.

Intake, absorption and body status describe different stages. An apparently adequate recorded intake may coexist with malabsorption, illness or drug interactions. Conversely, one low-intake day does not establish clinical deficiency. Several days of intake, relevant history and an appropriate marker provide more information than one meal or nonspecific tiredness alone.

No single assay perfectly describes storage and function for every vitamin. Appropriate markers differ, and sampling time, inflammation, kidney function or recent supplementation can affect some results. Laboratory references are not automatically sports-performance targets. Interpretation therefore requires understanding the marker and clinical setting rather than comparing a result with an isolated online number.

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.