GLOSSARY

Cholecalciferol is the skin-produced form of vitamin D; its separate chemical name does not denote an additional nutrient or a different effect.

Dietary or skin-derived vitamin D undergoes conversion for its major actions. The liver mainly produces calcidiol and the kidney mainly calcitriol, with local conversion in some other tissues. These forms are not medicines or supplements to swap independently. The pathway distinguishes intake form, status marker and active hormone when reading a label or laboratory report.

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.

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.