Vitamin D, Total Unit Converter

Vitamin D is a fat-soluble vitamin and hormone precursor essential for calcium absorption, bone health, and numerous other physiological processes.

The 25-hydroxyvitamin D test (also called 25(OH)D or calcidiol) measures the main circulating form of vitamin D in your blood. This is the most accurate way to assess your vitamin D status.

Vitamin D exists in two forms: D2 (ergocalciferol) from plant sources and D3 (cholecalciferol) from animal sources and skin synthesis. The total 25(OH)D level combines both forms.

Vitamin D is primarily made in the skin when exposed to sunlight (UVB radiation converts 7-dehydrocholesterol to vitamin D3). It can also be obtained from dietary sources such as fatty fish, fortified foods, and supplements. The liver converts vitamin D to 25(OH)D, which is then activated in the kidneys to the hormone 1,25-dihydroxyvitamin D.