Vitamin D3 Unit Converter

Vitamin D3 (cholecalciferol) is the form of vitamin D produced in your skin when exposed to sunlight and the form found in animal-based foods and most supplements.

After synthesis or ingestion, vitamin D3 is converted in the liver to 25-hydroxyvitamin D3 (calcifediol), the main circulating form measured in blood tests. This is then converted in the kidneys to the active hormone 1,25-dihydroxyvitamin D (calcitriol).

Vitamin D3 is more effective than vitamin D2 (ergocalciferol, the plant-derived form) at raising and maintaining blood levels. When testing shows fractionated results, D3 reflects sun exposure and animal-source intake, while D2 comes entirely from plant foods or supplements.

Vitamin D3 is synthesized in the skin through UV-B radiation converting 7-dehydrocholesterol to cholecalciferol. Dietary sources include fatty fish (salmon, mackerel, trout), fish liver oils, egg yolks, beef liver, and fortified foods such as milk and cereals.