Identifying Vitamin D's Active Form

Vitamin D is obtained from diet or synthesized in the skin and requires two hydroxylation steps to become biologically active.

• Step 1 (Liver): Vitamin D (Cholecalciferol or Ergocalciferol) is converted to 25-hydroxyvitamin D in the liver.
• Step 2 (Kidneys): 25-hydroxyvitamin D is further converted to the active form, 1,25-dihydroxyvitamin D, primarily in the kidneys.

This final form, 1,25-dihydroxyvitamin D (also known as Calcitriol), is the hormonally active form responsible for regulating calcium and phosphate levels.

While Cholecalciferol (Vitamin D3) and Ergocalciferol (Vitamin D2) are forms of Vitamin D, they are precursors. Dehydrocholesterol is a precursor to Vitamin D3 synthesis in the skin.

Therefore, the functionally active form is 1,25-Dihydroxycholecalciferol.