Cholecalciferol is a form of Vitamin D, also called vitamin D3. 7-Dehydrocholesterol is the precursor of vitamin D3 and only forms the vitamin after being exposed to UV irradiation. After exposure to the sun, cholecalciferol is sent to the liver to be hydroxylated where it becomes 25-Hydroxyvitamin D3. Next, it is sent to the Kidney and once again hydroxlyated becoming 1,25-Hydroxyvitamin D3. 1,25-Hydroxyvitmain D3 is the active hormone form of vitamin D3.