Cholecalciferol In Extra Virgin Olive Oil Dietary SupplementSupports: Calcium and Bone Metabolism Immune FunctionJarrow Formulas Vitamin D3 provides cholecalciferol, the most bioavailable form of vitamin D. Vitamin D3 is converted by the kidneys into the hormone calcitriol, the active form of vitamin D3. Vitamin D3 enhances calcium and phosphorous absorption, stimulates the synthesis of osteocalcin (an important structural protein in bone), and supports a healthy immune response.