Which form of Vitamin D is considered the most active?

• A. Cholecalciferol
• B. Calcidiol
• C. Calcitriol
• D. Ergocalciferol

Answer: (C)

Calcitriol is recognized as the most active form of Vitamin D in the body. It is the hormone form and is produced in the kidneys from calcidiol. Calcitriol plays a crucial role in regulating calcium and phosphate levels in the blood and is vital for maintaining bone health. It acts on various tissues, enhancing the intestinal absorption of calcium and phosphate, promoting mineralization of bone, and modulating parathyroid hormone secretion.

Understanding the roles of other forms of Vitamin D is also important. Cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2) are precursors that the body must convert into their active forms. Calcidiol, which is the result of the liver converting cholecalciferol, is less active than calcitriol. While all these forms are important in the overall metabolism of Vitamin D, it is calcitriol that directly exerts the biological effects necessary for calcium homeostasis and bone health.