Question

which is the biologically active hormone, sometimes called active vitamin d?
a. ergocalciferol
b. cholecalciferol
c calcitriol
d. calcidiol

Explanation:

To determine the biologically active form of vitamin D (also acting as a hormone), we analyze each option:

• Option a (Ergocalciferol): This is vitamin D₂, a dietary or supplemented form, not the active hormone.
• Option b (Cholecalciferol): This is vitamin D₃, synthesized in the skin or obtained from diet, but it is a precursor, not the active form.
• Option c (Calcitriol): Calcitriol (1,25 - dihydroxyvitamin D₃) is the biologically active hormone form of vitamin D. It functions in calcium and phosphorus homeostasis, acting on the intestines, bones, and kidneys.
• Option d (Calcidiol): This is 25 - hydroxyvitamin D, an intermediate metabolite in the activation pathway of vitamin D, not the active hormone.

Answer:

c. Calcitriol