This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Medicine
Osteoporosis in steroid taking patients can be explained by all except 
Select and explain. 
A. decreased absorbtion of calcium from gut, B. increased excretion of calcium by kidney, C. decreased synthesis of vitamin D, D. increased demineralisation from bone
C: decreased synthesis of vitamin D
Answer: C: decreased synthesis of vitamin D 
Explanation: Ans c: (decreased .synthesis of vitamin D) Ref Goodwann& Gillmann chap 59Osteoporosis of glucocorticoid therapy is dose and duration dependent. Ribs and vertebrae are most common site of fracture.Mechanism:1. Inhibition of bone formation due to suppressive effect on osteoblast and stimulation of resorption due to effect on osteoclast mediated by changes in production of osteoprotegerin and RANK ligand2. decreased intestinal absorbtion of calcium-20 increase in parathormone-bone resorption3. increased excretion of calcium via kidney4. Inhibit gonadal steroid hormone