This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrine System, Subject name: Physiology
Secondary hyperparathyroidism due to Vit D deficiency shows: 
Select and explain. 
A. Hypocalcemia, B. Hypercalcemia, C. Hypophosphatemia, D. Hyperphosphatemia
C: Hypophosphatemia
Answer: C: Hypophosphatemia 
Explanation: Vitamin D deficiency causes hypocalcemia and hypomagnesemia and decreases GI absorption of calcium and phosphate. Decreased serum Ca2+ will stimulate PTH secretion. The secondary hyperparathyroidism will bring the Ca2+ levels toward normal but cause phosphaturia. Thus serum phosphate loss will be fuher aggravated - hypophosphatemia. The level of calcium phosphate product is low, bone mineralization is impaired and demineralization is increased.