In a patient with celiac disease, what is a common cause of hypocalcemia?

• A. Pseudohypoparathyroidism
• B. Hyperparathyroidism due to bone resorption
• C. Osteomalacia due to decreased Vitamin D absorption with secondary hyperparathyroidism and low phosphorus
• D. Vitamin B12 deficiency

Answer: (C)

In celiac disease, fat-malabsorption reduces the absorption of fat-soluble vitamins, especially vitamin D. Vitamin D is essential for bringing calcium into the gut and for bone mineralization. When vitamin D deficiency develops, calcium absorption falls, leading to hypocalcemia. In response, the parathyroid glands raise PTH, causing secondary hyperparathyroidism. Over time this deficiency also leads to osteomalacia, the defective mineralization of bone, and PTH-driven phosphate wasting results in low phosphorus. This combination—osteomalacia from vitamin D malabsorption with secondary hyperparathyroidism and low phosphorus—best explains common hypocalcemia in this setting. The other options don’t fit: pseudohypoparathyroidism involves resistance to PTH, hyperparathyroidism from bone resorption would raise calcium, and vitamin B12 deficiency does not cause hypocalcemia.