Which hormone increases the deposition of calcium into bones?

• A. Parathyroid Hormone
• B. Calcitonin
• C. Osteocalcin
• D. Vitamin D

Answer: (B)

Calcium homeostasis and bone remodeling are regulated by hormones that tilt the balance toward deposition in bone or release into the blood. Calcitonin lowers blood calcium by inhibiting osteoclasts, the cells that break down bone. With osteoclast activity reduced, calcium stays in the bone and is deposited into the bone matrix, making this hormone the one that promotes calcium deposition into bone.

Parathyroid hormone, in contrast, raises blood calcium by stimulating osteoclast-mediated bone resorption and by increasing renal calcium reabsorption and activation of vitamin D. Osteocalcin is a bone-derived protein linked to mineralization, but it isn’t the primary regulator that promotes calcium deposition in response to circulating calcium levels. Vitamin D supports calcium absorption from the gut and aids bone mineralization, but its main effect isn’t the direct deposition of calcium into bone like calcitonin’s.