Which vitamin is essential for calcium absorption and bone mineralization?

• A. Vitamin C
• B. Vitamin K
• C. Vitamin D
• D. Vitamin B12

Answer: (C)

Vitamin D is essential for calcium absorption and bone mineralization. In the intestinal lining, the active form of vitamin D increases the production of calcium-binding proteins that actively transport calcium from the gut into the bloodstream, making calcium more readily absorbed. It also helps promote phosphate absorption, which pairs with calcium to form hydroxyapatite crystals—the mineral component of bone. With sufficient vitamin D, minerals are available where and when the bone needs them, supporting proper bone formation.

When vitamin D is lacking, calcium absorption drops, serum calcium can fall, and bone mineralization becomes inefficient, leading to conditions like rickets in children and osteomalacia in adults. Other vitamins influence bone health in different ways—vitamin C is key for collagen in the bone matrix, vitamin K helps activate proteins involved in bone formation, and vitamin B12 supports overall cell function—yet none promote calcium absorption and bone mineralization as directly as vitamin D.