Which nutrient plays a key role in calcium absorption and bone mineralization?

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

Answer: (C)

Vitamin D enables calcium absorption and bone mineralization. It increases the intestine’s ability to absorb calcium (and phosphate) by promoting the production of calcium-binding proteins in enterocytes, which helps calcium move from the gut into the bloodstream. With more calcium available in the blood, bone mineralization proceeds more effectively as calcium and phosphate are deposited into the bone matrix. Vitamin D also supports bone health by acting on bone cells to promote mineral deposition and by helping regulate calcium levels in cooperation with parathyroid hormone. When vitamin D is deficient, calcium absorption falls, serum calcium drops, and bones become weaker, leading to issues like rickets in children or osteomalacia in adults. Vitamin D can come from sun exposure, foods such as fatty fish and fortified products, and supplements.

Other nutrients have different roles. Vitamin C is important for collagen synthesis in the bone matrix, vitamin B12 supports red blood cell formation and nerve function, and iron is essential for oxygen transport and other metabolic processes; none directly regulate calcium absorption and bone mineralization as vitamin D does.