Which vitamin is essential for calcium absorption and bone mineralization?

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

Answer: (A)

The key idea here is understanding which nutrient controls how well calcium is absorbed from the gut and how bone mineralization proceeds. Vitamin D does both because it is converted in the body to calcitriol, a hormone that increases intestinal absorption of calcium and phosphate and supports bone mineralization. Calcitriol upregulates calcium-binding proteins in the intestinal lining, making calcium uptake much more efficient, which is essential for forming and maintaining strong bones. It also works with parathyroid hormone to help regulate blood calcium levels, ensuring there’s enough calcium available for bone formation. Deficiency impairs calcium absorption and bone mineralization, leading to rickets in children and osteomalacia in adults. Vitamin D sources include sun exposure and foods like fatty fish and fortified products.

Other vitamins have important roles elsewhere—Vitamin C helps with collagen synthesis, Vitamin A influences growth and differentiation, and Vitamin K is involved in activating bone-related proteins—but they do not directly control the intestinal absorption of calcium or the mineralization process like vitamin D does.