Which vitamin is essential for intestinal calcium absorption?

• A. Vitamin A
• B. Vitamin D
• C. Vitamin C
• D. Vitamin E

Answer: (B)

Vitamin D enables the gut to absorb calcium efficiently. Its active form, calcitriol, acts on intestinal cells to increase the production of calcium-binding proteins and transport channels, so calcium moves more readily from the lumen into the blood. This active, vitamin D–dependent transport is especially important when dietary calcium is limited. Without enough vitamin D, calcium absorption drops, which can lead to conditions like rickets in children and osteomalacia in adults. The other vitamins listed (A, C, and E) don’t regulate intestinal calcium absorption; they have other roles such as vision and epithelial health (A), collagen synthesis and antioxidant support (C), and antioxidant protection (E).