Which vitamin has the function to absorb calcium?

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

Answer: (C)

Vitamin D controls calcium absorption in the gut. Its active form, calcitriol, stimulates the intestinal cells to produce calcium-binding proteins and transport systems, enabling calcium to be actively absorbed from the diet into the bloodstream. Without sufficient vitamin D, calcium absorption is impaired, which can lead to weaker bones and conditions like rickets in children or osteomalacia in adults. The other vitamins listed don’t drive the uptake of calcium in the intestines—A and E serve different roles (vision/gene expression and antioxidant protection), while K is mainly involved in blood clotting and bone protein modification, not calcium absorption.