Certified Nutrition Specialist (CNS) Practice Exam 2025 – All-in-One Guide to Master Your CNS Certification!

Vitamin D is essential for calcium absorption because it enhances the intestinal absorption of calcium from the diet. When calcium is consumed, it needs to be adequately absorbed through the intestinal walls, and vitamin D plays a pivotal role in this process.

It facilitates the synthesis of calcium-binding proteins in the intestinal mucosa, which are necessary for transporting calcium across the intestinal lining and into the bloodstream. Without sufficient vitamin D, the efficiency of calcium absorption is significantly reduced, leading to potential deficiencies and negative health outcomes such as weakened bones. Therefore, among the listed nutrients, vitamin D is the most critical for maximizing the body's ability to absorb calcium effectively.