Which of the following substances plays a critical role in collagen synthesis?

The role of Vitamin C in collagen synthesis is pivotal because it acts as a cofactor for the enzymes that are involved in the hydroxylation of proline and lysine residues in collagen. This hydroxylation is essential for the stabilization and structural integrity of collagen fibers, which are crucial for tissue strength and elasticity. Without adequate Vitamin C, collagen production can be hindered, leading to weakened connective tissues and conditions such as scurvy, characterized by symptoms like poor wound healing and skin abnormalities.

The other substances mentioned do not have a direct role in collagen synthesis. For instance, Vitamin D primarily aids in calcium absorption and is more involved in bone health rather than directly affecting collagen production. Vitamin B12 is essential for red blood cell formation and neurological function, but it does not directly influence collagen synthesis. Calcium, while important for bone density and overall cellular function, does not participate directly in the synthesis of collagen itself.