Which vitamin is essential for vision and immune function?

Vitamin A is essential for vision and immune function due to its crucial role in the maintenance of healthy vision and the functioning of the immune system. Specifically, vitamin A is a key component of rhodopsin, a protein in the retina that allows the eyes to convert light into nerve signals, thereby enabling sight, particularly in low-light conditions.

Moreover, vitamin A is involved in the production and function of white blood cells, which are vital for the immune response. It contributes to the integrity of mucosal surfaces, enhancing the body's defense mechanisms against infections. This dual role is what makes vitamin A particularly significant to both vision and immunity.

Other vitamins mentioned do play roles in various body functions, such as vitamin C being important for skin health and antioxidant protection, vitamin D being crucial for calcium metabolism and bone health, and vitamin K being essential for blood clotting. However, none of these have the same direct relationship with vision as vitamin A does.