Which vitamin is crucial for vision and immune function?

Vitamin A is essential for both vision and immune function. It plays a critical role in the formation of rhodopsin, a protein in the eyes that allows the retina to respond to light, making it vital for good vision, especially in low-light conditions. Additionally, Vitamin A is important for maintaining the health of the mucous membranes and the skin, which are the body's first line of defense against infections. This vitamin helps to support the immune system by promoting the development of white blood cells and enhancing their function, thereby helping to fight off pathogens.

While other vitamins mentioned in the options have various important functions—including some related to skin health and antioxidant activity—they do not specifically fulfill the critical roles that Vitamin A does in vision and immune response.