What is the primary function of Vitamin A?

The primary function of Vitamin A is closely associated with vision and immune function. This vitamin plays a crucial role in the formation of rhodopsin, a pigment found in the retina that is essential for low-light and color vision. Additionally, Vitamin A supports the health and integrity of epithelial tissues, which includes the skin and the lining of various organs, thereby influencing immune function by helping the body defend against infections.

Furthermore, Vitamin A is vital for the regulation of gene expression, particularly in the development and functioning of white blood cells, which are integral to the immune system's ability to respond to pathogens. Its contribution to maintaining mucosal surfaces also plays a role in protecting against bacterial and viral infections.

Given these critical functions, Vitamin A is recognized as essential for both vision and immune competence, making this choice the most accurate answer to the question regarding its primary function.