(also see Beta-Carotene )

Vitamin A is essential for the maintenance of healthy epithelial tissue, which is found in the eyes, skin, respiratory system, GI and urinary tracts.

Vitamin A is an essential nutrient required for normal and night vision, maintaining healthy skin, and keeping mucous membranes moist and functioning. Vitamin A is also needed by the thymus gland and the bones.

Article: http://www.umm.edu/ency/article/002400.htm