Vitamin A is readily destroyed upon exposure to heat, light, or air. The vitamin, which functions directly in , is convert.... vitamin ey

Vitamin A is required by humans in very small amounts; the recommended intakes for adult men and women are 1,000 and 800 micrograms (?g; 1 ?g = 0.000001 gram), respectively, with an extra allowance for women who are pregnant or lactating. ( See .) Deficiency of vitamin A results in various disorders that most commonly involve the eye and the epithelial tissues. The mucous surfaces of the eye may become eroded in spots, allowing infection to set in, thus leading to ulceration and other destructive changes of the (the transparent outer covering of the eye) and other eye structures. Early signs of vitamin A deficiency may also be reflected in changes in the mucous membranes of the mouth, throat, and respiratory and genito-urinary passages. vitamin ey