Vitamin A is a fat-soluble vitamin derived from provitamin carotenoids and preformed retinoids. You can obtain retinoids from your diet by eating animal foods such as dairy products, eggs, kidney and liver. You can also get vitamin A by consuming foods rich in beta-carotene such as carrots and yellow or dark vegetables.
Physiological Functions
Vitamin A helps your eyes to adapt to light changes. According to Colorado State University Extension, it also plays a vital role in tooth development, immune system regulation, gene expression, cell division, bone growth and reproduction. In addition, vitamin A keeps your lungs, throat, nose, eyes, skin and mouth moisturized. If you have sufficient amounts of vitamin A, you may reduce your chances of developing some cancers. The recommended dietary allowance is 900 micrograms daily for men and 700 micrograms per day for women.
Deficiency Stages
The clinical manifestations of vitamin A deficiency occur in stages. In the early stage of deficiency, you will suffer from night blindness, and you may not be able to see properly in a dimly lit room. If the deficiency advances, you will not see anything in dim light. At this point, you should consult your physician, or else you may develop xerosis conjunctiva. Your conjunctiva, the lining under the eyelids that covers the white of the eye, will be pigmented, thickened, dry and wrinkled. At this stage, your eyeballs gain a misty appearance. Should the dryness spread further, your cornea will become hazy and lusterless. At that point, you are suffering from xerosis cornea, and you need to get medical attention or else you will develop keratomalacia, an ulceration of the cornea.