Continued deficiency leads to damage to eye tissue and irreversible blindness. Typically, the first symptom of vitamin A deficiency is night blindness (nyctalopia), which usually becomes apparent when the patients enter a dark place or is caught in the glare so oncoming headlights while driving at night.
Another sign affecting the eyes is xerophthalmia, which is characterized by dryness of the eye (because of inadequate mucus production), associated with the disappearance of goblet cells in the conjunctivas and the enlargement and keratinization of epithelial cells.
The US recommended Daily Allowance (RDA) of vitamin A for adults is 5000 IU (1000 retinol equivalents). Rich dietary sources of retinol (preformed vitamin A) include dairy products, eggs and organ meats.
Some carotenoids (found in deep-yellow and dark green vegetables) can be converted to vitamin A during digestion.
In the US diet, approximately half of the vitamin A activity is derived from B-carotene and other carotenoids. Vitamin A deficiency usually results from inadequate intake of foods high in vitamin A (liver, kidney, butter , milk, cream, cheese and fortified margarine) or carotene a precursor of vitamin A found in a dark green leafy vegetables and yellow or orange fruits and vegetables.
What are the symptoms of vitamin A deficiency?
