Inadequate dietary intake of vitamin A — either preformed vitamin A molecules or provitamin A molecules, like beta-carotene — is the primary cause of vitamin A deficiency.[1][2][3] Common signs and symptoms of Vitamin A deficiency include damage to the skin, vision problems under dim light conditions (night blindness), and poor immune system function.[1][2][4] Vitamin A deficiency during pregnancy can also cause birth defects in babies and growth impairments in children.[1][3][4]
In developing countries, vitamin A deficiency increases the risk of respiratory infections and diarrhea and increases the risk of dying from such conditions.[1][2] Vitamin A deficiency also leads to xerophthalmia — a condition that damages the eyes and is the leading cause of blindness in developing countries.[5][1][4]
This variety of outcomes caused by vitamin A deficiency arises because the many forms of vitamin A have diverse functions in the body.[1][2]