nutritional disorders
Vitamin A Toxicity
Etiology ofVitamin AToxicity
Acutevitamin Atoxicityin children may result from taking large doses (>300,000 units [>100,000 RAE]), usually accidentally. In adults, acute toxicity has occurred when arctic explorers ingested polar bear or seal livers, which contain several million units ofvitamin A. Chronicvitamin Atoxicityin older children and adults usually develops after doses of>100,000 units (> 30,000 RAE)/day have been taken for months. Megavitamin therapy is a possible cause, as are massive daily doses (150,000 to 350,000 units [50,000 to 120,000 RAE]) ofvitamin Aor its metabolites, which are sometimes given for nodular acne or other skin disorders. Adults who consume>4500 units (> 1500 RAE)/day ofvitamin Amay develop osteoporosis. Infants who are given excessive doses (18,000 to 60,000 units [6,000 to 20,000 RAE]/day) of water-misciblevitamin Amay develop toxicity within a few weeks. Birth defects occur in children of women receivingisotretinoin(which is related tovitamin A) for acne treatment during pregnancy. Megadoses ofvitamin Acan cause liver toxicity. Although carotene is converted tovitamin Ain the body, excessive ingestion of carotene causes carotenemia, notvitamin Atoxicity. Carotenemia is usually asymptomatic but may lead to carotenosis, in which the skin becomes yellow. 