Hypervitaminosis A refers to the toxic effects of ingesting too much preformed vitamin A (retinyl esters, retinol, and retinal). Symptoms arise as a result of altered bone metabolism and altered metabolism of other fat-soluble vitamins. Hypervitaminosis A is believed to have occurred in early humans, and the problem has persisted throughout human history. Toxicity results from ingesting too much preformed vitamin A from foods (such as fish liver or animal liver), supplements, or prescription medications and can be prevented by ingesting no more than the recommended daily amount. Diagnosis can be difficult, as serum retinol is not sensitive to toxic levels of vitamin A, but there are effective tests available. Hypervitaminosis A is usually treated by stopping intake of the offending food(s), supplement(s), or medication. Most people make a full recovery. High intake of provitamin carotenoids (such as beta-carotene) from vegetables and fruits does not cause hypervitaminosis A. Signs and symptoms Symptoms may include: Changes in consciousness Decreased appetite Dizziness Vision changes, double vision (young children) Drowsiness Headache Irritability Nausea Poor weight gain (infants and children) Skin and hair changes Cracking at corners of the mouth Hair loss Higher sensitivity to sunlight Oily skin and hair (seborrhea) Skin peeling, itching Vomiting Yellow discoloration of the skin (aurantiasis cutis) Signs Abnormal softening of the skull bone (craniotabes—infants and children) Blurred vision Bone pain or swelling Bulging fontanelle (infants) Gastric mucosal calcinosis Heart valve calcification Hypercalcemia Increased intracranial pressure manifesting as cerebral edema, papilledema, and headache (may be referred to as Idiopathic intracranial hypertension) Liver damage Premature epiphyseal closure Spontaneous fracture Uremic pruritus Causes Hypervitaminosis A results from excessive intake of preformed vitamin A. Genetic variations in tolerance to vitamin A intake may occur, so the toxic dose will not be the same for everyone. Children are particularly sensitive to vitamin A, with daily intakes of 1500 IU/kg body weight reportedly leading to toxicity. Types of vitamin A It is "largely impossible" for provitamin carotenoids, such as beta-carotene, to cause toxicity, as their conversion to retinol is highly regulated. No vitamin A toxicity has ever been reported from ingestion of excessive amounts. Overconsumption of beta-carotene can only cause carotenosis, a harmless and reversible cosmetic condition in which the skin turns orange. Preformed vitamin A absorption and storage in the liver occur very efficiently until a pathologic condition develops. When ingested, 70–90% of preformed vitamin A is absorbed and used. Sources of toxicity