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Hypervitaminosis A refers to the toxic effects of ingesting too much preformed vitamin A. 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 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 fully recover. High intake of provitamin carotenoids (such as beta carotene) from vegetables and fruits does not cause hypervitaminosis A, as conversion from carotenoids to the active form of vitamin A is regulated by the body to maintain an optimum level of the vitamin. Carotenoids themselves cannot produce toxicity. == Signs and symptoms == Symptoms may include:〔http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001390/〕 * Abnormal softening of the skull bone (craniotabes—infants and children) * Blurred vision * Bone pain or swelling * Bulging fontanelle (infants) * Changes in consciousness * Decreased appetite * Dizziness * Double vision (young children) * Drowsiness * Headache * 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) * Irritability * Liver damage * 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) * Premature epiphyseal closure * Skin peeling, itching * Spontaneous fracture〔 * Yellow discoloration of the skin (aurantiasis cutis) * Uremic pruritus * Vision changes * Vomiting * Death 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hypervitaminosis A」の詳細全文を読む スポンサード リンク
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