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Hypervitaminoses A and D
Hypervitaminosis A is excessive accumulation of vitamin A; hypervitaminosis D, of vitamin D. Although these are toxic conditions, they usually respond well to treatment. They’re most prevalent in infants and children, usually as a result of accidental or misguided overdosage by parents. A related, benign condition called hypercarotenemia results from excessive consumption of carotene, a chemical precursor of vitamin A.
Causes
Vitamins A and D are fat-soluble vitamins that accumulate in the body because they aren’t dissolved and excreted in the urine. (See Important facts about vitamins A and D.) In most cases, hypervitaminoses A and D result from ingestion of excessive amounts of supplemental vitamin preparations. A single dose of more than 1 million units of vitamin A can cause acute toxicity; daily doses of 15,000 to 25,000 units taken over weeks or months have proven toxic in infants and children. For the same dose to produce toxicity in adults, ingestion over years is necessary. Chronic ingestion of only 1,600 to 2,000 IU daily of vitamin D is sufficient to cause toxicity.
Hypervitaminosis A may occur in patients receiving pharmacologic doses of vitamin A for dermatologic disorders. Hypervitaminosis D may occur in patients receiving high doses of the vitamin as treatment for hypoparathyroidism, rickets, and the osteodystrophy of chronic renal failure, and in infants who consume fortified milk and cereals plus a vitamin supplement. Concentrations of vitamin A in common foods are generally too low to pose a danger of excessive intake. However, a benign condition called < /span>hypercarotenemia results from excessive consumption of vegetables high in carotene (a protovitamin that the body converts into vitamin A), such as carrots, sweet potatoes, and dark green, leafy vegetables.
Signs and symptoms
Chronic hypervitaminosis A produces anorexia, irritability, headache, hair loss, malaise, itching, vertigo, bone pain, bone fragility, and dry, peeling skin. It may also cause hepatosplenomegaly and emotional lability. Acute toxicity may also produce transient hydrocephalus and vomiting. (Hypercarotenemia produces yellow or orange skin coloration.)
Hypervitaminosis D causes anorexia, headache, nausea, vomiting, weight loss, polyuria, and polydipsia. Because vitamin D promotes calcium absorption, severe toxicity can lead to hypercalcemia, including calcification of soft tissues, as in the heart, aorta, and renal tubules. Lethargy, confusion, and coma may accompany severe hypercalcemia.
Diagnosis
A thorough patient history suggests hypervitaminosis A.
Patient history and an elevated serum calcium level (over 10.5 mcg/dl) suggest hypervitaminosis D.
In children, X-rays showing calcification of tendons, ligaments, and subperiosteal tissues support this diagnosis.
Withholding vitamin supplements usually corrects hypervitaminosis A quickly and hypervitaminosis D gradually. Hypercalcemia may persist for weeks or months after the patient stops taking vitamin D. Treatment for severe hypervitaminosis D may include glucocorticoids to control hypercalcemia and prevent renal damage. In the acute stage, diuretics or other emergency measures for severe hypercalcemia may be necessary. Hypercarotenemia responds well to a diet free of high-carotene foods.
❑ Keep the patient comfortable, and reassure him that symptoms will subside after he stops taking the vitamin.
❑ Make sure the patient or the parents of a child with these conditions understand that vitamins aren’t innocuous. Explain the hazards associated with excessive vitamin intake. Point out that vitamin A and D requirements can easily be met with a diet containing dark green, leafy vegetables; fruits; and fortified milk or milk products.
❑ To prevent hypervitaminosis A or D, monitor serum vitamin A levels in patients receiving doses above the recommended daily allowance and serum calcium levels in patients receiving pharmacologic doses of vitamin D.
Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Professional Guide to Diseases (Eighth Edition)
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2005
ISBN: 1-58255-370-X
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