nutritional disorders
Zinc Toxicity
Introduction
Zinc (Zn) is contained mainly in bones, teeth, hair, skin, liver, muscle, leukocytes, and testes. Zinc is a component of several hundred enzymes, including many nicotinamide adenine dinucleotide (NADH) dehydrogenases, RNA and DNA polymerases, and DNA transcription factors as well as alkaline phosphatase, superoxide dismutase, and carbonic anhydrase. (See also Overview of Minerals .) The recommended upper limit in adults for zinc intake is 40 mg/day; the upper limit is lower for younger people. Toxicity is rare. Ingesting doses of elemental zinc ranging from 100 to 150 mg/day for prolonged periods interferes withcoppermetabolism and causes low bloodcopperlevels, red blood cell microcytosis, neutropenia, and impaired immunity; higher doses should be given only for short periods of time and the patient followed closely. Ingesting larger amounts (200 to 800 mg/day), usually by consuming acidic food or drinking from a galvanized (zinc-coated) container, can cause anorexia, vomiting, and diarrhea. Chronic toxicity may result incopperdeficiency and may cause nerve damage. Metal fume fever, also called brass-founders’ ague or zinc shakes, is caused by inhaling industrialzinc oxidefumes; it results in fever, dyspnea, nausea, fatigue, myalgias, and a metallic taste in the mouth. Symptom onset is usually 4 to 12 hours after exposure. Symptoms usually resolve after 12 to 24 hours in a zinc-free environment. Diagnosisof zinc toxicity is usually based on the time course and a history of exposure. Treatmentof zinc toxicity consists of eliminating exposure to zinc; no antidotes are available. 