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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. A diet high in fiber and phytate (eg, containing whole-grain bread) reduces zinc absorption.
Deficiency:
Dietary deficiency is uncommon in developed countries; secondary deficiency is more common. Secondary zinc deficiency develops in some patients with hepatic insufficiency (because the ability to retain zinc is lost), patients receiving diuretics, and those with diabetes mellitus, sickle cell disease, chronic renal failure, malabsorption, or stressful conditions (eg, septicemia, burns, head injury). Zinc deficiency is extremely common among elderly institutionalized and homebound patients and patients with lung cancer. Maternal zinc deficiency may cause fetal malformations and low birth weight.
Zinc deficiency in children causes impaired growth and impaired taste (hypogeusia). Other signs and symptoms in children include delayed sexual maturation and hypogonadism. In children or adults, symptoms include hypospermia, alopecia, impaired immunity, anorexia, dermatitis, night blindness, anemia, lethargy, and impaired wound healing. With secondary deficiency, testosterone deficiency, night blindness, apathy, and irritability may develop.
Zinc deficiency should be suspected in undernourished patients with typical symptoms or signs. However, because many of the symptoms and signs are nonspecific, clinical diagnosis of mild zinc deficiency is difficult. Laboratory diagnosis is also difficult. Serum levels are often inaccurate; diagnosis usually requires the combination of low levels of zinc in serum or tissues (eg, in RBCs, WBCs, platelets, saliva, hair, or nails) and increased urinary zinc excretion. If available, isotope studies can measure zinc status more accurately. Treatment consists of elemental zinc 15 to 70 mg/day po for 6 mo.
Acrodermatitis
enteropathica (a rare, once fatal autosomal recessive disorder) causes malabsorption of zinc. The disorder causes psoriasiform dermatitis around the eyes, nose, and mouth; on the buttocks; and in an acral distribution. It causes hair loss, paronychia, impaired immunity, recurrent infection, impaired growth, and diarrhea. Symptoms and signs usually develop after an infant is weaned from breast milk. In such cases, doctors suspect the diagnosis, which is confirmed by measuring a low plasma, WBC, or hair zinc level. Zinc sulfate 30 to 150 mg/day po results in complete remission.
Toxicity:
Toxicity is extremely rare. Ingesting doses of elemental zinc ranging from 100 to 150 mg/day interferes with copper metabolism and causes low blood copper levels, RBC microcytosis, neutropenia, and impaired immunity. Ingesting large amounts (200 to 800 mg/day), usually by consuming acidic food or drink from a galvanized (zinc-coated) container, can cause vomiting and diarrhea. Metal fume fever, also called brass-founders' ague or zinc shakes, is caused by inhaling industrial zinc oxide fumes; it results in neurologic damage. Symptoms resolve after 12 to 24 h in a zinc-free environment.
Last full review/revision November 2005
Content last modified November 2005
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