See also separate articles on Zinc Deficiency and Zinc Supplements.
Zinc is an essential mineral that is important for immune function, wound healing, normal taste and smell, and is needed for DNA synthesis. Zinc also supports normal growth and development during pregnancy, childhood, and adolescence. However, excessive quantities of zinc intake may lead to both acute and chronic toxicity. The UK recommended ranges for zinc intake are 5.5-9.5 mg/day for males and 4.0-7.0 mg/day for females. A total daily zinc intake of up to 50 mg/day is considered safe.
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Risk factors for zinc excess
- Ingesting zinc in large amounts may occur by consuming acidic food or drink from a galvanised container or by ingestion of excessive quantities of zinc supplements.
- Zinc salts are used in soldering, cement additives, horticultural chemicals and dry cells. Zinc phosphide is used as a rodenticide.
- Inhalation of zinc fumes may cause metal fume fever. Metal fume fever can follow inhalation of fumes of zinc, copper, magnesium, aluminium, antimony, iron, manganese and nickel during welding, galvanising or smelting.
- The intake of zinc from drinking water is very low but may be increased by zinc contamination from pipes and contaminated wells. The UK current regulatory limit in water is 5 mg/L.
- Many cases of zinc poisoning from food have resulted from the storage of food or drink in galvanised containers.
- Zinc may accumulate in acute renal failure.
- Sufferers from haemochromatosis may absorb larger amounts of zinc.
- Zinc toxicity has been seen in both acute and chronic forms. Toxicity from chronic ingestion of zinc usually presents with the features of copper deficiency.
- Ingesting 200 to 800 mg/day of zinc can cause abdominal pain, nausea, vomiting and diarrhoea. Other reported effects include gastric irritation, headache, irritability, lethargy, anaemia and dizziness.
- Prolonged intake of zinc ranging from 100 to 150 mg/day interferes with copper metabolism and causes low copper status, reduced iron function, red blood cell microcytosis, neutropenia, reduced immune function and reduced levels of high-density lipoproteins (it has therefore been suggested but not proven that excessive zinc intake is atherogenic).
Metal fume fever
- Only occurs with the oxide of zinc and not with other zinc compounds. May also occur with other metal oxides.
- Occurs if the zinc oxide is inhaled and not with ingestion or parenteral exposure.
- Symptoms may occur within 3-10 hours of exposure and usually resolve within 1-2 days.
- Cough, dyspnoea, sore throat, chest tightness, headache, fever, rigors, myalgia and arthralgia may occur.
- Other reported symptoms include a metallic taste, nausea, vomiting and blurred vision.
- Blood zinc levels can be measured to assess toxicity.
- Blood zinc levels are generally reliable but may be affected by other factors, eg lowered in acute infection and after trauma, and hypoproteinaemia spuriously lowers plasma-zinc concentration.
Further reading & references
- Food Standards Agency; Zinc
- Toxbase®; (Registration is free for doctors who are employed by an NHS practice.)
- British National Formulary
|Original Author: Dr Colin Tidy||Current Version: Dr Colin Tidy|
|Last Checked: 22/03/2010||Document ID: 571 Version: 22||© EMIS|
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