Scottish Trace Element and Micronutrient Reference Laboratory
Scotland's specialised laboratory for trace elements and vitamins in health and disease
Zinc (Zn)
This essential element is of established importance in both human and animal nutrition. Zinc deficiency restricts growth and normal development. Numerous enzymes are zinc metalloproteins and many stages of both protein and nucleic acid synthesis are dependent on zinc metalloenzymes.
In malnourished children the rate of regain of lean body mass is related to the level of dietary zinc provision. The existence of marginal zinc depletion in the general population has been postulated and associated with growth retardation, reduction in immune-competence, delayed wound healing, and defects of the special senses (night vision, taste and smell). Increased losses of zinc occur in catabolic states after injury and/or infection. Failure of adequate zinc supply during the recovery phase when there is tissue regrowth, can precipitate acute signs of zinc deficiency. This has been particularly observed when intravenous feeding is used with inadequate zinc content. Signs and symptoms include a localised skin rash (acrodermatitis), abdominal pain with diarrhoea, and mental 'lethargy'. An identical presentation is noted in children with a congenital defect of intestinal zinc absorption, a condition know as acrodermatitis enteropathica, which responds dramatically to oral zinc supplementation. Disorders of zinc metabolism secondary to the primary disease have been reported in alcoholic cirrhosis, inflammatory bowel diseases, diabetes, renal disease and many other conditions. The significance of these observations is unclear.
A condition called "Zinc fume fever" from inhalation of zinc oxide fume is recognised as an occupational hazard. It is found, for example, amongst welders trying to weld galvanised steel. The symptoms, chills, fever, headaches, nausea, thirst, cough and pain in the limbs, resemble those of influenza. Recovery is rapid, usually within 24 hours and always within 48 hours. Fumes of other metals, especially copper and magnesium, can cause similar effects.
Zinc Metabolism
The dietary intake of zinc is around 10-15 mg/day. It is present in meat and other protein foodstuffs, but intestinal absorption is affected by other dietary constituents. Absorbed zinc enters the liver where it is incorporated into zinc metalloenzymes and exported to peripheral tissue in plasma, bound to albumin. Of the total plasma zinc concentration of 12-25 µmol/l, over 90% is associated with albumin, <10% with alpha-2 macroglobulin, and a small amount, <1%, complexed to amino acids and other low molecular weight species.
Zinc homeostasis is achieved by regulation of enterohepatic re-circulation. An amount of zinc equivalent to the total absorbed zinc is re-excreted into the gut in intestinal fluids. In normal health zinc output by the gut is equal to the total dietary intake. Urinary excretion of zinc is low (around 10 µmol/day), and does not vary markedly with dietary supply. It is increased in catabolic states, by certain drugs and/or chelating agents.