Zinc-Zinc (abbrev. Zn) is a blue-white element necessary in trace amounts in the body, and is thus referred to as a required trace element. Zinc is required as a cofactor for the optimum functioning of dozens of human enzymes. For example, the enzyme carbonic anhydrase, which plays an integral role in carbon dioxide metabolism, requires zinc to catalyse these reactions. Zinc also has a role in proper cell division and protein synthesis. Therefore, deficiencies of zinc can lead to anaemia, shorter stature, impaired wound healing, and other maladies. Zinc is found in most tissues throughout the human body, but the highest amount is in the choroid of the eye. Therefore, there is some speulation about the importance of zinc and its role in delaying or inhibitin macular degeneration, or merely in maintenence of choroidal health.

The total amount of zinc found in the average individual is more than 2 grams. Although the highest concentration of zinc is found in the choroid, most of the zinc store in the body is found in the bones. The amount of zinc absorbed by the gut is controlled by the normal homeostatic mechanisms, and dietary factors. For example, phytate and other components of dietary fibre bind to zinc, inhibiting its absorption into the gut and facilitate its excretion via the faeces. Although, clinically, this has not been proven to lead to chronic deficiency states, this may contribute to dietary deficiency in impoverished countries, disease states, or in individuals who consume excessive amounts of bran and other cereals.

RDA of zinc

The RDA of zinc is approximately 15mg. Normal human diets provide between 10-20mg daily.

Toxicity of zinc

Although zinc is required in the diet, it can also lead to illness if toxic levels are achieved through ingetsion. Zinc also comes complexed in many forms (eg., salts) and ingestion of these forms not intended for human consumption can lead to illness resembling lead poisoning. Ingestion of excessive amounts of zinc supplements can lead to nausea, vomiting and fever, but is reversible with cessation of toxicity.

Sources of zinc

Good sources of zinc are meats (up to 5mg/100g in weight per meat), whole grains and legumes. Oysters are exceedingly rich in zinc, providing 70mg per 100 grams of oyster !