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Zinc.

Article Excerpt
KEY POINTS

* Zinc is an essential nutrient, required for numerous metabolic functions, including gene expression, growth and immunity.

* Manifestations of zinc deficiency include growth retardation, high rates of infection, skin lesions and impaired wound healing.

* Zinc deficiency is a major contributor to the burden of disease in developing countries.

* Seafood and red meat are good sources of bioavailable zinc. Dietary zinc from plant sources is less bioavailable due to the interaction with phytate.

* The recommended dietary intake for zinc is 8 and 14 mg/day for women and men, respectively The Dietary Guidelines for Australian Adults identify red meat as a substantial source of zinc.

INTRODUCTION

Zinc is involved in a number of metabolic processes, including protein and nucleic acid synthesis, and for the synthesis and action of insulin. It is the most common catalytic metal ion in the cytoplasm of cells. Carbonic anhydrase was the first discovered zinc metalloenzyme; other enzymes include: carboxypeptidase, alkaline phosphatase, DNA/RNA polymerase and superoxide dismutase. (1-3) As a component of enzymes, known as metalloenzymes, zinc participates in the reaction at the active site or provides structural integrity to the enzyme. Genes such as those involved in the regulation of redox state, fatty acid metabolism, signal transduction and platelet activation have been recognised as potential candidates for regulation by zinc: some genes are positively affected, and others negatively; whereas some are affected only by extremes of zinc status. Zinc-containing proteins in the human genome, known as 'zinc fingers', are able to interact with DNA and act as transcriptional mediators. (1,2) Zinc serves as a structural component that allows for the coordinate binding of amino acids, mainly cysteine and histidine residues in the protein chain, to form a finger-like structure.

Adult humans contain 1.5-2.5 g of zinc, which is distributed in all tissues but mostly in fat-free mass such as bones and muscles. Dietary zinc is absorbed mainly from the duodenum by active and passive mechanisms. Once absorbed, zinc is transported to the liver bound to albumin. The major route of zinc excretion is by the intestine, followed by the kidneys. Smaller amounts of zinc are shed in skin cells or secreted by the prostate gland. (1-3) With this background, this paper discusses zinc deficiency, reviews food sources of zinc, and comments on the role of red meat in providing zinc in the overall diet.

ZINC DEFICIENCY

A number of conditions...