Zinc

• Zinc is a component in over 200 proteins, mostly of them enzymes. Recall superoxide dismutase where Zn²⁺pairs with Cu²⁺ in the catalytic site. Muscles contain over 60% of the zinc in the body. Cells and tissues with high zinc concentration: red and white blood cells, liver, kidney, pancreas, bones, skin, retina, prostate.
• Involved in the thyroid hormone metabolism (1). Zinc deficiency was found to lower the serum level of triiodothyronine in patients with hepatic and gastrointestinal disorders (2).
• Involved in insulin and steroid hormone metabolism. For instance, the glucocorticoids (a class of steroids that mainly affect carbohydrate metabolism) bind to their receptor and this complex interacts with a region of a DNA-bound protein. This protein contains the so-called "zinc fingers", which are amino acid motifs that fold around one or more zinc ions. By binding to specific DNA sequences these zinc fingers can activate the transcription of certain genes to elicit a response to the hormonal signal. Zinc fingers have also been shown to mediate protein-protein and protein-lipid interactions (3).
• Required for nucleic acid synthesis and cell growth. Plays an important role in immune function, wound healing.
• Interactions: High fiber and calcium intake as well as high iron to zinc ratio decrease zinc absorption. Zinc-rich foods should be taken apart from high-fiber foods.
• Health benefits: It is now widely accepted by nutritionists that a sizeable proportion of the population in the developed world has some form of zinc deficiency. Because of zinc involvement in several critical points of metabolism and the implications for human pathology there is a need for understanding of zinc biochemistry and homeostasis at molecular, cellular and organ-system level as well as of the factors that affect its bioavailability (4). Supplementation has been found useful in: rheumatoid arthritis and irritable bowel syndrome, acute infections, acne, Alzheimer's and Wilson's disease. In vitro studies (a cell-culture model) showed that low intracellular zinc levels increased oxidative stress and DNA single-strand breaks. In zinc deficiency there is an increased expression of DNA repair proteins as well as a decreased binding of transcription factors such as p53, nuclear factor B and activation protein 1. Repletion with zinc reversed these negative trends (5).
• Best food sources: Oysters, fish, red meat, nuts, whole grains, oats.