|What is Zinc?|
Zinc is a cofactor for more than 300 enzymes needed for cell function in the eyes, kidneys, muscles, skin, and bones. As a component of metalloenzymes, zinc provides structural integrity to the enzyme and/or participates directly in the reaction at the catalytic site.
Zinc also serves as a necessary structural component of DNA-binding proteins that affect gene expression (the so-called "zinc finger").
Alcohol dehydrogenase contains four zinc ions per molecule. This enzyme is important in the conversion of retinol to retinal (needed for proper vision). Zinc also appears to provide an additive effect to other antioxidants involved in supporting visual acuity.
Another of zinc's important physiological roles involves cell membranes. Zinc affects the activity of enzymes attached to plasma membranes. Some of these enzymes include alkaline phosphatase, carbonic anhydrase, and superoxide dismutase. Zinc also directly affects cell membranes by stabilizing phospholipids and thiol groups that need to be maintained in a reduced state to prevent peroxidative damage.
As a cofactor for many enzymes, zinc frees the vitamin folate so it can move across cell membranes. It also aids in the manufacture of heme and in essential fatty acid metabolism, and it helps release vitamin A from its storage place in the liver.
Meat, liver, eggs, and seafood are considered good food sources of zinc.
High intakes of zinc for an extended period of time can negatively affect copper absorption. Generally, zinc intake is considered completely safe at levels below 60mg/d.