Zinc functions in many enzymatic reactions and is a component of over 200 enzymes. Besides its role in catalyzing reactions, zinc has a major role in the structure and function of membranes and in regulating gene expression. in other processes, zinc assists in the metabolism of carbohydrates and protein and is involved in the action of hormones such as thymic, insulin, growth and sex hormones. Zinc is found in many body tissues, including the pancreas, liver, kidney, lung, muscle, bone, eye, and endocrine glands.
Zinc is absorbed primarily in the upper jejunum of the small intestine. It is transported into mucosal cells by a pancreatic zinc-binding ligand and picked up by albumin for transport to the liver for subsequent storage or processing.
Other dietary factors may interfere with the absorption of zinc. These include calcium intake, dietary fiber, casein, and copper. Gastrointestinal diseases, such as Crohn's disease, also often affect the absorption of zinc. Zinc is primarily excreted through the intestinal tract.
Zinc deficient diets can lead to a variety of function difficulties, ranging from growth retardation to anorexia to lethargy.
The RDA for zinc is 15 mg for adult males, 12 mg for adult females and children, and 5 mg for infants.
The best source of zinc is oysters. Beef and other red meats are good sources of zinc. Whole grains are sources of zinc, though commercial processing techniques usually slough off the the bran and germ portions of the grain, where zinc is mostly located. Legumes and nuts are also good sources.
Zinc supplementation has been used for pregnancy, immune function, sexual function, rheumatoid arthritis, acne, macular degeneration, and Wilson's disease. The dose of supplementary zinc used for these conditions is usually in the range of 30 to 60 mg.
Zinc is relatively nontoxic. However, excessive intakes (greater than 150 mg per day) could interfere with copper metabolism and cause a copper deficiency. Excessive intake has also been associated with impaired immune function.