Principles of Biochemistry Volume 3 - A. Lehninger 1985

Selected Aspects of Human Biochemistry
Human Nutrition
Zinc and Certain Other Trace Elements as Essential Dietary Components

Zinc is known to be a component of the prosthetic groups of more than 80 Enzymes, such as Alcohol dehydrogenase, Carbonic anhydrase, DNA and RNA polymerases, and carboxypeptidase. High concentrations of zinc are found in the Prostate Gland, spermatozoa, and eye Tissues, where it performs important yet still poorly understood Functions. Endemic zinc deficiency has been discovered in some rural areas of Iran. It manifests as short stature, anemia, low serum albumin levels, and delayed Development of the Reproductive System. This zinc deficiency is caused by the consumption of a traditional local dish—unleavened bread made from partially milled flour, which contains a high concentration of phytate (Fig. 26-24); phytate binds very tightly to zinc, thereby hindering its intestinal absorption. An unusual and rather rare manifestation of zinc deficiency in individuals is an impaired perception of taste and smell. Some odors are distorted to such an extent that ordinary food or cooking aromas seem repulsive, resulting in food aversion and, consequently, severe weight loss. Adults need a Dietary intake of at least 15 mg of zinc per day; pregnant and lactating women require higher amounts (Table 26-2). Zinc is abundant in meat, eggs, seafood, milk, and Liver, but is scarce in fruits and green vegetables.

Rats, chicks, and other experimental animals raised under sterile conditions in plastic cages devoid of trace metal residue, and provided only with distilled Water, filtered air, and highly purified diets, also require certain other

Trace Elements for proper growth and vitality. For the most part, these elements are also essential for humans. They include tin, nickel, vanadium, chromium, and silicon, which is necessary for the proper growth of bones and Connective Tissues. Cobalt is an integral part of the vitamin B₁₂ molecule and is therefore essential for microorganisms that produce this vitamin. Cobalt is also required by certain animals, apparently for the synthesis of vitamin B₁₂ by gastrointestinal microorganisms. Selenium, an important component of the enzyme Glutathione peroxidase, and molybdenum, a constituent of the prosthetic groups of xanthine oxidase and aldehyde oxidase, are likewise essential for animal and human organisms. In excess, selenium is highly toxic. In certain areas of the western United States and New Zealand, an excess of selenium in the soil and plants causes a condition known as blind staggers in horses and alkali disease in cattle. Elements such as copper, cobalt, zinc, manganese, and nickel, although essential dietary components, are poisonous in excess and pose a health hazard to workers in the mines where they are extracted and in the metallurgical plants where they are handled regularly.