Dietary requirements trace elements

Cobalt, copper, molybdenum, iodine, iron, manganese, nickel, selenium, and zinc are sometimes provided to mminants. Mineral deficiency or toxicity in sheep, especially copper and selenium, is a common example of dietary mineral imbalance (21). Other elements may be required for optimal mminant performance (22). ExceUent reviews of trace elements are available (5,22). 

The essential mineral nutrients are classified either as principal elements or as trace and ultratrace elements. The distinction between these groups is the relative amounts ia the dietary requirement (see Table 1). 

Zinc is an important trace element required for all healthy plants and animals. Zinc is found in proteins, such as meats, fish, eggs, and milk. About 10 to 15 miUigrams of zinc is required per day, and it may be taken as a dietary supplement. Zinc helps the blood in our bodies move the waste gas—carbon dioxide—to the lungs and helps prevent macular degeneration (loss of vision). 

A second dietary trace element, selenium, is also essential for normal thyroid hormone metabohsm. Selenium in the form of selenocysteine is a required component for three enzymes that remove iodide from thyroid hormones. Deiodination is the major metabohc pathway by which T4 and T3 are cleared from the system. After secretion by the thyroid gland, T4 may be deiodinated to yield either T3 or the physiologically inactive reverse Tj (3,3, 5 -triiodothyronine, or rX3). T3 and rTj are further deiodinated to form less active metabolites. Selenium, like iodine, is deficient in many areas of the world. 

It is an essential trace element for mammals, but little is known about its role or requirement in human metabolism. In humans, serum levels of nickel are about 1.1 to 1.6 mcg/1. This level increases in conditions such as stroke and acute myocardial infarction. A dietary requirement for adults is about 30 meg/day. 

Klevay, L.M. Dietary Copper and Copper Requirements in Man, in Trace Element Metabolism Man and Animals (M. Kirchgessner, editor), p. 307. Institut fur Emahrungsphysiologie Technische Universitat Munchen, Freising-Weihenstephan, Germany, 1978. 

Deficiency syndromes of Zn, Cu, Cr, Se and Mo have occurred in patients on total parenteral nutrition (TPN). There is still much research to be done in assessing the nutritional status of many elements and understanding their metabolism, so that normal dietary intake may be supplemented for health benefits. Table 2 is a summary of the amounts required, the functions and the nutritional (usually dietary) imbalances in humans, where known, of the essential trace elements.31-33 (Note that this summary does not attempt to include imbalances related to environmental toxicology and occupational hazards.) Several trace elements have important functions in the immune system. Some are associated with nucleic acid. Others have structural roles, such as Si in cartilage, F and Zn in bone. They may be parts of vitamins, such as Co in vitamin B12, or hormones, such as iodine in thyroid hormones, Zn and Cr have a role in the synthesis and action of insulin.31-33... 

An enzyme cofactor can be either an inorganic ion (usually a metal cation) or a small organic molecule called a coenzyme. In fact, the requirement of many enzymes for metal-ion cofactors is the main reason behind our dietary need for trace minerals. Iron, zinc, copper, manganese, molybdenum, cobalt, nickel, and selenium are all essential trace elements that function as enzyme cofactors. A large number of different organic molecules also serve as coenzymes. Often, although not always, the coenzyme is a vitamin. Thiamine (vitamin Bj), for example, is a coenzyme required in the metabolism of carbohydrates. 

Krachler et al. [91] carried out total determinations of trace elements (Ba, Be, Bi, Cd, Co, Cs, Cu, La, Li, Mn, Mo, Pb, Rb, Sb, Sn, Sr, Tl, and Zn) by Q-ICP-MS in 13 formulas based on cow s and soy milk and also in Austrian cow s milk. Some essential elements, such as As, Cr, Se, and V, suffered from serious interferences from polyatomic ions and could not be determined under routine conditions by Q-ICP-MS. In this study, the authors determined only those elements for which isotopes free from serious interferences were available. Concentrations of trace elements such as Cu, Mn, and Zn in the formula powders varied considerably. As pre-formulas and follow-up formulas are partly supplemented with these essential trace elements, their concentrations proved to vary considerably depending on the commercial brand. Also, concentrations of all trace elements quantified were lower in cow s milk than in formulas, which did not meet the dietary requirements of infants. 

Vitamins are organic compounds necessary for growth and health and cannot be synthesized in sufficient quantities for physiologic health by the body. Therefore they must be obtained from food sources or supplementation. Inorganic essentials (minerals are trace elements) are required in much smaller quantities than vitamins. In general, minerals and trace elements aid and support physiologic functions and, like vitamins, must be obtained from dietary soinces. 

Tn recent years there has been an increased interest in assessing the human health effects from environmental exposure to trace metals. Studies of occupational exposures and dietary intakes of trace metals have required the refinement and development of analytical techniques for the analyses of low elemental concentrations in complex matrices. Molybdenum is one of the trace metals that has been the subject of intensive study because it is an essential trace element in both plant and animal nutrition. It is an integral constituent of several metalloenzymes including xanthine oxidase, which is the last enzyme in the catabolic pathway of purines. Extensive ingestion of molybdenum has been shown to cause molybdenosis in cattle. Many of the features of this condition can be ascribed to induced copper deficiency. Whether biochemical changes or adverse health effects in humans can be attributed to excessive exposure to molybdenum is not known. 

Adequate supplies of vitamins and trace elements are extremely critical in maintaining the health and development of humans. These nutrients occupy the attention of those concerned with the physical well being of a public made increasingly aware of the need for the quality and the quantity of their dietary intake. The general principle regarding assessment of nutritional status is to determine the extent to which the metabohc demand for nutrients has been or is currently being met by the supply. In clinical practice, this requires balancing supply and demand. 

More than 15 additional trace elements are considered by some investigators to have a potentially important role in human medicine. A review by Nielsen considers these in detail and discusses emerging concepts of essentiality. For some such as lead, cadmium, arsenic, aluminum, and nickel, the clinical laboratory will primarily consider them as toxic elements (see Chapter 35). Others, such as lithium and fluoride, are classified as pharmacologically beneficial and monitoring of dosage may be required. Some elements can be considered nutritionally beneficial and are reported to produce restorative health effects at lower dosages. Evidence comes mainly from animal studies when dietary depletion of the element is combined with other metabohc, hormonal, or physiological stressors. ... 

The trace elements can be classified into several categories (see table). In 1989, the National Research Council recognized that iron, iodine, zinc, selenium, copper, chromium, manganese, and molybdenum were dietary essentials for humans. Fluorine is also considered to be valuable for human health, because of its benefits to the teeth and skeleton. These nine trace elements are required by humans and other animals because they are essential components in metalloen-zymes and hormones or because they promote health in a specific tissue (such as fluorine in the teeth and skeleton). The trace elements required by the human body in milligram quantities include iron, zinc, copper, manganese, and fluorine. Trace elements required in microgram (jjug) quantities... 

Soil plays an integral part in our lives and is inherently linked to public health. For example, many of the essential trace elements which we require in our diet to remain healthy are derived from soils and parent rock material, and low concentrations or the unavailability of these elements in soil can cause dietary deficiencies. Soils can also be contaminated with a range of potentially hazardous substances (both chemical and biological) which, if present at sufficiently elevated levels, can present a potential public health problem. For example, soils may contain elevated levels of heavy metals such as cadmium and lead which can have measurable and often severe effects on local populations. The soils of Cappadocia in central Turkey are naturally rich in fibrous asbestos-like minerals that are thought to be the cause of a rare cancer in local communities1 while exposure to the bacterium Clostridium tetani in soils can cause tetanus. Despite such examples, the effects of contaminated land have, until recently, been relatively ignored and, even today, our understanding of the mechanisms and level of risk associated with contaminated land is poor in relation to air and water. 

Vitamins and trace elements are collectively dc.scribed as micronutrients , not because they are of limited importance but because they are required in relatively small amounts. Recommended dietary allowances (RDAs) have been defined for most nutrients and these are used in the make up of artificial diets. 

Turnlund JR, Keyes WR and Peiffer GL (1993) A stable isotope study of dietary molybdenum requirements of young men. In Anke M, Meissner D and Mills CF, eds. Trace elements in Man and Animals TEMA 8, pp. 189-192. Verlag Media Tou-ristik Gersdorf Germany. 

Levander OA (1987) Dietary Selenium Requirements Minimal and Optimal Intake and Disadvantages in the Use of Supplements. 2nd Nordic Symposium on Trace Elements in Human Health and Disease, Odense. Abstract Mini-Symposium No. 12 and Round-Table Discussion on Mineral Supplementation. WHO Regional Office for Europe, Copenhagen. Environ Health 26 87-90. 

PDDR (Provisional Daily Dietary Requirement) Daily dose of an essential trace element required for optimal physiological performance of an organism. 

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