Trace elements and cardiovascular diseases

Evidence linking marginal intakes of the trace elements, chromium, copper, zinc and selenium, with abnormal lipid metabolism and ultimately cardiovascular diseases is accumulating from both animal and human studies. Chromium supplementation of normal adult men, as well as diabetics, has been reported to increase high density lipoprotein cholesterol and decrease triglycerides and total cholesterol. Subjects with the highest total cholesterol and triglycerides usually respond the most to supplemental chromium. Improvements in lipid metabolism, as well as those in glucose metabolism, appear to be related to improvements in insulin efficiency due likely to increased receptor number. Animal studies also indicate that improvements in serum cholesterol, aortic lipids and plaque formations due to supplemental chromium are associated with decreased circulating insulin. Insufficient dietary copper also leads to elevated lipid levels and impaired heart function. Animal studies indicate an obvious degradation of the heart muscles. Zinc appears to function in cardiovascular diseases primarily via its antagonism with copper. Selenium may also affect cardiovascular diseases since selenium is postulated to be involved in platelet aggregation. These data demonstrate that the trace elements, chromium, copper, and selenium, have beneficial effects on risk factors associated with cardiovascular diseases suggesting that a decreased risk of cardiovascular disease may be achieved by adequate intake of trace elements.

Micronutrient requirements in older women

The nutritional requirements of older women is an area of great interest because the extended life expectancy leads to an increase in women living into their 80s, 90s, and longer. The recommended dietary allowances (RDAs) and dietary reference intakes (DRIs) are not specific for women living to advanced ages, and little research has been conducted specifically on the micronutrient needs of elderly women. Older adults are at greater risk for nutritional deficiencies than are younger adults due to physiologic changes associated with aging, acute and chronic illnesses, prescription and over-the-counter medications, financial and social status, and functional decline. Among the significant age-associated changes in nutrient requirements, the need for energy decreases and the requirements for protein increase with age. Among the micronutrients, the significant ones that may be associated with deficiencies in elderly women include vitamin B-12, vitamin A, vitamin C, vitamin D, calcium, iron, zinc, and other trace minerals. In old and very old women, these are micronutrients of interest but there is a great need for research to determine appropriate recommendations. The importance of these selected nutrients and the reasons for the likelihood of deficiency are discussed briefly. However, there is little specific information regarding micronutrient requirements for elderly women. One reason for this is the difficulty in conducting reliable and valid studies due to the heterogeneity of older adults and their unique rate of aging associated with their health status, limited income, disability, and living situation.

Mutational analysis of the adcCBA genes in Streptococcus gordonii biofilm formation

Streptococcus gordonii, a primary colonizer, is part of the pioneer biofilm consortium that initiates dental plaque development on tooth surfaces. An insertion of Tn917-lac transposon into the adcR gene produced a biofilm-defective phenotype. S. gordonii adcR is a regulatory gene and is part of an operon (adc) that includes three other genes, adcCBA. AdcC contains a putative consensus-binding site for adenosine triphosphate, AdcB is a putative hydrophobic membrane protein, and AdcA is a putative lipoprotein permease. Mutants were constructed by insertional inactivation in each of the three adcCBA genes and their effects on biofilm formation examined. The adcC::spec(R) and adcB::spec(R) mutations displayed a biofilm-defective phenotype, whereas the adcA::spec(R) mutant was biofilm-positive in a static polystyrene microtiter plate biofilm assay. All three mutants formed poor biofilms in a flow-cell system and were competence-defective, suggesting the adc operon plays an important role in S. gordonii biofilm formation and competence.

Wasted sheep and premature infants: the role of trace metals in hematopoiesis

Trace element deficiencies and toxicities are not commonly encountered in clinical practice, particularly in regions where there is access to adequate nutrition and occupational exposures are regulated. However, specific clinical scenarios associated with trace metal deficiency and toxicity states do exist. Often, clues to the presence of these states may lie in the development of blood count abnormalities. The consultant haematologist is frequently involved in the care of these patients, and it is with this audience that this review is intended. This review will focus on the trace metals required for normal hematopoiesis including their function, metabolism, deficiency and toxicity states, and the clinical situations underlying these. As much of the information regarding trace metal disease states has arisen from veterinary medicine and from human case reports, these will be summarized and highlighted in this review.

[Essential trace metals and brain function]

Trace metals such as zinc, manganese, and iron are necessary for the growth and function of the brain. The transport of trace metals into the brain is strictly regulated by the brain barrier system, i.e., the blood-brain and blood-cerebrospinal fluid barriers. Trace metals usually serve the function of metalloproteins in neurons and glial cells, while a portion of trace metals exists in the presynaptic vesicles and may be released with neurotransmitters into the synaptic cleft. Zinc and manganese influence the concentration of neurotransmitters in the synaptic cleft, probably via the action against neurotransmitter receptors and transporters and ion channels. Zinc may be an inhibitory neuromodulator of glutamate release in the hippocampus, while neuromodulation by manganese might mean functional and toxic aspects in the synapse. Dietary zinc deficiency affects zinc homeostasis in the brain, followed by an enhanced susceptibility to the excitotoxicity of glutamate in the hippocampus. Transferrin may be involved in the physiological transport of iron and manganese into the brain and their utilization there. It is reported that the brain transferrin concentration is decreased in neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease and that brain iron metabolism is also altered. The homeostasis of trace metals in the brain is important for brain function and also for the prevention of brain diseases.

[Function and toxicity of trace metals in the central nervous system]

Trace metals such as zinc, manganese and iron usually serve the function of metalloproteins in neurons and glial cells, while a portion of trace metals exists in the presynaptic vesicles, and may be released with neurotransmitters. Zinc released into the synaptic cleft may serve as an inhibitory neuromodulator of glutamate release in the hippocampus, while neuromodulation by other trace metals such as manganese and copper might mean both functional and toxic aspects in the synapse. Dietary zinc deficiency affects zinc homeostasis in the brain, followed by an enhanced susceptibility to excitotoxicity of glutamate in the hippocampus. The homeostasis of trace metals in the brain is important for brain function and also prevention of brain diseases.

IDENTIFICATION OF TRACE ELEMENT–CONTAINING PROTEINS IN GENOMIC DATABASES

Development of bioinformatics tools provided researchers with the ability to identify full sets of trace element-containing proteins in organisms for which complete genomic sequences are available. Recently, independent bioinformatics methods were used to identify all, or almost all, genes encoding selenocysteine-containing proteins in human, mouse, and Drosophila genomes, characterizing entire selenoproteomes in these organisms. It also should be possible to search for entire sets of other trace element-associated proteins, such as metal-containing proteins, although methods for their identification are still in development.

Nutritional modulation of neonatal outcomes

In humans, growth and development continues until early adulthood when bone, muscle, and nervous tissue reaches final stages of maturity. Adequate levels of nutritional intake and utilization are critical to optimize ongoing growth. The goal of nutritional therapy for premature or ill neonates has been to provide sufficient nutrients to allow growth to continue at rates seen in utero. Functional immaturity of the gut in the premature infant makes absorption and utilization of nutritional substrates difficult. Premature infants are at risk for developing necrotizing enterocolitis, a potentially lethal bowel disorder. The etiology of necrotizing enterocolitis is not well understood, and a number of theories of causation have been proposed. Breast milk, the optimal source of nutrition for the neonate, is believed to confer some protection against necrotizing enterocolitis. A number of breast milk components have been credited with antiinflammatory properties. Breast milk is recognized for its benefits, yet for preterm infants breast milk alone does not promote adequate growth. A number of breast milk supplements have been investigated to facilitate growth and development and to prevent necrotizing enterocolitis. This article addresses development of the fetal gastrointestinal system, focusing on the biological mediators for normal function and the role of human breast milk and its additives in optimizing neonatal growth. The possible etiologies of necrotizing enterocolitis are discussed in terms of the relationship between this disease and enteral feeding practices.

Trace elements in human physiology and pathology. Copper

Copper is a trace element, important for the function of many cellular enzymes. Copper ions can adopt distinct redox states oxidized Cu(II) or reduced (I), allowing the metal to play a pivotal role in cell physiology as a catalytic cofactor in the redox chemistry of enzymes, mitochondrial respiration, iron absorption, free radical scavenging and elastin cross-linking. If present in excess, free copper ions can cause damage to cellular components and a delicate balance between the uptake and efflux of copper ions determines the amount of cellular copper. In biological systems, copper homeostasis has been characterized at the molecular level. It is coordinated by several proteins such as glutathione, metallothionein, Cu-transporting P-type ATPases, Menkes and Wilson proteins and by cytoplasmic transport proteins called copper chaperones to ensure that it is delivered to specific subcellular compartments and thereby to copper-requiring proteins.

Trace elements, innate immune response and parasites

Micronutrient deficiencies and infectious disease often coexist and show complex interactions leading to mutually reinforced detrimental clinical effects. Such a combination is predominantly observed in underprivileged people of developing countries, particularly in rural regions. Several micronutrients such as trace elements (zinc, iron, selenium) modulate immune function and influence the susceptibility of the host to infection. Nevertheless, the effect of individual micronutrients on components of innate immunity is difficult to design and interpret. Micronutrient deficiency, in general, has a widespread effect on nearly all components of the innate immune response. Chagas' disease is a pertinent model to study interaction of nutrition, immunity and infection, as it implies many components of innate immunity. An important question is whether alterations on micronutrient intake modify the course of infection. Some interactions of trace elements with innate immunity and acute inflammatory response are reviewed in this article with a special focus on selenium deficiency and Trypanosoma cruzi infection.

Trace element biology: the knowledge base and its application for the nutrition of individuals and populations

Impressive strides are being made in the understanding of trace element metabolism and function. This is underscored by the many contributions in these proceedings. However, not so impressive are: i) the precise recognition of mild trace element deficiencies and how to establish their functional consequences, possibly confounded by concurrent trace element inadequacies, are difficult to assess, ii) approaches to the quantitative determination of requirements for trace elements remain unsatisfactory and archaic, in so many ways, iii) our understanding of the extent of the biological basis for the variation in requirements among apparently similar individuals is poor, and iv) much needs to be learned about the quantitative extent to which genetic, epigenetic and dietary factors interact to determine the nutritional phenotype. Some ideas are presented as to how we might embrace, in the context of a reconstructive approach, the exciting new knowledge and related techniques emerging during the postgenome era and develop new paradigms for assessing trace element needs and status, and for establishing effective nutrient intake under different conditions of complex genotype-environment interactions. Metabolites are functional cellular entities and I also urge a vigorous application of metabolomics and of metabolic profiling that is closely linked with genomics, proteomics, trace element kinetics and system analysis, as components of the new integrative paradigm. We need to understand the system and its strategy, not only the molecular details of its component parts and its individual controls. An interdisciplinary research and teaching enterprise will be necessary to best achieve this aim. All of this is related to our common goal to promote, through expanded biological knowledge and its effective application, the enhanced role of trace elements for human well-being.

Cellular zinc and redox states converge in the metallothionein/thionein pair

The paramount importance of zinc for a wide range of biological functions is based on its occurrence in thousands of known zinc proteins. To regulate the availability of zinc dynamically, eukaryotes have compartmentalized zinc and the metallothionein/thionein pair, which controls the pico- to nanomolar concentrations of metabolically active cellular zinc. Interactions of zinc with sulfur ligands of cysteines turn out to be critical both for tight binding and creation of a redox-active coordination environment from which the redox-inert zinc can be distributed. Biological oxidants such as disulfides and S-nitrosothiols oxidize the zinc/thiolate clusters in metallothionein with concomitant zinc release. In addition, selenium compounds that have the capacity to form selenol(ate)s catalytically couple with the glutathione/glutathione disulfide and metallothionein/thionein redox pairs to either release or bind zinc. In this pathway, selenium expresses its antioxidant effects through redox catalysis in zinc metabolism. Selenium affects the redox state of thionein, an endogenous chelating agent. With its 20 cysteines, thionein contributes significantly to the zinc- and thiol-redox-buffering capacity of the cell. Thus, hitherto unknown interactions between the essential micronutrients zinc and selenium on the one hand and zinc and redox metabolism on the other are key features of the cellular homeostatic zinc system.

Zinc-altered immune function

Zinc is known to be essential for all highly proliferating cells in the human body, especially the immune system. A variety of in vivo and in vitro effects of zinc on immune cells mainly depend on the zinc concentration. All kinds of immune cells show decreased function after zinc depletion. In monocytes, all functions are impaired, whereas in natural killer cells, cytotoxicity is decreased, and in neutrophil granulocytes, phagocytosis is reduced. The normal functions of T cells are impaired, but autoreactivity and alloreactivity are increased. B cells undergo apoptosis. Impaired immune functions due to zinc deficiency are shown to be reversed by an adequate zinc supplementation, which must be adapted to the actual requirements of the patient. High dosages of zinc evoke negative effects on immune cells and show alterations that are similar to those observed with zinc deficiency. Furthermore, when peripheral blood mononuclear cells are incubated with zinc in vitro, the release of cytokines such as interleukins (IL)-1 and -6, tumor necrosis factor-alpha, soluble IL-2R and interferon-gamma is induced. In a concentration of 100 micro mol/L, zinc suppresses natural killer cell killing and T-cell functions whereas monocytes are activated directly, and in a concentration of 500 micro mol/L, zinc evokes a direct chemotactic activation of neutrophil granulocytes. All of these effects are discussed in this short overview.

Trace metals and the elderly

The elderly are at nutritional risk as a result of multiple physiological, social, psychological, and economic factors. Elderly persons have a higher incidence of chronic diseases and associated intake of medications that may affect nutrient utilization. Social and economic conditions can adversely affect dietary choices and eating patterns. Physiological functions naturally decline with age, which may influence absorption and metabolism. Loneliness and reluctance to eat may complicate an already marginal situation. This article reviews specific trace metals in relation to the elderly. Our objectives are to provide Dietary Reference Intakes for older adults, to provide information on presenting features and functional consequences of trace metal deficiency, and to discuss potential effects and/or benefits of trace metal supplementation in the elderly.

[Transitional elements and free radicals]

Iron and copper are essential trace elements, which in certain conditions, namely in the ionised form or in low-molecular complexes, can participate in single electron reactions and catalyse formation of free radicals, including the dangerous hydroxyl radical. Similar behavior have also some other transitive metals. Our overview is aimed on the role of transitive elements in the formation of free radicals and on the mechanisms that organisms have to prevent it. The highest attendance is given to the metabolism of iron and cooper. Consistent protection against free transitive metals (by binding with proteins, by oxidation or sequestration in a special compartment) enables organism to use their beneficial and required features without impairment of cell. Knowledge of these mechanisms provides the means to predict and effectively prevent the brake down of such defend systems in situations of the intravascular hemolysis, hemodialysis, administration of iron, impairments of the iron and copper metabolism, intoxication by oxidising substances etc.

The role of trace minerals in the pathogenesis of postmenopausal osteoporosis and a new effect of calcitonin

The physiologic role of calcitonin in mineral and bone homeostasis is not very well understood. Very few longitudinal studies have reported the effects of calcitonin therapy on trace minerals in postmenopausal osteoporosis despite the documented involvement of trace minerals in normal skeletal metabolism. Several trace minerals, particularly magnesium (Mg) and zinc (Zn), essential for organic bone matrix synthesis have been known for at least three decades. The present study was designed to determine whether the mineral profile was different between 70 osteoporotic and 30 nonosteoporotic postmenopausal women and to evaluate the efficacy of calcitonin therapy for 6 months on these trace minerals in postmenopausal osteoporotic women. In our study, the serum values of Mg, copper (Cu), and Zn (P < 0.05) were significantly lower in the patient group than those in the control group. After 3 months of treatment, serum Cu, Zn, and Mg levels did not differ between the patients and controls, and this situation has continued after the end of 6 months of therapy. Serum Cu, Zn, and Mg levels increased consistently during the 6-month treatment period. The higher levels of serum Mg in the 3rd and 6th months of therapy were found to be statistically significant compared to those before treatment (P < 0.05). Serum Cu and Zn levels were found to be significantly higher at all measurements during the treatment period as well as at the end of therapy (P < 0.05). These results suggest that (1) calcitonin therapy regulates Mg, Cu, and Zn levels in postmenopausal osteoporosis; (2) when serum calcium and phosphorus were normal in postmenopausal osteoporosis, serum Mg, Cu, and Zn were more useful for evaluation; and (3) further studies are essential to evaluate the role of dietary composition on the manifestations of osteoporosis.

The role of trace elements in psoriatic patients undergoing balneotherapy with Dead Sea bath salt

BACKGROUND

A beneficial effect was observed in patients with psoriasis vulgaris following balneotherapy with Dead Sea bath salt.

OBJECTIVES

To evaluate the possible role of trace elements in the effectiveness of balneotherapy.

METHODS

Serum levels of 11 trace elements were analyzed in 23 patients with psoriasis vulgaris who participated in a double-blind controlled study of balneotherapy with either Dead Sea bath salt (12 patients) or common salt (11 patients). Thirteen healthy volunteers served as controls.

RESULTS

The mean pre-treatment serum levels of boron, cadmium, lithium and rubidium were significantly lower in patients compared to controls, whereas the mean pre-treatment serum level of manganese was significantly higher in patients compared to controls. Balneotherapy with Dead Sea bath salt resulted in a significant decrease (P = 0.0051) in the mean serum level of manganese from 0.10 +/- 0.05 mol/L to 0.05 +/- 0.02 mumol/L. The mean reduction in the serum level of manganese differed significantly (P = 0.002) between responders (% Psoriasis Area and Severity Index score reduction > or = 25) and non-responders (% PASI score reduction < 25). Following balneotherapy with Dead Sea bath salt the mean serum level of lithium decreased in responders by 0.01 +/- 0.02 mumol/L, whereas its level in non-responders increased by 0.03 +/- 0.03 mumol/L. (P = 0.015).

CONCLUSIONS

Manganese and lithium may play a role in the effectiveness of balneotherapy with Dead Sea bath salt for psoriasis.

[Alcohol and nutrition]

Alcoholism and alcohol-associated organ injury is one of the major health problems worldwide. Alcohol may lead to an alteration in intermediary metabolism and the relation between alcohol intake and body weight is a paradox. The effect of alcohol intake on resting metabolic rate, assessed by indirect calorimetry, and lipid oxidation, is still controversial. Small quantities of ethanol seem to have no effect on body weight. Ingestion of moderate amounts may lead to an increase in body weight, via a lipid-oxidizing suppressive effect. Chronic intake of excessive amounts in alcoholics leads to a decrease in body weight, probably via increased lipid oxidation and energy expenditure. Chronic ethanol abuse alters lipid-soluble (vitamins A, D and E) and water-soluble (B-complex vitamins, vitamin C) vitamins status, and some trace elements status such as magnesium, selenium or zinc.

The role of trace elements for the health of elderly individuals

Elderly individuals have a higher risk to develop trace element deficiencies due to modified dietary habits and requirements, age related physiological changes, drug therapy, and chronic diseases leading to or associated with enhanced consumption or excretion of trace elements. This review gives an overview about the role of zinc, iron, selenium, copper, chromium and fluoride for the health of elderly people in regard of physiological functions, trace element status and intake, and effect of supplementation on clinical parameters and disease outcome.

Molecular architecture of the brain microvasculature: perspective on blood-brain transport

Brain endothelial cells and their intercellular tight junctions form a cellular interface between the circulating blood and neural environment. All nutrients consumed by brain must traffic through this cellular space and its two limiting membranes. Additionally, the endothelial cell affects homeostasis by contributing or removing constituents from the interstitial space. These endothelial-cell functions are collectively accomplished with a rich complement of transporters and channels distributed, frequently asymmetrically, between the luminal and abluminal membranes. The identity and characterization of these proteins is rapidly advancing by application of molecular and cellular techniques. Knowledge of these molecular mechanisms will be beneficial in improving brain function and the treatment of neurological diseases.

Trace elements in regulation of NF-kappaB activity

In recent years several studies have shown that NF-kappaB might be a very important therapeutic target in the treatment ot various chronic inflammatory, degenerative and tumour diseases. Trace elements play essential roles in the regulation ot cell signaling mechanisms via transcription tactors and a large number of genes. An important aspect of the present review is the description ot the mechanisms by which trace elements might influence transcription factor NF-kappaB. DNA-binding activity of NF-kappaB is regulated by the redox state of the cysteine residue (Gys-62) in the DNA binding domain of the p50 subunit and impaired by different metals (Go, Cr, Ni, Cd, Pb). It has been hypothesised that the broad speciticity of interrelationships between NF-kappaB. AP-1 and various metals results from interactions of metals with specific moieties of transcription factors and IkappaB-kinases, as well as trom the existence of a metal-governed redox system. The hypothetical targets in the NF-kappaB signaling pathway affected by metals are: IkappaB-kinases, IkappaBs, NF-kappaB, proteasome degradation of NF-kappaB, kappaB-sites in DNA. Possibly, this system is required by the cell for adequate regulation ot the transcription machinery in response to changes in intracellular and intranuclear fluxes of metals and radicals and is very ancient evolutionary mechanism of stress adaptation. The role of the NF-kappaB-mediated mechanism in induction or prevention of chronic intlammatory, allergic, degenerative and tumor diseases by zinc, vanadium, manganese, copper, silica, iodine and other trace elements is discussed.

The importance of selenium to human health

The essential trace mineral, selenium, is of fundamental importance to human health. As a constituent of selenoproteins, selenium has structural and enzymic roles, in the latter context being best-known as an antioxidant and catalyst for the production of active thyroid hormone. Selenium is needed for the proper functioning of the immune system, and appears to be a key nutrient in counteracting the development of virulence and inhibiting HIV progression to AIDS. It is required for sperm motility and may reduce the risk of miscarriage. Deficiency has been linked to adverse mood states. Findings have been equivocal in linking selenium to cardiovascular disease risk although other conditions involving oxidative stress and inflammation have shown benefits of a higher selenium status. An elevated selenium intake may be associated with reduced cancer risk. Large clinical trials are now planned to confirm or refute this hypothesis. In the context of these health effects, low or diminishing selenium status in some parts of the world, notably in some European countries, is giving cause for concern.

The antioxidant properties of zinc

The ability of zinc to retard oxidative processes has been recognized for many years. In general, the mechanism of antioxidation can be divided into acute and chronic effects. Chronic effects involve exposure of an organism to zinc on a long-term basis, resulting in induction of some other substance that is the ultimate antioxidant, such as the metallothioneins. Chronic zinc deprivation generally results in increased sensitivity to some oxidative stress. The acute effects involve two mechanisms: protection of protein sulfhydryls or reduction of (*)OH formation from H(2)O(2) through the antagonism of redox-active transition metals, such as iron and copper. Protection of protein sulfhydryl groups is thought to involve reduction of sulfhydryl reactivity through one of three mechanisms: (1) direct binding of zinc to the sulfhydryl, (2) steric hindrance as a result of binding to some other protein site in close proximity to the sulfhydryl group or (3) a conformational change from binding to some other site on the protein. Antagonism of redox-active, transition metal-catalyzed, site-specific reactions has led to the theory that zinc may be capable of reducing cellular injury that might have a component of site-specific oxidative damage, such as postischemic tissue damage. Zinc is capable of reducing postischemic injury to a variety of tissues and organs through a mechanism that might involve the antagonism of copper reactivity. Although the evidence for the antioxidant properties of zinc is compelling, the mechanisms are still unclear. Future research that probes these mechanisms could potentially develop new antioxidant functions and uses for zinc.

Evolutionary events culminating in specific minerals becoming essential for life

The environment in which living organisms evolved was apparently a primary determinant of which elements became essential for life. The first organic materials and, ultimately, life forms most likely were formed in an ancient sea containing minerals that provided structural integrity and catalytic ability to the first complex organic substances. The site at which life began has been suggested to be at the edge of the sea near sediments, or around a hydrothermal system. The strongest circumstantial evidence supports a hyperthermophilic beginning. Regardless of the site, the biological importance of elements tends to parallel oceanic abundance, but in higher forms of life this parallelism apparently has been mitigated by a natural selection process that resulted in some elements becoming more important because of their superior abilities over other elements to perform vital functions. The converse to biological importance is that toxicity of elements and oceanic abundance tends to be inversely related. The basis for this relationship may be that the efficiency of homeostatic mechanisms to cope with a high intake of a specific element probably reflects upon the exposure of an organism to the element during its evolution. Thus, a study of evolutionary events may be helpful in predicting and comprehending the essential and toxic nature of mineral elements in humans.

Effects of stair-step nutrition and trace mineral supplementation on attainment of puberty in beef heifers of three sire breeds

A study was conducted to evaluate the influence of nutrition and sire breed on age at puberty and first lactation milk yield in crossbred beef heifers. After weaning, 208 heifers sired by Hereford, Limousin, or Piedmontese bulls were assigned to either a control (CG) or stair-step gain (SSG) dietary regimen plus a mineral supplement with or without Cu, Zn, and Mn top-dressed onto the feed. Heifers on the SSG regimen were fed a diet intended to supply energy to support gains at a rate of 120% of the CG diet for 55 d and then were switched to a diet formulated to produce an ADG at 70% of the rate of the CG diet for 84 d. They then switched back to the 120% diet for the last 30 d before breeding. Total weight gain and overall rate of gain did not differ among dietary treatments. Hereford- and Limousin-sired heifers gained at similar rates, and Piedmontese-sired heifers gained an average of .10 kg/d slower than the other two sire breed groups. During one period, Piedmontese-sired heifers on the CG diet gained .19 kg/d faster ( P < . 01) when supplemented with mineral than when not. During that same period, there was no influence of mineral supplementation on weight gains for Hereford- or Piedmontese-sired heifers on the high SSG diet, but Limousin-sired heifers tended (P = .07) to gain faster (1.00 vs .85 kg/d) when supplemented with Cu, Zn, and Mn than when not. Piedmontese-sired heifers reached puberty at the earliest age (P = .03), followed by Hereford- and then Limousin-sired heifers. There were no treatment effects on milk yield at an average of 70 d of lactation. However, at approximately 120 d of lactation, Piedmontese-sired heifers were producing less milk (P < .05) than Limousin- but not Hereford-sired heifers. Hereford-sired heifers had lower (P < .05) plasma Cu concentrations than Piedmontese-sired heifers. There were no treatment effects on plasma Zn concentrations. Heifers sired by bulls of breeds that differ in potential muscularity differed in growth, reproduction, milk yield, and plasma mineral concentrations, but dietary treatments resulted in little to no differences in these variables.

Trace minerals in human growth and development

Trace mineral deficiencies may affect several biological functions in humans, including physical growth, psychomotor development and immunity. We have reviewed the mechanisms whereby several trace mineral deficiencies may affect these biological functions at different ages (fetal life, infancy, childhood and adolescence), as well as the evidence supporting this association. We describe the effects of zinc deficiency on the hormonal regulation of growth and sexual development in both humans and animal models. We provide data regarding the effects of iron deficiency on growth and psychomotor development. We mention the effects of copper, manganese, selenium and iodine deficiencies on growth and development. We conclude that iron deficiency may affect psychomotor development, but does not appear to affect growth. Zinc deficiency may cause growth retardation and psychomotor delay.

Micronutrients in fetal growth and development

The roles that the different vitamins and minerals play in fetal growth and development are reviewed, primarily with respect to growth and differentiation in humans; but, as appropriate, data provided from animal and cellular studies are also considered.

Role of micronutrients in sport and physical activity

Many micronutrients play key roles in energy metabolism and, during strenuous physical activity, the rate of energy turnover in skeletal muscle may be increased up to 20-100 times the resting rate. Although an adequate vitamin and mineral status is essential for normal health, marginal deficiency states may only be apparent when the metabolic rate is high. Prolonged strenuous exercise performed on a regular basis may also result in increased losses from the body or in an increased rate of turnover, resulting in the need for an increased dietary intake. An increased food intake to meet energy requirements will increase dietary micronutrient intake, but athletes in hard training may need to pay particular attention to their intake of iron, calcium and the antioxidant vitamins.

Trace elements and apoptosis

It is known that apoptosis is considered to be responsible for selective deletion of cells during embryogenesis, the homeostasis of cell populations in continuously renewing tissues (i.e., serving as a counterbalance to mitosis), and tissue involution in response to chemical or physical stimuli. There are many publications on these questions. On the other hand, the intracellular processes that contribute to apoptosis are incompletely understood. Therefore, the role of apoptosis in the intracellular accumulation and outflow of minerals is of considerable importance in light of both their essential functions and toxic effects.

Review of the scientific basis for establishing the essentiality of trace elements

The recent Expert Consultation of World Health Organization (WHO)/Food and Agricultural Organization (FAO)/International Atomic Energy Agency (IAEA) defined essentiality of a trace element as follows: "An element is considered essential to an organism when reduction of its exposure below a certain limit results consistently in a reduction in a physiologically important function, or when the element is an integral part of an organic structure performing a vital function in the organism." This definition omits a previous postulate that the mechanism of action of an essential trace element should be well defined; it also supersedes another criterion, once suggested for essentiality, a normal, rather than log-normal distribution of an element's tissue concentrations. The Expert Consultation offers no generally applicable criteria for the physiological importance of functions, and that determination is left to expert groups charged with setting national and other nutritional recommendations. The use of the term "physiological" rather than "biochemical" strongly implies that neither changes of an element's concentration nor of a specific enzyme function alone are proof of essentiality. Among physiologically important functions are growth, reproduction, longevity, and all metabolic and hormonal functions that bear a clear, inverse relation to disease risk. Finally, the term "consistent" states the need for independent confirmation of the original data, before an element can be recognized as essential. These definitions will be discussed as background for further discussions of our present knowledge of boron (B).

[Aluminum and the human body]

Aluminium is one of the trace elements in the human organism the presence of which is described as contamination. The authors describe the toxic action in subjects working in an environment contaminated with powdered aluminium or its compounds. Non-professional exposure is observed in subjects with renal failure as aluminium is retained, in particular in case of concurrent antacid therapy on the basis of aluminium salts. Dialyzation encephalopathy may develop, aluminium osteopathy and microcytic anaemia. The most effective prevention is dialysis using a dialyzation solution with a low aluminium content and elimination of aluminium binding phosphates. The results of hitherto accomplished studies call for further research into the action of this element on the human organism.

[Trace elements and trace element therapy update]

Starting from the importance of the trace elements in basic biochemical mechanisms from the human organism, the present role of trace elements therapy, as part of allopathic therapy, is discussed. The ideal properties of trace elements, the therapeutic concepts regarding trace elements, the main pharmaceutical forms that contain them, and their most important uses are presented.