Tissue Concentration or Intake of Essential NutrientIn absolute deficiency, death results. With limited intake, the organism may survive but biological functions are impaired, thus defining a deficiency state. The plateau of the curve reflects a homoeostatic regulation that is ensures optimal health over a wide range of nutritional intakes.
As the nutrient is given excess, first marginal toxicity is attained followed by mortal toxicity. The basic curve holds true for virtually all essential elements, although the curve may vary quantitatively for each essential nutrient. For many of the elements there is only a 10 to a 100 fold range between survival and the appearance of toxic effects.
Over the past several decades, as analytical detection limits have been lowered, the list of trace and ultra trace elements claimed to be essential for humans and animals has grown steadily.
Characteristic of Trace Element Functions.
Although many details of trace element function are not yet understood, some general characteristics are well known. These are amplification of trace element action, specificity, homeostasis and interactions [Merz, W. Science, 213, 1332 (1981).]
Amplification of Trace Element Action. The action of a very small amount of a
trace element is necessary for optimal performance of the whole organism. Lack of a
small amount of a trace element (e.g. iron) can result in clinical abnormalities (anemia),
seemingly disproportionate to the amount of the element missing.
The basis for this amplification of trace element action is that trace elements are
constituents of, or interact with enzymes and hormones that regulate the metabolism of
much larger amount of biochemical substrates.
If the substrate are also regulatory, the effect is even further amplified.
Specificity of Trace Elements. Essential trace elements are specific for their in vivo functions; they cannot be effectively replaced by chemically similar elements. The essential trace metal or element interacts with electron donor atoms such as nitrogen, sulfur and oxygen; the types of action depend on configurational preferences and bond types.
Homeostasis of Trace Elements. Mechanism that ensure optimal body distribution of an element over a range of intakes, constitute a system of homeostatic regulation for that element. This includes absorption, storage and excretion.
Although many details of trace element absorption processes are still being elucidated, the rate of absorption of a trace element generally decreases with its increasing concentration in the intestinal lumen and associated tissues.
Active transport mechanism involving absorption have been postulated for iron, zinc and copper.
Storage proteins like ferritin and metallothionein, are important in the regulation of iron, zinc, and copper, through their capability to buffer against excess free metal. The principal excretory route for elimination of most trace metals is via the feces. Fecal excretion reflects dietary intake as well as homeostatic regulatory mechanism such as gastrointestinal absorption and endogenous metal secretion into the intestine. Relatively small amounts of trace metals are excreted via the urine, but halides ( iodine and fluorine), as well as boron, chromium and selenium, are effectively eliminated via the urine. Body surface losses of some trace metals, particularly iron, selenium, and zinc, can be appreciable in hot climates or in certain stressful conditions. Menstrual iron loss and seminal zinc loss are also minor but can be significant in some cases.
Interactions of Trace Elements. An overabundance of one trace element can interfere with the metabolic utilization of another element present in normal or marginal concentrations [Levander, O A. et al. American NY Acad. Sci., 355 1, (1980)-[Mills, C F. Fed. Proc. 40,, 2138, (1981)]. Aternatively, the effect of a toxic trace element may be ameliorated by another protective trace element. The addition of large amounts of zinc to a diet, interferes with intestinal copper absorption that result in copper deficiency, in spite of otherwise adequate copper intake.
Hence zinc is said to antagonize copper absorption. Copper deficiency, in turn, is known to provoke iron deficiency and anemia.
Interactions that involve toxic elements include the increased retention of cadmium associated with iron deficiency, and the protective effect of selenium against cadmium and mercury toxicity. Lead and aluminum has a better chance of absorption in an environment deficient in calcium, manganese or zinc. The recognition of the antagonistic relation between minerals may be used for preventive purposes through a screening technique such as hair mineral analysis for early warning signals about the presence of a mineral imbalance or toxic elements [Rees, E. L. J. Orthomol. Psych., 8, 37-43 (1979)]. In the process of rectifying the imbalances by providing foods rich in the deficient element(s) or using supplements, the unwanted toxic mineral may by' replaced' by nutrient elements. Instead of chelation, replacement or displacement therapy may be used [Tamari G. M. Cytobiol. Rev. 3, 176-186 (1986)].
It is now recognized that trace elements can become limiting not only because of environmental deficiencies, but also because of imbalances in diets that in the past has been accepted as adequate.
The period since1973 has also been notable for the increase awareness that anomalies in trace element supply can influence human health and well-being, without necessarily producing diagnostically specific clinical changes.
In addition, it is now recognized that clinical expression of a 'latent'; deficiency or excess is often contingent on variables such as the enhanced growth achieved during rehabilitation following general malnutrition or challenges such as stress, infection or injury.
The fact that the ability of specific populations to tolerate such challenges can be influenced by anomalies in trace elements status, emphasizes the need for maintaining intake within tolerable limits [Trace Elements in human nutrition and health. Prepared in collaboration with the Food and Agricultural Organization of the United Nations and the International Atomic Energy Agency. World Health Organization-Geneva (1996)]
The majority of diseases begin when biochemical imbalances occur at the cellular level. Deficiencies or excesses of metal ions, cause most adverse biological effects.[Williams, D R ed. 1976. An introduction to Bio-Organic Chemistry. P.315]. Occasionally these imbalances actually cause illness; more often they simply hinder the body's efficiency, thereby weakening any number of chemically based immunity processes.
Imbalance of those elements essential to health or interference due to heavy metal accumulation, will leave door open to potential disease; yet more and more research point out that modern health care has the potential to correct these imbalances before disease reaches the stage of physical symptoms.
Mineral imbalance increases vulnerability to disease, aggravates existing diseases, and shorten the life span.
Modern nutrition science has focused on the relationship of diet and nutritional status to the diseases that plague western societies such as coronary heart disease, cancer, and other leading causes of death.
Particularly during the last decade, this has led to expansion of the perspectives of nutrition scientist and the evolution of a new paradigm for understanding nutrition
siloutec on 2010-10-21
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