Trace Elements in Human & Animal Nutrition

Trace Elements in Human & Animal Nutrition
Volume 1, 1987 … Edited by Walter Mertz
U.S. Department of Agriculture

Academic Press, Inc.


The Nature of Trace Elements

“Many mineral elements occur in living tissues in such small amounts that the early workers were unable to measure their precise concentrations with the analytical methods then available. They were therefore frequently described as “traces,” and the term trace elements arose to describe them. This designation has remained in popular usage even though virtually all the trace elements can now be estimated in biological materials with some accuracy and precision.

“At the present time, less than one-third of the 90 naturally occurring elements are known to be essential for life. These consist of 11 major elements, namely, carbon, hydrogen, oxygen, nitrogen, sulfur, calcium, phosphorus, potassium, sodium, chlorine, and magnesium. If the six noble gases are excluded as unlikely to have a physiological function, 73 elements of the periodic system remain and, because of their low concentration in living matter, are termed the trace elements. A logical, permanent classification of the trace elements, other than by chemical characteristics, is impossible at the present state of our knowledge. The past has repeatedly proved wrong the then-existing arbitrary classifications into “essential” and “toxic” elements, and elements have been shifted from the latter into the former category at an increasing rate. It is evident that the number of elements recognized as essential reflects the state of knowledge at a certain point in time. It is logically wrong to establish a category of “toxic” elements, because toxicity is inherent in all elements and is but a function of concentrations to which living matter is exposed. … each element produces toxicity at certain concentrations and is compatible with life at a lower range of exposure.

“Whether this lower range of exposure is only tolerated by the organism or is required to provide a vital function, determines whether an element is essential or not. Essentiality is established when a further reduction below the range of tolerable levels, better termed “range of safe and adequate intakes,” results in a consistent and reproducible impairment of a physiological function.

“During the 1930s a wide range of nutritional disorders of humans and farm stock were found to be caused by deficient or excessive intakes of various trace elements from the natural environment. In 1931, mottled dental enamel in humans was shown by three independent groups to result from the ingestion of excessive amounts of fluoride from the drinking water.

“Metabolic interactions among the trace elements were subsequently shown to be of profound nutritional importance and to involve a wide variety of elements.


“Fluorine being a cumulative bone-seeking mineral, the resultant skeletal changes are progressive. According to the natural course of the disease, skeletal fluorosis may be classified into the following phases: preclinical, musculoskeletal, degenerative and destructive, crippling fluorosis, and complications. … effects depend not only on the total dosage and duration of exposure, but also on associated factors such as nutritional status, functional status of the renal tissue, and interaction with other trace elements. Since the effect of fluorine is cumulative, the less serious consequences occur early in the natural course of the disease. Whatever may be the type of fluorine exposure, the clinical picture in chronic poisoning occurs in a phased manner.

“… Pain is a cardinal feature due to arthritic lesions and to secondary peripheral nerve involvement. … workers at risk: aluminum smelters, phosphate fertilizer, ceramics, steel, glass industries.

“… Fluorine is known to bind calcium in the body, causing ionic calcium to decrease; this, in turn, causes secondary hyperparathyroidism.

“… Some industries discharge fluorine in gaseous or other form, polluting their respective neighborhoods with abnormally high amounts of fluorine, which may result in human and /or cattle disease. The clinical picture is similar to endemic skeletal fluorosis with dental and bone changes. … Waldbott described human fluorosis in the neighborhood of an Ohio enamel factory affecting 23 persons and dogs in the neighborhood. The symptoms were indicative of the preskeletal phase. Urinary fluoride excretion: 0.4 to 2.4 mg/day.

“… Renal stones, reported to be common in endemic fluorosis areas, are capable of accumulating considerable amounts of fluorine. … Although the exact genesis of renal stones in fluorine toxicity is not known, it is conjectured that insoluble calcium fluoride is deposited in the urinary tract as a nucleus around which other salts are deposited.”

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