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Essential elements4/6/2023 ![]() ![]() This is why common table salt is “iodized”: a small amount of iodine is added. It was not until the 19th century, however, that trace amounts of iodine were found to eliminate goiter (an enlarged thyroid gland). In the 17th century, anemia was proved to be caused by an iron deficiency and often was cured by supplementing the diet with extracts of rusty nails. Because the body’s mechanisms for extracting potassium and calcium from foods are not 100% selective, small amounts of rubidium and strontium, which have no known biological function, are absorbed.īecause it is difficult to detect low levels of some essential elements, the trace elements were relatively slow to be recognized as essential. Examples are rubidium and strontium, whose chemistry is similar to that of the elements immediately above them in the periodic table (potassium and calcium, respectively, which are essential elements). Finally, measurable levels of some elements are found in humans but are not required for growth or good health. The remaining essential elements-called trace elements-are present in very small amounts, ranging from a few grams to a few milligrams in an adult human. The six macrominerals are present in the body in somewhat smaller amounts than the bulk elements, so correspondingly lower levels are required in the diet. In addition, phosphorus is a key constituent of both DNA and RNA: the genetic building blocks of living organisms. Six other elements-sodium, magnesium, potassium, calcium, chlorine, and phosphorus-are often referred to as macrominerals because they provide essential ions in body fluids and form the major structural components of the body. These five elements also constitute the bulk of our diet tens of grams per day are required for humans. Note that most living matter consists primarily of the so-called bulk elements: oxygen, carbon, hydrogen, nitrogen, and sulfur-the building blocks of the compounds that constitute our organs and muscles. The approximate elemental composition of a healthy 70.0 kg (154 lb) adult human is listed in Table 1.6 "Approximate Elemental Composition of a Typical 70 kg Human". This level is the minimum required intake of element E. If the animals do not grow normally on a low-E diet, then their diets are supplemented with E until a level is reached at which the animals grow normally. If the animals grow normally on a diet that is as low as possible in E, then either E is not an essential element or the diet is not yet below the minimum required concentration. Ultraclean environments, in which plastic cages are used and dust from the air is carefully removed, minimize inadvertent contamination. ![]() Scientists determine whether an element is essential by raising rats, chicks, and other animals on a synthetic diet that has been carefully analyzed and supplemented with acceptable levels of all elements except the element of interest (E). An element is considered to be essential if a deficiency consistently causes abnormal development or functioning and if dietary supplementation of that element- and only that element-prevents this adverse effect. Because of the experimental difficulties involved in producing deficiencies severe enough to cause death, especially for elements that are required in very low concentrations in the diet, a somewhat broader definition is generally used. What makes an element “essential”? By definition, an essential element is one that is required for life and whose absence results in death. ![]() Elements not known to be essential are shown in gray. Figure 1.26 The Essential Elements in the Periodic TableĮlements that are known to be essential for human life are shown in purple elements that are suggested to be essential are shown in green. ![]()
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