Trace element (also called micro- element ) is generally called a chemical element that occurs only in low concentrations or in traces; if the concentration is extremely low, it is also referred to as ultra-trace element .
The abundances of chemical elements differ considerably, if you consider their occurrence in the solar system , in planet earth , in rocks of the earth's crust , in the water of oceans or, for example, in the human body . Within the respective frequency distribution, the common elements are separated from the rare trace elements as quantity elements.
While in geochemistry the proportions and accompanying elements of rocks and minerals in concentrations below 0.1% or 1000 ppm are referred to as trace elements , analytical chemistry usually prefers a threshold value of 100 ppm or 100 µg / g (= 100 mg / kg) or 0.01%. The more narrowly defined biological term must be distinguished from this:
In biology, chemical elements are called essential trace elements which are ( essentially ) necessary for a living being - colloquially mostly related to humans - and which occur in the organism in mass proportions of less than 50 mg / kg. At concentrations of less than 1 µg / kg, the term ultra-trace elements is sometimes used. Microelements belong to the group of micronutrients .
Trace elements essential for humans
Too little or even the lack of essential trace elements causes deficiency diseases in living beings . Such deficiency symptoms - such as anemia due to iron deficiency or an enlargement or hypofunction of the thyroid gland due to iodine deficiency - make the indispensability (essentiality) of an element obvious. On the other hand, trace elements - like any substance above a certain dose - can also have detrimental consequences in excessive amounts.
Trace elements are usually ingested when eating and drinking with food that contains them in trace amounts. With reduced intake, increased excretion or increased need, the body may be insufficiently supplied with trace elements. Possible reasons for this are
- Eating habits - e.g. B. low selection, one-sided preference, special forms of preparation or separation processes of food
- Regional conditions - for example very little occurrence in arable land or drinking water
- increased loss, for example from diarrhea or profuse sweating
- changed conditions for uptake, excretion and need in different metabolic diseases
Medically, iron (Fe) is assigned to trace elements because of its mode of action; humans contain an average of around 60 mg / kg.
Fluorine (F), on the other hand, is not one of the essential trace elements, but fluoride (F - ) has a caries- preventing effect. The Federal Institute for Risk Assessment (2006) recommends an average total amount of 3.1 mg per day as an appropriate fluoride intake for adults, including for pregnant and nursing mothers. A similar value of 0.05 mg / kg body weight for daily intake is recommended by the EU Commission's Scientific Advisory Committee on Food Safety (2013). The daily maximum recommended amount ( Tolerable Upper Intake Level , UL) is 7 mg for adults or 0.1 mg / kg body weight. Excessive fluoride intake can lead to fluorosis of the teeth ( dental fluorosis ) and the skeleton ( osseous fluorosis ).
For a number of trace elements in very low concentrations ( boron , bromine , cadmium , lead , lithium ) it is still unclear whether they only occur as an accidental (“random”) component in humans or whether they have any physiological function.
Collection of trace elements
Trace elements (or ultra-trace elements) essential for humans are:
- Chromium (Cr)
- Cobalt (Co)
- Iron (Fe)
- Iodine (I), absorption as iodide (I - )
- Copper (Cu)
- Manganese (Mn)
- Molybdenum (Mo)
- Selenium (Se)
- Silicon (Si)
- Zinc (Zn)
Trace elements may be essential for humans
|element||Good source||Importance to the body||Recommended intake per day|
|chrome||Meat, whole grain products, vegetable oils, beer (in Western Europe steel (processing, cookware) is the most important source)||unexplained / controversial, glucose metabolism||20–100 µg (estimate), 30–140 µg|
|Cobalt||Animal products of all kinds||Part of cobalamin (vitamin B 12 ), only essential as such||0.2 µg, no recommendation|
|iron||Pork liver, sauerkraut (The spinach recommended earlier has a high iron content, but because of the oxalates and tannins it also contains, this iron can only be absorbed to a small extent. Iron from plant-based foods is generally poorly absorbed due to the simultaneous intake of reducing food components, especially ascorbic acid (Vitamin C) , the absorption rate of vegetable iron can be increased up to seven times.)||Part of many enzymes and z. B. of hemoglobin||10-15 mg|
|Iodine||Marine fish, crustaceans, edible algae||Part of the thyroid hormones||200 µg|
|copper||Whole grains, nuts, cocoa, some green vegetables, ruminant entrails, fish and shellfish||Part of numerous redox enzymes||1-1.5 mg|
|manganese||Black tea, nuts, whole grains and green leafy vegetables||Activator and component of numerous enzymes → antioxidative metabolism, cartilage and bone synthesis , gluconeogenesis||1 mg, 2-5 mg|
|molybdenum||Omnipresent (ubiquitous)||Part of the universal molybdenum cofactor||50-100 µg|
|nickel||Part of urease , methyl coenzyme M reductase , some hydrogenases , carbon monoxide dehydrogenase||25-30 µg|
|selenium||Animal proteins from farm animals fed with selenium (Central Europe) → eggs, meat||Part of 30–50 selenoproteins such as glutathione peroxidase||1.5 µg / kg, 30-70 µg|
|Silicon||Millet, beer||essential component of the mucopolysaccharides in epithelia and connective tissue About 1.4 g in the human body.||30 mg|
|Vanadium||Legumes, nuts, seafood||various effects in the body, such as stimulation of glycolysis in the liver , inhibition of gluconeogenesis - essentiality unexplained||<10 µg|
|zinc||Animal foods, especially cheese, offal, muscle meat, some types of fish and especially shellfish||Zinc-dependent enzymes are involved in almost all life processes, e.g. B. synthesis of collagen , thymulin , testosterone or breakdown of alcohol by alcohol dehydrogenase involved||12-15 mg, 7-10 mg|
Position in the periodic table of chemical elements:
|N / A||Mg||Al||Si||P||S.||Cl||Ar|
|The four basic organic elements||Set elements||essential trace elements||probably essential trace elements|
Biological importance for humans
Iron is required by the body, among other things, for building important proteins and for regenerating red blood cells and muscles. Iron deficiency is the most common cause of anemia . This manifests itself initially through rapid exhaustion during physical activity and, in the manifest stage, also through pale, rough skin and brittle fingernails and hair.
Iron is available in sufficient form in many foods. The actual iron content of a food is of secondary importance for iron absorption. What is more important is which foods are combined. This is due to the fact that a number of food components strongly promote or inhibit iron absorption. A combination with vitamin C is particularly beneficial for the absorption of iron from plant sources. On the other hand, substances in coffee, black tea and spinach , for example, formerly wrongly recommended as a good source of iron, inhibit iron absorption particularly strongly.
|Food source||Iron content|
|Chicken egg yolk|
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