Copper by R.Borgacci

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What is copper?

Copper ("copper" in English) is a chemical element with the symbol Cu (from the Latin "cuprum") and atomic number 29.

Like iron and zinc, copper is also a metal-micronutrient essential to all higher living organisms - the same is not true for microorganisms. Implicit above all in oxidation-reduction reactions and in protein synthesis, for example for the production of certain enzymes, in the human organism it plays a fundamental role for the constitution of the biological respiratory cytochrome C oxidase catalyst - also known as complex IV, EC 1.9.3.1. An adult's body contains 1.4 - 2.1 milligrams of copper per kilogram of weight and the richest tissues are: hepatic, muscular and bone parenchyma.

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In molluscs and crustaceans, copper is a constituent of the hemocyanin of blood pigment; in these organisms it has the same function as iron for man's hemoglobin and many other vertebrates.

The nutritional requirement of copper for our body is objectively moderate and it is not a nutritional factor which is normally easy to get into deficit; its deficiency is more likely when associated with general malnutrition pictures. Among the richest foods in copper we mention: offal, molluscs, crustaceans, oilseeds and starchy seed germs. The absorption - intestinal - is affected, as well as by its presence in the food, also by the general composition of the meals - for example for the possible presence of large quantities of iron, zinc or anti-nutritional chelating agents. Its metabolism can be affected by hereditary diseases even of serious entity.

Biological Role

Biological role of copper

The biological role of copper began with the appearance of oxygen in the earth's atmosphere. Copper is an essential trace element both in the animal and vegetable kingdoms, but not in that of bacteria and viruses.

In nature, copper is mainly proteins, such as enzymes and transporters, which play different roles in catalysis and transfer of biological or oxygen electrons - processes that exploit the easy interconversion of copper types I and II - Cu (I) and Cu (II) .

Copper is essential in the aerobic respiration of all eukaryotic cells. In the mitochondria, it is found in the cytochrome C oxidase enzyme, the last protein in oxidative phosphorylation that binds O2 between a copper and an iron ion, transferring 8 electrons to the O2 molecule and thus reducing it, for the consequent link with hydrogen, with two molecules of water.

Copper is also found in many superoxide dismutase enzymes, proteins that catalyze the decomposition of superoxides by converting them, by dismutation, into oxygen and hydrogen peroxide.

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The reaction of the superoxide dismutase enzyme is as follows:

Cu2 + -SOD + O2- → Cu + -SOD + O2 (copper reduction, superoxide oxidation)

Cu + -SOD + O2- + 2H + → Cu2 + -SOD + H2O2 (copper oxidation, superoxide reduction)

The hemocyanin protein is the oxygen carrier in most molluscs and some arthropods, such as the prehistoric crustacean Limulus polyphemus . Since hemocyanin is blue, these organisms have blood of the same color and not red - instead typical of our iron-based hemoglobin.

Several copper proteins, such as "blue copper proteins", do not interact directly with the substrates and are not enzymes . Instead, these polypeptides transmit electrons through the process called " electron transfer ".

Metabolism

Copper metabolism in the human body

Copper is absorbed into the intestine and into the bloodstream, where it binds to albumin and is transported to the liver. After hepatic metabolism, it is distributed to other tissues mainly thanks to the ceruloplasmin protein. The latter also carries copper secreted in the breast milk of mammals and is particularly well absorbed. For more information, see: Ceruloplasmin.

Normally copper flows in an enterohepatic circulation - a "recycling" of about 5 mg / day - while only 1 mg / day is absorbed with the diet and expelled. If necessary, the organism is able to eliminate the excess through the bile, which will therefore not be significantly reabsorbed by the intestine.

The human body contains copper in an amount of about 1.4 - 2.1 mg / kg of weight - contained mainly in the liver, muscles and bones.

Diet

Copper source source IOM

In 2001, the "US Institute of Medicine" (IOM) updated the estimated average requirements (EAR) and recommended dietary allowances (recommended dietary allowances - RDA) for copper. When insufficient information is available to establish EAR and RDA, for example with regard to newborns, a defined estimate of adequate intake (adequate intake - AI) is used.

Adequate intake of copper

The AI ​​for copper up to one year of age correspond to:

• 200 μg / day of copper for males and females 0-6 months
• 220 μg / day of copper for males and females of 7-12 months.

Recommended dietary ration of copper

The RDAs for copper are:

• 340 μg / day of copper for males and females 1-3 years old
• 440 μg / day of copper for males and females of 4-8 years
• 700 μg / day of copper for males and females 9-13 years old
• 890 μg / day of copper for males and females aged 14-18
• 900 μg / day of copper for males and females aged 19 or older
• 1000 μg / day of copper for pregnant females of 14-50 years
• 1300 μg / day of copper for lactating females aged 14-50.

Tolerable upper intake levels of copper

As far as the safety level is concerned, with sufficient data to establish them, the IOM also imposes tolerable higher levels of tolerance (tolerable upper intake levels - UL). In the case of copper, the UL is set at 10 mg / day.

Note : collectively the EARs, the RDAs, the IAs and the ULs are indicated as dietary reference references (Dietary Reference Intakes - DRI).

EFSA source of copper

The European Food Safety Authority (EFSA) refers to the collective series of information as Dietary Reference Values ​​(DRV), with Population Reference Intake (PRI) instead of the RDA and Average Requirement (AR) instead of EAR. For women and men aged 18 and older, IAs are set at 1.3 and 1.6 mg / day respectively. The AI ​​for pregnancy and lactation are 1.5 mg / day. For children aged 1-17 years, AI increases with age from 0.7 to 1.3 mg / day - they are therefore higher than US RDAs. EFSA has set its UL at 5 mg / day, which is half the value of the United States.

Copper on the food label in the USA

For the purposes of labeling food supplements and dietary foods in the United States, the amount of copper in a portion is expressed as a percentage of the daily value (% day value -% DV).

100% of the DV was 2.0 mg, but from May 27th 2016 it was revised to 0.9 mg to bring it in line with the RDA.

Food

Foods rich in copper

Among the foods rich in copper there are both foods of animal and vegetable origin. Typical examples are: liver as a food, kidney or kidney as food, oysters, crabs, lobster, cocoa, walnuts, pecans, peanuts, sunflower seeds and its oil, corn germ and its oil, wheat or rye bran, beans, lentils, cocoa, chocolate etc.

Secondary sources are: meat, especially lamb, and some fruits such as lemons, apples, papaya, coconut, etc., mushrooms and brewer's yeast.

The topic is better developed on the page: Copper in Foods.

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Symptoms of the nutritional deficiency of copper

Due to its role in facilitating iron absorption, the nutritional deficiency of copper can cause symptoms similar to iron deficiency anemia, with the possibility of:

• neutropenia
• bone anomalies
• hypopigmentation
• reduced growth
• increased incidence of infections
• osteoporosis
• hyperthyroidism
• abnormalities in glucose and cholesterol metabolism.

Diagnosis of nutritional deficiency of copper

The state of severe copper deficiency can be found by testing the plasma levels of the mineral - or serum copper - of ceruloplasmin and superoxide dismutase in red blood cells. Note : these parameters are not sensitive to the marginal lack of copper in the diet. As an alternative it is possible to resort to the analysis of the activity of the cytochrome c oxidase enzyme in leukocytes and platelets, but it is not clear whether the results of this test give actually repeatable results.

Toxicity

Food copper toxicity

Observing some suicide attempts, it was found that excessive amounts of copper - in the form of salts - can induce acute toxicity, probably due to the redox and the generation of reactive oxygen species harmful to DNA.

In various farm animals, such as the rabbit, the toxic amount of copper salts is equivalent to 30 mg / kg. To ensure satisfactory growth, at least 3 ppm / day is needed, and 100, 200, 500 ppm, can favorably affect anabolic metabolism and therefore the growth rate of the animals.

In humans, as a rule, cases of chronic toxicity are unlikely to occur, thanks to the transport systems that regulate the absorption and excretion of the mineral.

However, autosomal recessive mutations in copper transport proteins can disable these systems, leading to Wilson's copper-accumulating disease - also in the eyes, typically referred to as Kayser-Fleischer rings - and liver cirrhosis in people who inherited two defective genes. For more information on drugs and Wilson's disease read also the dedicated article.

Excessive levels of copper have also been linked to worsening symptoms of Alzheimer's disease.

Exposure to copper toxicity

In the United States, the Occupational Safety and Health Administration (OSHA) has designated an allowed exposure limit (PEL) for copper dusts and related fumes in the workplace of 1 mg / m3 - time-weighted average (TWA). The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 1 mg / m3 TWA. The value "immediately dangerous for life and health" (IDLH) is 100 mg / m3.

Copper is also a constituent of the tobacco plant, which rapidly absorbs metals from the surrounding soil to accumulate in the leaves. With the smoking, in addition to that of the toxic constituents of the combustion - of which the harmfulness is widely documented - a potentially harmful role of these elements is also suspected.

Popular Medicine

Copper in folk medicine

Recently some compression garments containing braided copper have entered the market. Such clothing would have promiscuous therapeutic indications, combining the compression function suggested by conventional medicine for the treatment of some specific disorders to the "energy potential" of the material instead established by folk medicine.

Material

Properties and characteristics of copper as a material

As a material it boasts properties of softness, malleability, extreme ductility and high thermal and electrical conductivity. The surface of pure copper, just exposed - so not yet oxidized - has a red-orange color. Copper is used as a conductor of heat and electricity, as a construction material and as a component of various alloys, such as silver used in jewelery, cupronickel used to manufacture hardware and marine coins and constantan used for strain gauges and thermocouples useful for temperature measurement.

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Copper is one of the few metals found in nature in the already usable form - native metal. This allowed its use by man as early as 8000 BC It was the first metal to be melted by its mineral (5000 BC), the first to be printed (4000 BC) and the first to constitute an intentional alloy with another metal, the tin, to create bronze (3500 BC).

In the past - already in Roman times - copper was extensively extracted and used for various applications. The compounds most frequently found from the finds are copper salts (copper II or Cu II), which often give a blue or green color to the type minerals: azurite, malachite and turquoise - widely used as pigments. Copper used in buildings, usually as a coating, oxidizes to form a greenish patina. Copper is also sometimes used in decorative art, both in its elementary metal form and in other compounds. Various copper materials are used as bacteriostatic agents, fungicides and wood preservatives.

Antibiofouling - anti-accumulator

Copper is a biostatic compound, ie it does not allow the growth of bacteria and many other life forms.

It is therefore a very effective anti-fouling and therefore, in the past, has found abundant use in the nautical sector - first in purity, then in muntz alloy (40% zinc) or copper paint. Copper was necessary to structure and cover components and surfaces located below the waterline - the boat's living craft - on which algae, mussels, gramostini (dog's teeth), limpets etc. are usually developed.

Thanks to the property of "anti-bioaccumulator", copper alloys have then become fundamental materials in cross-linking in aquaculture; they also have excellent antimicrobial, structural and corrosion resistance properties.

Antimicrobial copper

The antibacterial copper alloy contact surfaces have natural properties that destroy a wide range of microorganisms - for example E. coli O157: H7, methicillin- resistant Staphylococcus aureus (MRSA), Staphylococcus, Clostridium difficile, dell virus ' influenza A, adenovirus and various fungi. Regularly cleaned, hundreds of copper alloys have been shown to kill over 99.9% of pathological bacteria in just two hours. The "United States Environmental Protection Agency" (EPA) has approved the registration of these copper alloys as "antimicrobial material with public health benefits", allowing manufacturers to claim the benefits. In addition, the EPA has approved a long list of copper antimicrobial products obtained from these alloys, such as handrails, railings, sinks, faucets, door knobs, toilet hardware, computer keyboards, equipment for wellness centers and shopping trolley handles. Copper handles are used in hospitals to reduce the transfer of pathogens. The bacterium of "Legionnaire's disease" or "legionellosis" ( Legionella pneumophila ) is suppressed by the use of copper tubes in hydraulic systems. Antimicrobial copper alloy products are installed in healthcare facilities in the following countries: United Kingdom, Ireland, Japan, Korea, France, Denmark and Brazil, as well as in the metro transportation system in Santiago, Chile, where - between 2011 and 2014 - copper and zinc handrails will be installed in around 30 stations.

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Chromobacterium violaceum and Pseudomonas fluorescens can mobilize solid copper as a cyanide compound.

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