Calcium is a chemical element, Ca symbol and atomic number 20.

Calcium is an alkaline earth metal grey and soft. It is used as a reducing agent in the extraction of thorium, zirconium and uranium. This element not found never to the state of pure body in nature is the fifth most abundant element of the earth's crust and is essential for organic matter.

Features significant
Calcium can be produced by electrolysis fluoride calcium but more commonly by reducing vacuum Lime (CaO) with aluminum powder.

It burns with a yellow flame-red; exposed to air dry it forms a protective coating white oxide and nitride. It reacts violently with water it displaces hydrogen and then form of calcium hydroxide Ca (OH) 2.

Applications physical calcium metal

* Agent reducer in the extraction of other metals such as uranium zirconium and thorium;
* Désoxydant, désulfurant or décarburant for different alloys ferrous and non-ferrous;
* Used, sometimes in association with magnesium, to eliminate bismuth lead (débismuthage);
* Agent alloy used in the production of alloys of aluminum, beryllium, copper, lead and magnesium.

Calcium compounds

* Calcium Carbonate CaCO3, widespread in nature, because it is the basic component of limestone, but by calcining limestone that gives the quicklime, see also: calcite, aragonite
* CaO calcium oxide (lime) and calcium hydroxide Ca (OH) 2 (slaked lime)
* Aluminate calcium (Al2O3, 3CaO): One of the components of clinker, and used for the manufacture of mortars refractory
* Calcium Carbide CaC2 (commonly known as carbide and its hydrolysis product of acetylene)
* Halides calcium:
o Calcium chloride CaCl2 sometimes used as road salt to replace sodium chloride
o calcium fluoride CaF2 (fluorine)
o iodide calcium CaI2
o calcium bromide CaBr2
* Nitride calcium Ca3N2
* Calcium peroxide CaO2
* Phosphide calcium Ca3P2 (its hydrolysis generates phosphine PH3)
* Calcium sulfide CaS
* Calcium phosphate Ca3 (PO4) 2
* Calcium-Silico (calcium-silicon alloy) used in steel industry
* Calcium hypochlorite Ca (ClO) 2
* Alun double aluminium sulphate and potassium hydrate and is used in dyeing (to fix the dyes), for the conservation of skins, bonding of pulp, the hardening plaster.

The calcium in the diet
Calcium is by far the most abundant mineral in the body. It is mostly stored in the bones, which is an integral part. It contributes to the formation of the latter, as well as teeth, and maintaining their health. Calcium also plays a vital role in blood clotting, maintaining blood pressure and contraction of muscles, including the heart.

Importance physiological
Calcium is an important component of a healthy diet. Contrary to popular belief, these are not the dairy products that represent the best source of calcium, as the proportion calcium / phosphorus is not good. The milk contains too phosphorus, which can lead to calcification insufficient. The body needs magnesium, silicon, vitamins A, C and D, protein and phosphorus in order to assimilate.

Calcium is involved in the formation of bones and teeth, its deficit will affect them (osteoporosis, growth problems). His excesses leads to the appearance of kidney stones. Besides, it intervenes in the cellular exchanges and is, therefore, vital. His blood (calcium) is highly regulated to prevent fatal variations in the body. The hormones involved in this regulation are the parathyroid hormone and calcitonin, although the role "hormonal" calcitonin be discussed given that its growth does not change on the phospho calcium metabolism. It would be more accurate to consider the parathyroid and calcitriol (derivative of vitamin D) as the two main hormones phospho calcium metabolism. See also calcium metabolism. Calcium is also used to regulate body pH, it is released bones where acidification of internal environment caused by consumption of the product acid (protein, milk ...) and low consumption of plants that have an effect alkanisant .

The risk of colon cancer appears diminished by a diet rich in calcium. The majority of epidemiological studies indicate that people whose diet contains more calcium are less frequently colorectal cancer. More than 25 scientific publications show that calcium reduces colon cancer in rodents. Finally, three controlled clinical trials show that taking a supplement of calcium carbonate (1-2 g / d) reduces the recurrence of polyps by 15 to 30% in volunteers: It seems that calcium prevents colorectal cancer.

Presence of calcium in our food
Calcium is present in many foods consumed.

Dairy products are the main source of dietary calcium (more than two-thirds). Calcium is present in a form that is a good intestinal absorption (about 30%) and that do not urinary excretion, allowing the final good bioavailability.

Other foods contain calcium: tap water, almonds, parsley, figs, watercress, soybeans, cocoa, dandelion, egg yolk, sesame seeds, spinach, fish, ... (see detailed article). Calcium of plant origin, however, is most often less absorbed because it is largely insolubilisé irreversibly in the form of phytates (soybean) or oxalates (spinach, cocoa). Thus the absorbability of calcium spinach would not exceed 5%.

To assess the bioavailability real, we must also take into account the dietary factors that influence the urinary loss of calcium absorbed. Thus the simultaneous absorption of phosphorus decreases urinary excretion of calcium. In contrast, components "acid" of the regime, such as sulfates (especially in mineral waters calcium sulphate), increase calciurie.

Finally, the setting of calcium absorbed from the bone (preventing osteoporosis) depends on many other factors, in particular hormone (see above).

Calcium as a medicinal product
The absorption of calcium in the form of pills can increase its daily intake if he is not optimal. It is sometimes associated with taking vitamin D. It seems to be effective in the preventive treatment of osteoporosis in the elderly, reducing the rate of fractures as well as the indices of bone demineralization. The side effect is most noted constipation. However, this supplementation may be associated with an increased risk of cardiovascular disease, although this figure remains discussed.

The lime was already prepared by the Romans from the first century, but it was not until 1808 that calcium was discovered. Upon learning that Jöns Jacob Berzelius Martin and Magnus Pontin had prepared a mixture of calcium by electrolysis of lime in mercury, Sir Humphry Davy was able to isolate the metal impure.

Calcium is the fifth most abundant element in the earth's crust (he shaped over 3%) and an essential element for the formation of bones, teeth and shells. Calcium also plays a very important role in cellular physiology.

The recommended daily value is 700 mg per day for adults.

Read also Osteoporosis