Calcium

From Wikipedia, the free encyclopedia - View original article

Calcium
20Ca
Hydrogen (diatomic nonmetal)
Helium (noble gas)
Lithium (alkali metal)
Beryllium (alkaline earth metal)
Boron (metalloid)
Carbon (polyatomic nonmetal)
Nitrogen (diatomic nonmetal)
Oxygen (diatomic nonmetal)
Fluorine (diatomic nonmetal)
Neon (noble gas)
Sodium (alkali metal)
Magnesium (alkaline earth metal)
Aluminium (other metals)
Silicon (metalloid)
Phosphorus (polyatomic nonmetal)
Sulfur (polyatomic nonmetal)
Chlorine (diatomic nonmetal)
Argon (noble gas)
Potassium (alkali metal)
Calcium (alkaline earth metal)
Scandium (transition metal)
Titanium (transition metal)
Vanadium (transition metal)
Chromium (transition metal)
Manganese (transition metal)
Iron (transition metal)
Cobalt (transition metal)
Nickel (transition metal)
Copper (transition metal)
Zinc (transition metal)
Gallium (other metals)
Germanium (metalloid)
Arsenic (metalloid)
Selenium (polyatomic nonmetal)
Bromine (diatomic nonmetal)
Krypton (noble gas)
Rubidium (alkali metal)
Strontium (alkaline earth metal)
Yttrium (transition metal)
Zirconium (transition metal)
Niobium (transition metal)
Molybdenum (transition metal)
Technetium (transition metal)
Ruthenium (transition metal)
Rhodium (transition metal)
Palladium (transition metal)
Silver (transition metal)
Cadmium (transition metal)
Indium (other metals)
Tin (other metals)
Antimony (metalloid)
Tellurium (metalloid)
Iodine (diatomic nonmetal)
Xenon (noble gas)
Caesium (alkali metal)
Barium (alkaline earth metal)
Lanthanum (lanthanide)
Cerium (lanthanide)
Praseodymium (lanthanide)
Neodymium (lanthanide)
Promethium (lanthanide)
Samarium (lanthanide)
Europium (lanthanide)
Gadolinium (lanthanide)
Terbium (lanthanide)
Dysprosium (lanthanide)
Holmium (lanthanide)
Erbium (lanthanide)
Thulium (lanthanide)
Ytterbium (lanthanide)
Lutetium (lanthanide)
Hafnium (transition metal)
Tantalum (transition metal)
Tungsten (transition metal)
Rhenium (transition metal)
Osmium (transition metal)
Iridium (transition metal)
Platinum (transition metal)
Gold (transition metal)
Mercury (transition metal)
Thallium (other metals)
Lead (other metals)
Bismuth (other metals)
Polonium (other metals)
Astatine (metalloid)
Radon (noble gas)
Francium (alkali metal)
Radium (alkaline earth metal)
Actinium (actinide)
Thorium (actinide)
Protactinium (actinide)
Uranium (actinide)
Neptunium (actinide)
Plutonium (actinide)
Americium (actinide)
Curium (actinide)
Berkelium (actinide)
Californium (actinide)
Einsteinium (actinide)
Fermium (actinide)
Mendelevium (actinide)
Nobelium (actinide)
Lawrencium (actinide)
Rutherfordium (transition metal)
Dubnium (transition metal)
Seaborgium (transition metal)
Bohrium (transition metal)
Hassium (transition metal)
Meitnerium (unknown chemical properties)
Darmstadtium (unknown chemical properties)
Roentgenium (unknown chemical properties)
Copernicium (transition metal)
Ununtrium (unknown chemical properties)
Flerovium (unknown chemical properties)
Ununpentium (unknown chemical properties)
Livermorium (unknown chemical properties)
Ununseptium (unknown chemical properties)
Ununoctium (unknown chemical properties)
Mg

Ca

Sr
potassiumcalciumscandium
Calcium in the periodic table
Appearance
dull gray, silver


Spectral lines of calcium
General properties
Name, symbol, numbercalcium, Ca, 20
Pronunciation/ˈkælsiəm/ KAL-see-əm
Element categoryalkaline earth metal
Group, period, block2 (alkaline earth metals), 4, s
Standard atomic weight40.078(4)
Electron configuration[Ar] 4s2
2, 8, 8, 2
Physical properties
Phasesolid
Density (near r.t.)1.55 g·cm−3
Liquid density at m.p.1.378 g·cm−3
Melting point1115 K, 842 °C, 1548 °F
Boiling point1757 K, 1484 °C, 2703 °F
Heat of fusion8.54 kJ·mol−1
Heat of vaporization154.7 kJ·mol−1
Molar heat capacity25.929 J·mol−1·K−1
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)8649561071122714431755
Atomic properties
Oxidation states+2, +1[1]
(strongly basic oxide)
Electronegativity1.00 (Pauling scale)
Ionization energies
(more)
1st: 589.8 kJ·mol−1
2nd: 1145.4 kJ·mol−1
3rd: 4912.4 kJ·mol−1
Atomic radius197 pm
Covalent radius176±10 pm
Van der Waals radius231 pm
Miscellanea
Crystal structureface-centered cubic
Calcium has a face-centered cubic crystal structure
Magnetic orderingdiamagnetic
Electrical resistivity(20 °C) 33.6 nΩ·m
Thermal conductivity201 W·m−1·K−1
Thermal expansion(25 °C) 22.3 µm·m−1·K−1
Speed of sound (thin rod)(20 °C) 3810 m·s−1
Young's modulus20 GPa
Shear modulus7.4 GPa
Bulk modulus17 GPa
Poisson ratio0.31
Mohs hardness1.75
Brinell hardness167 MPa
CAS registry number7440-70-2
History
DiscoveryHumphry Davy (1808)
First isolationHumphry Davy (1808)
Most stable isotopes
Main article: Isotopes of calcium
isoNAhalf-lifeDMDE (MeV)DP
40Ca96.941%>5.9×1021 y(β+β+)0.19440Ar
41Catrace1.03×105 yε-41K
42Ca0.647%42Ca is stable with 22 neutrons
43Ca0.135%43Ca is stable with 23 neutrons
44Ca2.086%44Ca is stable with 24 neutrons
45Casyn162.7 dβ0.25845Sc
46Ca0.004%>2.8×1015 y(ββ)0.98846Ti
47Casyn4.536 dβ0.694, 1.9947Sc
γ1.297-
48Ca0.187%4.3×1019 yββ4.27448Ti
(β)0.005848Sc
Decay modes in parentheses are predicted, but have not yet been observed
· references
 
Jump to: navigation, search
This article is about the metallic element. For the place, see Calcium, New York.
Calcium
20Ca
Hydrogen (diatomic nonmetal)
Helium (noble gas)
Lithium (alkali metal)
Beryllium (alkaline earth metal)
Boron (metalloid)
Carbon (polyatomic nonmetal)
Nitrogen (diatomic nonmetal)
Oxygen (diatomic nonmetal)
Fluorine (diatomic nonmetal)
Neon (noble gas)
Sodium (alkali metal)
Magnesium (alkaline earth metal)
Aluminium (other metals)
Silicon (metalloid)
Phosphorus (polyatomic nonmetal)
Sulfur (polyatomic nonmetal)
Chlorine (diatomic nonmetal)
Argon (noble gas)
Potassium (alkali metal)
Calcium (alkaline earth metal)
Scandium (transition metal)
Titanium (transition metal)
Vanadium (transition metal)
Chromium (transition metal)
Manganese (transition metal)
Iron (transition metal)
Cobalt (transition metal)
Nickel (transition metal)
Copper (transition metal)
Zinc (transition metal)
Gallium (other metals)
Germanium (metalloid)
Arsenic (metalloid)
Selenium (polyatomic nonmetal)
Bromine (diatomic nonmetal)
Krypton (noble gas)
Rubidium (alkali metal)
Strontium (alkaline earth metal)
Yttrium (transition metal)
Zirconium (transition metal)
Niobium (transition metal)
Molybdenum (transition metal)
Technetium (transition metal)
Ruthenium (transition metal)
Rhodium (transition metal)
Palladium (transition metal)
Silver (transition metal)
Cadmium (transition metal)
Indium (other metals)
Tin (other metals)
Antimony (metalloid)
Tellurium (metalloid)
Iodine (diatomic nonmetal)
Xenon (noble gas)
Caesium (alkali metal)
Barium (alkaline earth metal)
Lanthanum (lanthanide)
Cerium (lanthanide)
Praseodymium (lanthanide)
Neodymium (lanthanide)
Promethium (lanthanide)
Samarium (lanthanide)
Europium (lanthanide)
Gadolinium (lanthanide)
Terbium (lanthanide)
Dysprosium (lanthanide)
Holmium (lanthanide)
Erbium (lanthanide)
Thulium (lanthanide)
Ytterbium (lanthanide)
Lutetium (lanthanide)
Hafnium (transition metal)
Tantalum (transition metal)
Tungsten (transition metal)
Rhenium (transition metal)
Osmium (transition metal)
Iridium (transition metal)
Platinum (transition metal)
Gold (transition metal)
Mercury (transition metal)
Thallium (other metals)
Lead (other metals)
Bismuth (other metals)
Polonium (other metals)
Astatine (metalloid)
Radon (noble gas)
Francium (alkali metal)
Radium (alkaline earth metal)
Actinium (actinide)
Thorium (actinide)
Protactinium (actinide)
Uranium (actinide)
Neptunium (actinide)
Plutonium (actinide)
Americium (actinide)
Curium (actinide)
Berkelium (actinide)
Californium (actinide)
Einsteinium (actinide)
Fermium (actinide)
Mendelevium (actinide)
Nobelium (actinide)
Lawrencium (actinide)
Rutherfordium (transition metal)
Dubnium (transition metal)
Seaborgium (transition metal)
Bohrium (transition metal)
Hassium (transition metal)
Meitnerium (unknown chemical properties)
Darmstadtium (unknown chemical properties)
Roentgenium (unknown chemical properties)
Copernicium (transition metal)
Ununtrium (unknown chemical properties)
Flerovium (unknown chemical properties)
Ununpentium (unknown chemical properties)
Livermorium (unknown chemical properties)
Ununseptium (unknown chemical properties)
Ununoctium (unknown chemical properties)
Mg

Ca

Sr
potassiumcalciumscandium
Calcium in the periodic table
Appearance
dull gray, silver


Spectral lines of calcium
General properties
Name, symbol, numbercalcium, Ca, 20
Pronunciation/ˈkælsiəm/ KAL-see-əm
Element categoryalkaline earth metal
Group, period, block2 (alkaline earth metals), 4, s
Standard atomic weight40.078(4)
Electron configuration[Ar] 4s2
2, 8, 8, 2
Physical properties
Phasesolid
Density (near r.t.)1.55 g·cm−3
Liquid density at m.p.1.378 g·cm−3
Melting point1115 K, 842 °C, 1548 °F
Boiling point1757 K, 1484 °C, 2703 °F
Heat of fusion8.54 kJ·mol−1
Heat of vaporization154.7 kJ·mol−1
Molar heat capacity25.929 J·mol−1·K−1
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)8649561071122714431755
Atomic properties
Oxidation states+2, +1[1]
(strongly basic oxide)
Electronegativity1.00 (Pauling scale)
Ionization energies
(more)
1st: 589.8 kJ·mol−1
2nd: 1145.4 kJ·mol−1
3rd: 4912.4 kJ·mol−1
Atomic radius197 pm
Covalent radius176±10 pm
Van der Waals radius231 pm
Miscellanea
Crystal structureface-centered cubic
Calcium has a face-centered cubic crystal structure
Magnetic orderingdiamagnetic
Electrical resistivity(20 °C) 33.6 nΩ·m
Thermal conductivity201 W·m−1·K−1
Thermal expansion(25 °C) 22.3 µm·m−1·K−1
Speed of sound (thin rod)(20 °C) 3810 m·s−1
Young's modulus20 GPa
Shear modulus7.4 GPa
Bulk modulus17 GPa
Poisson ratio0.31
Mohs hardness1.75
Brinell hardness167 MPa
CAS registry number7440-70-2
History
DiscoveryHumphry Davy (1808)
First isolationHumphry Davy (1808)
Most stable isotopes
Main article: Isotopes of calcium
isoNAhalf-lifeDMDE (MeV)DP
40Ca96.941%>5.9×1021 y(β+β+)0.19440Ar
41Catrace1.03×105 yε-41K
42Ca0.647%42Ca is stable with 22 neutrons
43Ca0.135%43Ca is stable with 23 neutrons
44Ca2.086%44Ca is stable with 24 neutrons
45Casyn162.7 dβ0.25845Sc
46Ca0.004%>2.8×1015 y(ββ)0.98846Ti
47Casyn4.536 dβ0.694, 1.9947Sc
γ1.297-
48Ca0.187%4.3×1019 yββ4.27448Ti
(β)0.005848Sc
Decay modes in parentheses are predicted, but have not yet been observed
· references

Calcium is the chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust. Calcium is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate.[2]

Calcium is essential for living organisms, in particular in cell physiology, where movement of the calcium ion Ca2+ into and out of the cytoplasm functions as a signal for many cellular processes. As a major material used in mineralization of bone, teeth and shells, calcium is the most abundant metal by mass in many animals.

Notable characteristics

Flame test. Brick-red color originates from calcium.

In chemical terms, calcium is reactive and soft for a metal (though harder than lead, it can be cut with a knife with difficulty). It is a silvery metallic element that must be extracted by electrolysis from a fused salt like calcium chloride.[3] Once produced, it rapidly forms a gray-white oxide and nitride coating when exposed to air. In bulk form (typically as chips or "turnings"), the metal is somewhat difficult to ignite, more so even than magnesium chips; but, when lit, the metal burns in air with a brilliant high-intensity orange-red light. Calcium metal reacts with water, generating hydrogen gas at a rate rapid enough to be noticeable, but not fast enough at room temperature to generate much heat, making it useful for generating hydrogen.[4] In powdered form, however, the reaction with water is extremely rapid, as the increased surface area of the powder accelerates the reaction with the water. Part of the reason for the slowness of the calcium–water reaction is a result of the metal being partly protected by insoluble white calcium hydroxide. In water solutions of acids, where this salt is soluble, calcium reacts vigorously.

With a density of 1.55 g/cm3, calcium is the lightest of the alkaline earth metals; magnesium (specific gravity 1.74) and beryllium (1.84) are denser though lighter in atomic mass. From strontium onward, the alkali earth metals become denser with increasing atomic mass.

Calcium has two allotropes.[5]

Calcium has a higher electrical resistivity than copper or aluminium, yet weight-for-weight, due to its much lower density, it is a rather better conductor than either. However, its use in terrestrial applications is usually limited by its high reactivity with air.

Calcium salts are colorless from any contribution of the calcium, and ionic solutions of calcium (Ca2+) are colorless as well. As with magnesium salts and other alkaline earth metal salts, calcium salts are often quite soluble in water. Notable exceptions include calcium hydroxide, calcium sulfate (unusual for sulfate salts), calcium carbonate and tricalcium phosphate. With the exception of calcium sulfate, even the insoluble calcium salts listed are in general more soluble than the transition metal counterparts. When in solution, the calcium ion varies remarkably to the human taste, being reported as mildly salty, sour, "mineral-like" or even "soothing." It is apparent that many animals can taste, or develop a taste, for calcium, and use this sense to detect the mineral in salt licks or other sources.[6] In human nutrition, soluble calcium salts may be added to tart juices without much effect to the average palate.

Calcium is the fifth-most-abundant element by mass in the human body, where it is an important cellular ionic messenger with many functions. Calcium also serves as a structural element in bone. It is the relatively high-atomic-number calcium in the skeleton that causes bone to be radio-opaque. Of the human body's solid components after drying and burning of organics (as for example, after cremation), about a third of the total "mineral" mass remaining is the approximately one kilogram of calcium that composes the average skeleton (the remainder being mostly phosphorus and oxygen).

H and K lines

Visible spectra of many stars, including the Sun, exhibit strong absorption lines of singly ionized calcium. Prominent among these are the H-line at 3968.5 Å and the K line at 3933.7 Å of singly ionized calcium, or Ca II. When observing the Sun, or stars with low temperatures, the prominence of the H and K lines in the visible spectra can be an indication of strong magnetic activity in the chromosphere. Measurement of periodic variations of these active regions can also be used to deduce the rotation periods of these stars.[7]

Compounds

Calcium, combined with phosphate, forming hydroxylapatite, is the mineral portion of human and animal bones and teeth. The mineral portion of some corals can also be transformed into hydroxylapatite.

Calcium hydroxide (slaked lime) is used in many chemical refinery processes and is made by heating limestone at high temperature (above 825 °C) and then carefully adding water to it. When lime is mixed with sand, it hardens into a mortar and is turned into plaster by carbon dioxide uptake. Mixed with other compounds, lime forms an important part of Portland cement.

Calcium carbonate (CaCO3) is one of the common compounds of calcium. It is heated to form quicklime (CaO), which is then added to water (H2O). This forms another material known as slaked lime (Ca(OH)2), which is an inexpensive base material used throughout the chemical industry. Chalk, marble, and limestone are all forms of calcium carbonate.

When water percolates through limestone or other soluble carbonate rocks, it partially dissolves the rock and causes cave formation with their characteristic stalactites and stalagmites, and also forms hard water. Other important calcium compounds are calcium nitrate, calcium sulfide, calcium chloride, calcium carbide, calcium cyanamide and calcium hypochlorite.

A few calcium compounds where calcium is in the oxidation state +1 have also been investigated recently.[1]

Isotopes

Main article: Isotopes of calcium

Calcium has five stable isotopes (40Ca, 42Ca, 43Ca, 44Ca and 46Ca), plus one more isotope (48Ca) that has such a long half-life that for all practical purposes it can also be considered stable. The 20% range in relative mass among naturally occurring calcium isotopes is greater than for any other element except hydrogen and helium. Calcium also has a cosmogenic isotope, radioactive 41Ca, which has a half-life of 103,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column, where the cosmogenic neutron flux is still sufficiently strong. 41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies.

Ninety-seven percent of naturally occurring calcium is in the form of 40Ca. 40Ca is one of the daughter products of 40K decay, along with 40Ar. While K–Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K-Ca age dating.

The most abundant isotope, 40Ca, has a nucleus of 20 protons and 20 neutrons. This is the heaviest stable isotope of any element that has equal numbers of protons and neutrons. In supernova explosions, calcium is formed from the reaction of carbon with various numbers of alpha particles (helium nuclei), until the most common calcium isotope (containing 10 helium nuclei) has been synthesized.[citation needed]

Isotope fractionation

As with the isotopes of other elements, a variety of processes fractionate, or alter the relative abundance of, calcium isotopes.[8] The best studied of these processes is the mass-dependent fractionation[disambiguation needed] of calcium isotopes that accompanies the precipitation of calcium minerals, such as calcite, aragonite and apatite, from solution. Isotopically light calcium is preferentially incorporated into minerals, leaving the solution from which the mineral precipitated enriched in isotopically heavy calcium. At room temperature the magnitude of this fractionation is roughly 0.25‰ (0.025%) per atomic mass unit (AMU). Mass-dependent differences in calcium isotope composition conventionally are expressed the ratio of two isotopes (usually 44Ca/40Ca) in a sample compared to the same ratio in a standard reference material. 44Ca/40Ca varies by about 1% among common earth materials.[9]

Calcium isotope fractionation during mineral formation has led to several applications of calcium isotopes. In particular, the 1997 observation by Skulan and DePaolo[10] that calcium minerals are isotopically lighter than the solutions from which the minerals precipitate is the basis of analogous applications in medicine and in paleooceanography. In animals with skeletons mineralized with calcium the calcium isotopic composition of soft tissues reflects the relative rate of formation and dissolution of skeletal mineral. In humans changes in the calcium isotopic composition of urine have been shown to be related to changes in bone mineral balance. When the rate of bone formation exceeds the rate of bone resorption, soft tissue 44Ca/40Ca rises. Soft tissue 44Ca/40Ca falls when bone resorption exceeds bone formation. Because of this relationship, calcium isotopic measurements of urine or blood may be useful in the early detection of metabolic bone diseases like osteoporosis.[11]

A similar system exists in the ocean, where seawater 44Ca/40Ca tends to rise when the rate of removal of Ca2+ from seawater by mineral precipitation exceeds the input of new calcium into the ocean, and fall when calcium input exceeds mineral precipitation. It follows that rising 44Ca/40Ca corresponds to falling seawater Ca2+ concentration, and falling 44Ca/40Ca corresponds to rising seawater Ca2+ concentration. In 1997 Skulan and DePaolo presented the first evidence of change in seawater 44Ca/40Ca over geologic time, along with a theoretical explanation of these changes. More recent papers have confirmed this observation, demonstrating that seawater Ca2+ concentration is not constant, and that the ocean probably never is in “steady state” with respect to its calcium input and output.[12][13] This has important climatological implications, as the marine calcium cycle is closely tied to the carbon cycle (see below).

Geochemical cycling

Calcium provides an important link between tectonics, climate and the carbon cycle. In the simplest terms, uplift of mountains exposes Ca-bearing rocks to chemical weathering and releases Ca2+ into surface water. This Ca2+ eventually is transported to the ocean where it reacts with dissolved CO2 to form limestone. Some of this limestone settles to the sea floor where it is incorporated into new rocks. Dissolved CO2, along with carbonate and bicarbonate ions, are referred to as dissolved inorganic carbon (DIC).

Travertine terraces Pamukkale, Turkey

The actual reaction is more complicated and involves the bicarbonate ion (HCO3) that forms when CO2 reacts with water at seawater pH:

Ca2+
+ 2HCO
3
CaCO
3
(limestone) + CO
2
+ H
2
O

Note that at ocean pH most of the CO2 produced in this reaction is immediately converted back into HCO
3
. The reaction results in a net transport of one molecule of CO2 from the ocean/atmosphere into the lithosphere.[14]

The result is that each Ca2+ ion released by chemical weathering ultimately removes one CO2 molecule from the surficial system (atmosphere, ocean, soils and living organisms), storing it in carbonate rocks where it is likely to stay for hundreds of millions of years. The weathering of calcium from rocks thus scrubs CO2 from the ocean and atmosphere, exerting a strong long-term effect on climate.[15] Analogous cycles involving magnesium, and to a much smaller extent strontium and barium, have the same effect.

As the weathering of limestone (CaCO3) liberates equimolar amounts of Ca2+ and CO2, it has no net effect on the CO2 content of the atmosphere and ocean. The weathering of silicate rocks like granite, on the other hand, is a net CO2 sink because it produces abundant Ca2+ but very little CO2.

History

'Ain Ghazal figure

Lime as building material was used since prehistoric times going as far back as 7000 to 14000 BC.[16] Significant statues made from lime plaster date back into the 7 millennia BC were found in 'Ain Ghazal.[17] The first dated lime kiln dates back to 2500 BC and was found in Khafajah mesopotamia.[18][19] Calcium (from Latin calx, genitive calcis, meaning "lime")[20] was known as early as the first century when the Ancient Romans prepared lime as calcium oxide. Literature dating back to 975 AD notes that plaster of paris (calcium sulfate), is useful for setting broken bones. It was not isolated until 1808 in England when Sir Humphry Davy electrolyzed a mixture of lime and mercuric oxide.[21] Davy was trying to isolate calcium; when he heard that Swedish chemist Jöns Jakob Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury, he tried it himself. He worked with electrolysis throughout his life and also discovered/isolated sodium, potassium, magnesium, boron and barium. Calcium metal was not available in large scale until the beginning of the 20th century.

Occurrence

Calcium is not naturally found in its elemental state. Calcium occurs most commonly in sedimentary rocks in the minerals calcite, dolomite and gypsum. It also occurs in igneous and metamorphic rocks chiefly in the silicate minerals: plagioclases, amphiboles, pyroxenes and garnets.

Applications

Calcium is used[22]

Calcium compounds

Nutrition

Recommended adequate intake by the IOM for calcium:[24][25]
AgeCalcium (mg/day)
0–6 months200
7–12 months260
1–3 years700
4–8 years1000
9–18 years1300
19–50 years1000
51–70 years (male)1000
51–70 years (female)1200
71+ years1200

Calcium is an important component of a healthy diet and a mineral necessary for life. The National Osteoporosis Foundation says, "Calcium plays an important role in building stronger, denser bones early in life and keeping bones strong and healthy later in life." Approximately 99 percent of the body's calcium is stored in the bones and teeth.[26] The rest of the calcium in the body has other important uses, such as some exocytosis, especially neurotransmitter release, and muscle contraction. In the electrical conduction system of the heart, calcium replaces sodium as the mineral that depolarizes the cell, proliferating the action potential. In cardiac muscle, sodium influx commences an action potential, but during potassium efflux, the cardiac myocyte experiences calcium influx, prolonging the action potential and creating a plateau phase of dynamic equilibrium. Long-term calcium deficiency can lead to rickets and poor blood clotting and in case of a menopausal woman, it can lead to osteoporosis, in which the bone deteriorates and there is an increased risk of fractures. While a lifelong deficit can affect bone and tooth formation, over-retention can cause hypercalcemia (elevated levels of calcium in the blood), impaired kidney function and decreased absorption of other minerals.[27][28] Several sources suggest a correlation between high calcium intake (2000 mg per day, or twice the U.S. recommended daily allowance, equivalent to six or more glasses of milk per day) and prostate cancer.[29] High calcium intakes or high calcium absorption were previously thought to contribute to the development of kidney stones. However, a high calcium intake has been associated with a lower risk for kidney stones in more recent research.[30][31][32] Vitamin D is needed to absorb calcium.

Dairy products, such as milk and cheese, are a well-known source of calcium. Some individuals are allergic to dairy products and even more people, in particular those of non Indo-European descent, are lactose-intolerant, leaving them unable to consume non-fermented dairy products in quantities larger than about half a liter per serving. Others, such as vegans, avoid dairy products for ethical and health reasons.

Many good vegetable sources of calcium exist, including seaweeds such as kelp, wakame and hijiki; nuts and seeds like almonds, hazelnuts, sesame, and pistachio; blackstrap molasses; beans (especially soy beans); figs; quinoa; okra; rutabaga; broccoli; dandelion leaves; and kale. In addition, several foods and drinks, such as orange juice, soy milk, tofu, breakfast cereals, and breads are often fortified with calcium.[33]

Numerous vegetables, notably spinach, chard and rhubarb have a high calcium content, but they may also contain varying amounts of oxalic acid that binds calcium and reduces its absorption. The same problem may to a degree affect the absorption of calcium from amaranth, collard greens, and chicory greens. This process may also be related to the generation of calcium oxalate.

An overlooked source of calcium is eggshell, which can be ground into a powder and mixed into food or a glass of water.[34][35][36]

The calcium content of most foods can be found in the USDA National Nutrient Database.[37]

Dietary supplements

500 milligram calcium supplements made from calcium carbonate

Calcium supplements are used to prevent and to treat calcium deficiencies. Office of Dietary Supplements (National Institutes of Health) recommends that no more than 600 mg of supplement should be taken at a time because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases.[24] It is therefore recommended to spread doses throughout the day.[38] Recommended daily calcium intake for adults ranges from 1000 to 1300 mg.[38] Calcium supplements may have side effects such as bloating and constipation in some people. It is suggested that taking the supplements with food may aid in nullifying these side effects.[38]

Vitamin D is added to some calcium supplements. Proper vitamin D status is important because vitamin D is converted to a hormone in the body, which then induces the synthesis of intestinal proteins responsible for calcium absorption.[39]

Cardiovascular Impact

A study investigating the effects of personal calcium supplement use on cardiovascular risk in the Women’s Health Initiative Calcium/Vitamin D Supplementation Study (WHI CaD Study) found a modestly increased risk of cardiovascular events, particularly myocardial infarction in postmenopausal women. A broad recommendation of calcium/vitamin D supplements is therefore not warranted.[47] In contrast, the authors of a 2013 literature review concluded that the benefits of calcium supplementation, such as on bone health, appear to outweigh any risk calcium supplementation may theoretically pose to the cardiovascular health.[48]

Osteoporosis

Such studies often do not test calcium alone, but rather combinations of calcium and vitamin D. Randomized controlled trials found both positive[49] and negative[50][51][52][53] effects. The different results may be explained by doses of calcium and underlying rates of calcium supplementation in the control groups.[54]

Cancer

A meta-analysis[55] by the international Cochrane Collaboration of two randomized controlled trials[56][57] found that calcium "might contribute to a moderate degree to the prevention of adenomatous colonic polyps".

More recent studies were conflicting, and one that was positive for effect (Lappe, et al.) did control for a possible anti-carcinogenic effect of vitamin D, which was found to be an independent positive influence from calcium-alone on cancer risk (see second study below).[58]

Hazards and toxicity

Compared with other metals, the calcium ion and most calcium compounds have low toxicity. This is not surprising given the very high natural abundance of calcium compounds in the environment and in organisms. Calcium poses few serious environmental problems, with kidney stones the most common side-effect in clinical studies. Acute calcium poisoning is rare, and difficult to achieve unless calcium compounds are administered intravenously. For example, the oral median lethal dose (LD50) for rats for calcium carbonate and calcium chloride are 6.45[62] and 1.4 g/kg,[63] respectively.

Calcium metal is hazardous because of its sometimes-violent reactions with water and acids. Calcium metal is found in some drain cleaners, where it functions to generate heat and calcium hydroxide that saponifies the fats and liquefies the proteins (e.g., hair) that block drains. When swallowed calcium metal has the same effect on the mouth, esophagus and stomach, and can be fatal.[64]

Excessive consumption of calcium carbonate antacids/dietary supplements (such as Tums) over a period of weeks or months can cause milk-alkali syndrome, with symptoms ranging from hypercalcemia to potentially fatal renal failure. What constitutes “excessive” consumption is not well known and, it is presumed, varies a great deal from person to person. Persons consuming more than 10 grams/day of CaCO3 (=4 g Ca) are at risk of developing milk-alkali syndrome,[65] but the condition has been reported in at least one person consuming only 2.5 grams/day of CaCO3 (=1 g Ca), an amount usually considered moderate and safe.[66]

Oral calcium supplements diminish the absorption of thyroxine when taken within four to six hours of each other.[67] Thus, people taking both calcium and thyroxine run the risk of inadequate thyroid hormone replacement and thence hypothyroidism if they take them simultaneously or near-simultaneously.[68][unreliable medical source?]

Excessive[vague] calcium supplementation can be detrimental to cardiovascular health, especially in men.[69][70]

See also

References

  1. ^ a b Krieck, Sven; Görls, Helmar; Westerhausen, Matthias (2010). "Mechanistic Elucidation of the Formation of the Inverse Ca(I) Sandwich Complex [(thf)3Ca(μ-C6H3-1,3,5-Ph3)Ca(thf)3] and Stability of Aryl-Substituted Phenylcalcium Complexes". Journal of the American Chemical Society 132 (35): 100818110534020. doi:10.1021/ja105534w. PMID 20718434. 
  2. ^ Dickson, A. G. and Goyet, C. (1994). "5". Handbook of method for the analysis of the various parameters of the carbon dioxide system in sea water, version 2. ORNL/CDIAC-74. 
  3. ^ Pauling, Linus (1970). General Chemistry. Dover Publications. p. 627. ISBN 0-7167-0149-9. 
  4. ^ Theodore Gray. The Elements. Page 55
  5. ^ doi:10.1007/BF02873196
  6. ^ Tordoff, M. G. (2001). "Calcium: Taste, Intake, and Appetite". Physiological Reviews 81 (4): 1567–97. PMID 11581497. 
  7. ^ Staff (1995). "H-K Project". Mount Wilson Observatory. Retrieved 2006-08-10. 
  8. ^ Russell, WA; Papanastassiou, DA; Tombrello, TA (1978). "Ca isotope fractionation on the earth and other solar system materials". Geochim Cosmochim Acta 42 (8): 1075–90. Bibcode:1978GeCoA..42.1075R. doi:10.1016/0016-7037(78)90105-9. 
  9. ^ Skulan, J; Depaolo, DJ (1999). "Calcium isotope fractionation between soft and mineralized tissues as a monitor of calcium use in vertebrates". Proc Natl Acad Sci USA 96 (24): 13709–13. Bibcode:1999PNAS...9613709S. doi:10.1073/pnas.96.24.13709. PMC 24129. PMID 10570137. 
  10. ^ Skulan, J; Depaolo, DJ; Owens, TL (June 1997). "Biological control of calcium isotopic abundances in the global calcium cycle". Geochimica et Cosmochimica Acta 61 (12): 2505–10. Bibcode:1997GeCoA..61.2505S. doi:10.1016/S0016-7037(97)00047-1. 
  11. ^ Skulan, J; Bullen, T; Anbar, AD; Puzas, JE; Shackelford, L; Leblanc, A; Smith, SM (2007). "Natural calcium isotopic composition of urine as a marker of bone mineral balance". Clinical Chemistry 653 (6): 1155–1158. doi:10.1373/clinchem.2006.080143. PMID 17463176. 
  12. ^ Fantle, M; Depaolo, D (2007). "Ca isotopes in carbonate sediment and pore fluid from ODP Site 807A: The Ca2+(aq)–calcite equilibrium fractionation factor and calcite recrystallization rates in Pleistocene sediments". Geochim Cosmochim Acta 71 (10): 2524–2546. Bibcode:2007GeCoA..71.2524F. doi:10.1016/j.gca.2007.03.006. 
  13. ^ Griffith, Elizabeth M.; Paytan, Adina; Caldeira, Ken; Bullen, Thomas; Thomas, Ellen (2008). "A Dynamic marine calcium cycle during the past 28 million years". Science 322 (12): 1671–1674. Bibcode:2008Sci...322.1671G. doi:10.1126/science.1163614. PMID 19074345. 
  14. ^ Zeebe (2006). "Marine carbonate chemistry". National Council for Science and the Environment. Retrieved 2010-03-13. 
  15. ^ Berner, Robert (2003). "The long-term carbon cycle, fossil fuels and atmospheric composition". Nature 426 (6964): 323–326. Bibcode:2003Natur.426..323B. doi:10.1038/nature02131. PMID 14628061. 
  16. ^ Miller, M. Michael. "Commodity report:Lime". United States Geological Survey. Retrieved 2012-03-06. 
  17. ^ . JSTOR 41492234.  Missing or empty |title= (help)
  18. ^ Williams, Richard (2004). Lime Kilns and Lime Burning. p. 4. ISBN 978-0-7478-0596-0. 
  19. ^ Oates, J. A. H (2008-07-01). Lime and Limestone: Chemistry and Technology, Production and Uses. ISBN 978-3-527-61201-7. 
  20. ^ calx. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
  21. ^ Davy H (1808). "Electro-chemical researches on the decomposition of the earths; with observations on the metals obtained from the alkaline earths, and on the amalgam procured from ammonia". Philosophical Transactions of the Royal Society of London 98: 333–370. Bibcode:1808RSPT...98..333D. doi:10.1098/rstl.1808.0023. 
  22. ^ Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5. 
  23. ^ Newton, David E (2009-01-01). Food Chemistry. pp. 73–77. ISBN 9781438109756. 
  24. ^ a b "Dietary Supplement Fact Sheet: Calcium". Retrieved 2011-03-08. 
  25. ^ "Dietary Reference Intakes for Calcium and Vitamin D". November 2010. 
  26. ^ "Dietary Supplement Fact Sheet: Calcium". Office of Dietary Supplements, NIH. Retrieved 2011-03-31. 
  27. ^ Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine (1997). Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and fluoride. Washington DC: The National Academies Press. ISBN 0-309-06403-1. 
  28. ^ Committee to Review Dietary Reference Intakes for Vitamin D and Calcium; Institute of Medicine (2011). A. Catharine Ross, Christine L. Taylor, Ann L. Yaktine, Heather B. Del Valle, ed. Dietary Reference Intakes for Calcium and Vitamin D. ISBN 978-0-309-16394-1. 
  29. ^ Giovannucci E, Rimm EB, Wolk A, et al. (February 1998). "Calcium and fructose intake in relation to risk of prostate cancer". Cancer Research 58 (3): 442–7. PMID 9458087. 
  30. ^ Curhan, GC; Willett, WC; Rimm, EB; Stampfer, MJ (1993). "A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones" (PDF). The New England Journal of Medicine 328 (12): 833–8. doi:10.1056/NEJM199303253281203. PMID 8441427. 
  31. ^ Bihl G, Meyers A. (2001). "Recurrent renal stone disease-advances in pathogenesis and clinical management". Lancet 358 (9282): 651–656. doi:10.1016/S0140-6736(01)05782-8. PMID 11530173. 
  32. ^ Hall WD, Pettinger M, Oberman A (2001). "Risk factors for kidney stones in older women in the Southern United States". Am J Med Sci 322 (1): 12–18. doi:10.1097/00000441-200107000-00003. PMID 11465241. 
  33. ^ Calcium in Diet, Medline Plus, US National Institutes of Health. Section "Other sources of calcium". Accessed 2014-02-12
  34. ^ Schaafsma, Anne and Beelen, Gerard M (1999). "Eggshell powder, a comparable or better source of calcium than purified calcium carbonate: piglet studies". Journal of the Science of Food and Agriculture 79 (12): 1596–1600. doi:10.1002/(SICI)1097-0010(199909)79:12<1596::AID-JSFA406>3.0.CO;2-A. 
  35. ^ Schaafsma A, van Doormaal JJ, Muskiet FA, Hofstede GJ, Pakan I, van der Veer E (2002). "Positive effects of a chicken eggshell powder-enriched vitamin-mineral supplement on femoral neck bone mineral density in healthy late post-menopausal Dutch women". Br. J. Nutr. 87 (3): 267–75. doi:10.1079/BJNBJN2001515. PMID 12064336. 
  36. ^ Rovenský J, Stancíková M, Masaryk P, Svík K, Istok R (2003). "Eggshell calcium in the prevention and treatment of osteoporosis". Int J Clin Pharmacol Res 23 (2–3): 83–92. PMID 15018022. 
  37. ^ "USDA National Nutrient Database". 
  38. ^ a b c "Dietary Supplement Fact Sheet: Calcium – Quick Facts — Retrieved 2013-08-23
  39. ^ Combs, G (2008). The Vitamins. Academic Press. p. 161. ISBN 0-12-183490-5. 
  40. ^ a b Weaver, CM (2006). "29 Calcium". In Barbara A. Bowman, Robert M. Russell. Present Knowledge in Nutrition I (9th ed.). ILSI Press. p. 377. ISBN 1-57881-198-8. 
  41. ^ Remington, Joseph (2005). Remington: The Science and Practice of Pharmacy. Lippincott Williams & Wilkins. p. 1338. ISBN 0-7817-4673-6. 
  42. ^ Zhao, Y; Martin, BR; Weaver, CM (2005). "Calcium bioavailability of calcium carbonate fortified soy milk is equivalent to cow's milk in young women". J. Nutr. 135 (10): 2379–82. PMID 16177199. 
  43. ^ Martini, Ligia and Wood, Richard J (2002). "Relative bioavailability of calcium-rich dietary sources in the elderly". American Journal of Clinical Nutrition 76 (6): 1345–1350. PMID 12450902. 
  44. ^ a b Straub, D. A. (2007). "Calcium Supplementation in Clinical Practice: A Review of Forms, Doses, and Indications". Nutrition in Clinical Practice 22 (3): 286–96. doi:10.1177/0115426507022003286. PMID 17507729. 
  45. ^ Martin, Berdine R.; Weaver, CM; Heaney, RP; Packard, PT; Smith, DL (2002). "Calcium Absorption from Three Salts and CaSO4-Fortified Bread in Premenopausal Women". Journal of Agricultural and Food Chemistry 50 (13): 3874–6. doi:10.1021/jf020065g. PMID 12059174. 
  46. ^ Weaver, Connie M.; Martin, BR; Costa, NM; Saleeb, FZ; Huth, PJ (2002). "Absorption of Calcium Fumarate Salts Is Equivalent to Other Calcium Salts When Measured in the Rat Model". Journal of Agricultural and Food Chemistry 50 (17): 4974–5. doi:10.1021/jf0200422. PMID 12166992. 
  47. ^ M. J. Bolland, A. Grey, A. Avenell, G. D. Gamble, I. R. Reid. (2011). "Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women's Health Initiative limited access dataset and meta-analysis." BMJ;342:d2040 DOI: 10.1136/bmj.d2040
  48. ^ Downing L, Islam MA (July 2013). "Influence of calcium supplements on the occurrence of cardiovascular events". Am J Health Syst Pharm (Review) 70 (13): 1132–9. doi:10.2146/ajhp120421. PMID 23784160. 
  49. ^ Dawson-Hughes B, Harris SS, Krall EA, Dallal GE (1997). "Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older". N. Engl. J. Med. 337 (10): 670–6. doi:10.1056/NEJM199709043371003. PMID 9278463. 
  50. ^ Jackson RD, LaCroix AZ, Gass M (2006). "Calcium plus vitamin D supplementation and the risk of fractures". N. Engl. J. Med. 354 (7): 669–83. doi:10.1056/NEJMoa055218. PMID 16481635. 
  51. ^ Grant AM, Avenell A, Campbell MK (2005). "Oral vitamin D3 and calcium for secondary prevention of low-trauma fractures in elderly people (Randomised Evaluation of Calcium Or vitamin D, RECORD): a randomised placebo-controlled trial". Lancet 365 (9471): 1621–8. doi:10.1016/S0140-6736(05)63013-9. PMID 15885294. 
  52. ^ Porthouse J, Cockayne S, King C (2005). "Randomised controlled trial of calcium and supplementation with cholecalciferol (vitamin D3) for prevention of fractures in primary care". BMJ 330 (7498): 1003. doi:10.1136/bmj.330.7498.1003. PMC 557150. PMID 15860827. 
  53. ^ Prince RL, Devine A, Dhaliwal SS, Dick IM (2006). "Effects of calcium supplementation on clinical fracture and bone structure: results of a 5-year, double-blind, placebo-controlled trial in elderly women". Arch. Intern. Med. 166 (8): 869–75. doi:10.1001/archinte.166.8.869. PMID 16636212. 
  54. ^ Fletcher RH (2006). "Calcium plus vitamin D did not prevent hip fracture or colorectal cancer in postmenopausal women" (subscription required). ACP J. Club 145 (1): 4–5. PMID 16813354. 
  55. ^ Weingarten MA, Zalmanovici A, Yaphe J (2005). Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps. In Weingarten, Michael Asher. "Dietary calcium supplementation for preventing colorectal cancer, adenomatous polyps and calcium metabolisism disorder". Cochrane database of systematic reviews (Online) (3): CD003548. doi:10.1002/14651858.CD003548.pub3. PMID 16034903. 
  56. ^ Baron JA, Beach M, Mandel JS (1999). "Calcium supplements for the prevention of colorectal adenomas. Calcium Polyp Prevention Study Group". N. Engl. J. Med. 340 (2): 101–7. doi:10.1056/NEJM199901143400204. PMID 9887161. 
  57. ^ Bonithon-Kopp C, Kronborg O, Giacosa A, Räth U, Faivre J (2000). "Calcium and fibre supplementation in prevention of colorectal adenoma recurrence: a randomised intervention trial. European Cancer Prevention Organisation Study Group". Lancet 356 (9238): 1300–6. doi:10.1016/S0140-6736(00)02813-0. PMID 11073017. 
  58. ^ Lappe, JM; Travers-Gustafson, D; Davies, KM; Recker, RR; Heaney, RP (2007). "Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial". The American journal of clinical nutrition 85 (6): 1586–91. PMID 17556697. 
  59. ^ Wactawski-Wende J, Kotchen JM, Anderson GL (2006). "Calcium plus vitamin D supplementation and the risk of colorectal cancer". N. Engl. J. Med. 354 (7): 684–96. doi:10.1056/NEJMoa055222. PMID 16481636. 
  60. ^ Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP (2007). "Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial". Am. J. Clin. Nutr. 85 (6): 1586–91. PMID 17556697. 
  61. ^ Lin J, Manson JE, Lee IM, Cook NR, Buring JE, Zhang SM (2007). "Intakes of calcium and vitamin D and breast cancer risk in women". Arch. Intern. Med. 167 (10): 1050–9. doi:10.1001/archinte.167.10.1050. PMID 17533208. 
  62. ^ Lewis, R. J. (1996). Sax's Dangerous Properties of Industrial Materials (9 ed.). New York, NY: Van Nostrand Reinhold. p. 635. ISBN 0-471-37858-5. 
  63. ^ ITII. Toxic and Hazardous Industrial Chemicals Safety Manual. Tokyo, Japan: The International Technical Information Institute. 1988. p. 101. 
  64. ^ Rumack BH. POISINDEX. Information System Micromedex, Inc., Englewood, CO, 2010; CCIS Volume 143. Hall AH and Rumack BH (Eds)
  65. ^ Beall DP, Henslee HB, Webb HR, Scofield RH (2006). "Milk-alkali syndrome: a historical review and description of the modern version of the syndrome". Am. J. Med. Sci. 331 (5): 233–42. doi:10.1097/00000441-200605000-00001. PMID 16702792. 
  66. ^ Picolos MK and Orlander PR (2005). "Calcium carbonate toxicity: The updated milk-alkali syndrome; report of 3 cases and review of the literature". Endocrine Practice 4 (11): 272–80. doi:10.4158/EP.11.4.272. PMID 16006300. 
  67. ^ Singh, N.; Singh, P.; Hershman, J. (2000). "Effect of calcium carbonate on the absorption of levothyroxine". JAMA: the Journal of the American Medical Association 283 (21): 2822–2825. doi:10.1001/jama.283.21.2822. PMID 10838651.  edit
  68. ^ Harding, Anne. "Calcium May Help With Weight Loss". Retrieved 2007-07-10. 
  69. ^ Michaëlsson K, Melhus H, Warensjö Lemming E, Wolk A, Byberg L (2013). "Long term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study". BMJ 346: f228. doi:10.1136/bmj.f228. PMC 3571949. PMID 23403980. 
  70. ^ Xiao Q, Murphy RA, Houston DK, Harris TB, Chow WH, Park Y (2013). "Dietary and supplemental calcium intake and cardiovascular disease mortality: the National Institutes of Health-AARP diet and health study". JAMA Internal Medicine 173 (8): 639–646. doi:10.1001/jamainternmed.2013.3283. PMC 3756477. PMID 23381719. 

Further reading

External links