'Calcium' (
IPA: ) is the
chemical element in the
periodic table that has the symbol 'Ca' and
atomic number 20. It has an atomic mass of 40.078. Calcium is a soft grey
alkaline earth metal, and is the fifth most abundant element in the
Earth's crust. It is essential for living
organisms, particularly in
cell physiology, and is the most common
metal in many
animals.
Notable characteristics
Calcium is a rather soft (though harder than lead), gray, metallic element that can be extracted by
electrolysis from fused
calcium chloride.
[1] It burns with a yellow-red flame and forms a white
nitride coating when exposed to air. It reacts with
water, displacing a hydrogen atom from the structure, then forming
calcium hydroxide.
The most abundant isotope,
40Ca, has a nucleus of 20
protons and 20
neutrons. Its
electron configuration is 2
electrons in the K shell (principal quantum number 1), 8 in the L shell (principal quantum number 2), 8 in the M shell (principal quantum number 3), and 2 in the N shell (principal quantum number 4). The outer shell is the valence shell, with 2 electrons in the lone 4s orbital, the 3d orbitals being empty.
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 occurs in
igneous and
metamorphic rocks chiefly in the
silicate minerals:
plagioclase,
amphiboles,
pyroxenes and
garnets.
''See also .''
Applications
Some uses are:
★ as a
reducing agent in the extraction of other metals, such as
uranium,
zirconium, and
thorium.
★ as a deoxidizer, desulfurizer, or decarbonizer for various
ferrous and nonferrous
alloys.
★ as an alloying agent used in the production of
aluminium,
beryllium,
copper,
lead, and
magnesium alloys.
★ in the making of
cements and
mortars to be used in
construction.
Calcium compounds
★
Calcium Carbonate (CaCO
3) used in manufacturing
cement and
mortar,
lime,
limestone (usually used in the steel industry); aids in production in the glass industry, also has chemical and optical uses as mineral specimens in
toothpastes for example.
★
Calcium arsenate (Ca
3(AsO
4)
2) is used in
insecticides.
★
Calcium carbide (CaC
2) is used: to make
acetylene gas (for use in acetylene
torches for
welding) and in the manufacturing of
plastics.
★
Calcium chloride (CaCl
2) is used: in
ice removal and
dust control on dirt roads, in
conditioner for
concrete, as an additive in canned
tomatoes, and to provide body for
automobile tires.
★ Calcium cyclamate (Ca(C
6H
11NHSO
4)
2) was used as a sweetening agent but is no longer permitted for use because of suspected cancer-causing properties.
★ Calcium gluconate (Ca(C
6H
11O
7)
2) is used as a
food additive and in
vitamin pills.
★
Calcium hypochlorite (Ca(OCl)
2) is used: as a
swimming pool disinfectant, as a
bleaching agent, as an ingredient in
deodorant, and in
algicide and
fungicide.
★ Calcium permanganate (Ca(MnO
4)
2) is used in liquid rocket propellant,
textile production, as a water sterilizing agent and in dental procedures.
★
Calcium phosphate (Ca
3(PO
4)
2) is used as a supplement for
animal feed,
fertilizer, in commercial production for
dough and
yeast products, in the manufacture of
glass, and in dental products.
★
Calcium phosphide (Ca
3P
2) is used in
fireworks,
rodenticide,
torpedoes and
flares.
★
Calcium stearate (Ca(C
18H
35O
2)
2 is used in the manufacture of
wax crayons,
cements, certain kinds of
plastics and
cosmetics, as a
food additive, in the production of water resistant materials and in the production of
paints.
★
Calcium sulfate (CaSO
4·2H
2O) is used as common blackboard chalk, as well as, in its hemihydrate form being more well known as Plaster of Paris.
★
Calcium tungstate (CaWO
4) is used in luminous
paints,
fluorescent lights and in
X-ray studies.
H and K lines
In the visible portion of the spectrum of many stars, including the
Sun, show 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. For the Sun and stars with low temperatures, the prominence of the H and K lines 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.
[2]
History
Calcium (
Latin ''calx,'' meaning "limestone") was known as early as the first century when the
Ancient Romans prepared lime as
calcium oxide. It was not isolated until 1808 in
England when
Sir Humphry Davy electrolyzed a mixture of lime and mercuric oxide. Davy was trying to isolate calcium; when he heard that 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
magnesium,
strontium and
barium.
Other compounds include
Calcium carbonate (CaCO
3), one of the common compounds of calcium. It is heated to form quicklime (CaO), which is then added to water (H
2O). 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.
Compounds
Calcium, combined with
phosphate to form
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 oxide (lime) is used in many chemical refinery processes and is made by heating and carefully adding water to
limestone. 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.
When water percolates through
limestone or other soluble
carbonate rocks, it partially dissolves part of the rock and causes cave formation and characteristic
stalactites and
stalagmites and also forms
hard water. Other important calcium compounds are
nitrate,
sulfide,
chloride,
carbide,
cyanamide, and
hypochlorite.
Isotopes
Main articles: Isotopes of calcium
Calcium has four stable
isotopes (
40Ca and
42Ca through
44Ca), plus two more isotopes (
46Ca and
48Ca) that have such long half-lives that for all practical purposes they can be considered stable. It 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.
97% 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.
Nutrition
| Age | Calcium (mg/day) |
|---|
| 0–6 months | 210 |
| 7–12 months | 270 |
| 1–3 years | 500 |
| 4–8 years | 800 |
| 9–18 years | 1300 |
| 19–50 years | 1000 |
| 51+ years | 1200 |
Calcium is an important component of a
healthy diet. A deficit can affect bone and tooth formation, while overretention can cause hypercalcemia (elevated levels of calcium in the blood), impaired kidney function and decreased absorption of other minerals.
[3] High calcium intakes or high calcium absorption were previously thought to contribute to the development of kidney stones. However, more recent studies show that high dietary calcium intakes actually decrease the risk for kidney stones.
[4] Vitamin D is needed to absorb calcium.
Dairy products, such as milk and cheese, are a well-known source of calcium. However, some individuals are allergic to dairy products and even more people, particularly those of non Indo-European descent, are
lactose-intolerant, leaving them unable to consume dairy products. Others, such as
vegans, avoid dairy products for ethical and health reasons. Fortunately, many other good sources of calcium exist. These include
seaweeds such as
kelp,
wakame and
hijiki; nuts and seeds (like
almonds and
sesame); blackstrap
molasses;
beans;
oranges;
amaranth;
collard greens;
okra;
rutabaga;
broccoli;
dandelion leaves;
kale;
sardines; and fortified products such as orange juice and
soy milk. The calcium content of most foods can be found in the USDA National Nutrient Database.
[5]
Calcium is essential for the normal growth and maintenance of bones and teeth, and calcium requirements must be met throughout life. Long-term calcium deficiency can lead to
osteoporosis, in which the bone deteriorates and there is an increased risk of fractures. Calcium has also been found to assist in the production of
lymphatic fluids.
Recommended Adequate Intake by the IOM for Calcium:
[6]
For more information about calcium in living nature, see
calcium in biology and
calcium metabolism.
Dietary calcium supplements
Calcium supplements are used to prevent and to treat calcium deficiencies. There are conflicting recommendations about when to take calcium supplements. However, most experts agree that no more than 500 mg should be taken at a time because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases.
It is recommended to spread doses throughout the day, with the last dose near bedtime. Recommended daily calcium intake varies from 1000 to 1500 mg, depending upon the stage of life.
In July 2006, a report citing research from
Fred Hutchinson Cancer Research Center in Seattle, Washington claimed that women in their 50s gained 5 pounds less in a period of 10 years by taking more than 500 mg of calcium supplements than those who did not. However, the doctor in charge of the study, Dr. Alejandro J. Gonzalez also noted it would be stretching it to suggest calcium supplements as a weight-limiting aid.
[7]
★
Calcium carbonate is the most common and least expensive calcium supplement. It can be difficult to digest and causes gas in some people. Taking magnesium with it can help to prevent constipation. Calcium carbonate is 40% elemental calcium. 1000 mg will provide 400 mg of calcium. It is recommended to take this supplement with food to aid in absorption. In some calcium supplements based on calcium carbonate,
vitamin D is added to aid in absorption. Vitamin D is needed for the absorption of calcium from the stomach and for the functioning of calcium in the body.
[8][9]
★
Calcium citrate is more easily absorbed (
bioavailability is 2.5 times higher than calcium carbonate), easier to digest and less likely to cause constipation and gas than calcium carbonate. It also has a lower risk of contributing to the formation of kidney stones. Calcium citrate is about 21% elemental calcium. 1000 mg will provide 210 mg of calcium. It is more expensive than calcium carbonate and more of it must be taken to get the same amount of calcium.
★
Calcium phosphate costs more than calcium carbonate, but less than calcium citrate. It is easily absorbed and is less likely to cause constipation and gas than either.
★
Calcium lactate and
calcium aspartate are both more difficult to digest and are more expensive than calcium carbonate
★ Calcium
chelates have been chemically bonded with an agent that the body recognizes as food. This form is generally known to be better absorbed by the human body than all other forms of calcium due to the bond.
The National Nutritional Food Association — NNFA (Newport Beach, Calif.) defines a chelate very specifically, and several criteria must be met in order for chelation to actually occur. Some of the claimed "chelates" on the market are the various
Krebs (Citric Acid) Cycle chelates, such as citrate, malate, and aspartate. Dicalcium malate (chelated with malic acid) is a newer form of a true calcium chelate. It contains a high amount of elemental calcium (30%).
Do calcium supplements prevent fractures due to osteoporosis?
Randomized controlled trials found both positive
[10][11] and negative
[12][13][14][15] benefit. The different results may be explained by doses of calcium and underlying rates of calcium supplementation in the control groups.
[16]
Do calcium supplements prevent cancer?
A
meta-analysis[11] by the international
Cochrane Collaboration of two
randomized controlled trials[18][19]found that calcium "might contribute to a moderate degree to the prevention of adenomatous
colonic polyps".
More recent studies were conflicting:
★ A
randomized controlled trial found that 1000 mg of elemental calcium and 400 IU of vitamin D
3 had no effect on colorectal cancer
[20]
★ A
randomized controlled trial found that 1400–1500 mg supplemental calcium and 1100 IU vitamin D
3 reduced aggregated cancers with a
relative risk of 0.402.
[21]
★ An observational
cohort study found that high calcium and vitamin D intake was associated with "lower risk of developing premenopausal breast cancer"
[22]
See also
★
Calcium metabolism
★
Calcium in biology
★
★
Disorders of calcium metabolism
Notes
1. Pauling, Linus ''General Chemistry'' p. 627, 1970 ed. Dover Publications
2. H-K Project Staff
3. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. Washington DC: The National Academies Press, 1997
4. Curhan G, Willett WC, Rimm E, Stampher MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8
5. USDA National Nutrient Database
6. Dietary Supplement Fact Sheet: Calcium
7. Calcium may help women keep weight in check
8. drugs.com article about Calcium with Vitamin D
9. Caltro
10. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older, Dawson-Hughes B, Harris SS, Krall EA, Dallal GE, , , N. Engl. J. Med., 1997
11. Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps, Weingarten MA, Zalmanovici A, Yaphe J, , , Cochrane database of systematic reviews (Online), 2005
12. Calcium plus vitamin D supplementation and the risk of fractures, Jackson RD, LaCroix AZ, Gass M, ''et al'', , , N. Engl. J. Med., 2006
13. 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, Grant AM, Avenell A, Campbell MK, ''et al'', , , Lancet, 2005
14. Randomised controlled trial of calcium and supplementation with cholecalciferol (vitamin D3) for prevention of fractures in primary care, Porthouse J, Cockayne S, King C, ''et al'', , , BMJ, 2005
15. Effects of calcium supplementation on clinical fracture and bone structure: results of a 5-year, double-blind, placebo-controlled trial in elderly women, Prince RL, Devine A, Dhaliwal SS, Dick IM, , , Arch. Intern. Med., 2006
16. Calcium plus vitamin D did not prevent hip fracture or colorectal cancer in postmenopausal women, Fletcher RH, , , ACP J. Club, 2006
17. Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps, Weingarten MA, Zalmanovici A, Yaphe J, , , Cochrane database of systematic reviews (Online), 2005
18. Calcium supplements for the prevention of colorectal adenomas. Calcium Polyp Prevention Study Group, Baron JA, Beach M, Mandel JS, ''et al'', , , N. Engl. J. Med., 1999
19. Calcium and fibre supplementation in prevention of colorectal adenoma recurrence: a randomised intervention trial. European Cancer Prevention Organisation Study Group, Bonithon-Kopp C, Kronborg O, Giacosa A, Räth U, Faivre J, , , Lancet, 2000
20. Calcium plus vitamin D supplementation and the risk of colorectal cancer, Wactawski-Wende J, Kotchen JM, Anderson GL, ''et al'', , , N. Engl. J. Med., 2006
21. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial, Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP, , , Am. J. Clin. Nutr., 2007
22. Intakes of calcium and vitamin d and breast cancer risk in women, Lin J, Manson JE, Lee IM, Cook NR, Buring JE, Zhang SM, , , Arch. Intern. Med., 2007
References
★ Rebecca J. Donatelle. Health, The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.
External links
★
WebElements.com — Calcium
★
USDA National Nutrient Database, Calcium content of selected foods
العربية
中国
Français
Deutsch
Ελληνική
हिन्दी
Italiano
日本語
Português
Русский
Español
