calcium

(kăl'sē-əm)
n. (Symbol Ca)
A silvery, moderately hard metallic element that constitutes approximately 3 percent of the earth's crust and is a basic component of most animals and plants. It occurs naturally in limestone, gypsum, and fluorite, and its compounds are used to make plaster, quicklime, Portland cement, and metallurgic and electronic materials. Atomic number 20; atomic weight 40.08; melting point 842 to 848°C; boiling point 1,487°C; specific gravity 1.55; valence 2.

[Latin calx, calc-, lime; see calx + -IUM.]

View more Science videos

For more information on calcium, visit Britannica.com.

A chemical element, Ca, of atomic number 20, fifth among elements and third among metals in abundance in the Earth's crust. Calcium compounds make up 3.64% of the Earth's crust. The physical properties of calcium metal are given in the table. The metal is trimorphous and is harder than sodium, but softer than aluminum. Like beryllium and aluminum, but unlike the alkali metals, it will not cause burns on the skin. It is less reactive chemically than the alkali metals and the other alkaline-earth metals. See also Periodic table.

Properties of calcium metal

Property	Value
Atomic number	20
Atomic weight	40.08
Isotopes (stable)	40, 42, 43, 44, 46, 48
Atomic volume, cm3/g-atom	25.9
Crystal form	Face-centered cubic
Valence	2+
Ionic radius, nm	0.099
Electron configuration	2882
Boiling point, °C	1487(?)
Melting point, °C	810(?)
Density, g/cm3 at 20°C	1.55
Latent heat of vaporization at boiling point, kilojoules/g-atom	399

Occurrence of calcium is very widespread; it is found in every major land area of the world. This element is essential to plant and animal life, and is present in bones, teeth, eggshell, coral, and many soils. Calcium chloride is present in sea water to the extent of 0.15%.

Calcium metal is prepared industrially by the electrolysis of molten calcium chloride. Calcium chloride is obtained either by treatment of a carbonate ore with hydrochloric acid or as a waste product from the Solvay carbonate process. The pure metal may be machined in a lathe, threaded, sawed, extruded, drawn into wire, pressed, and hammered into plates.

In air, calcium forms a thin film of oxide and nitride, which protects it from further attack. At elevated temperatures, it burns in air to form largely the nitride. The commercially produced metal reacts easily with water and acids, yielding hydrogen that contains noticeable amounts of ammonia and hydrocarbons as impurities.

The metal is employed as an alloying agent for aluminum-bearing metal, as an aid in removing bismuth from lead, and as a controller for graphitic carbon in cast iron. It is also used as a deoxidizer in the manufacture of many steels, as a reducing agent in preparation of such metals as chromium, thorium, zirconium, and uranium, and as a separating material for gaseous mixtures of nitrogen and argon.

Calcium oxide, CaO, is made by the thermal decomposition of carbonate minerals in tall kilns using a continuous-feed process. The oxide is used in high-intensity arc lights (limelights) because of its unusual spectral features and as an industrial dehydrating agent. The metallurgical industry makes wide use of the oxide during the reduction of ferrous alloys.

Calcium hydroxide, Ca(OH)₂, is used in many applications where hydroxide ion is needed. During the slaking process for producing calcium hydroxide, the volume of the slaked lime [Ca(OH)₂] produced expands to twice that of quicklime (CaO), and because of this, it can be used for the splitting of rock or wood. Slaked lime is an excellent absorbent for carbon dioxide to produce the very insoluble carbonate.

Calcium silicide, CaSi, an electric-furnace product made from lime, silica, and a carbonaceous reducing agent, is useful as a steel deoxidizer. Calcium carbide, CaC₂, is produced by heating a mixture of lime and carbon to 5432°F (3000°C) in an electric furnace. The compound is an acetylide which yields acetylene upon hydrolysis. Acetylene is the starting material for a great number of chemicals important in the organic chemicals industry.

Pure calcium carbonate exists in two crystalline forms: calcite, the hexagonal form, which possesses the property of birefringence, and aragonite, the rhombohedral form. Naturally occurring carbonates are the most abundant of the calcium minerals. Iceland spar and calcite are essentially pure carbonate forms, whereas marble is a somewhat impure and much more compact variety which, because it may be given a high polish, is much in demand as a construction stone. Although calcium carbonate is quite insoluble in water, it has considerable solubility in water containing dissolved carbon dioxide, because in these solutions it dissolves to form the bicarbonate. This fact accounts for cave formation in which limestone deposits have been leached away by the acidic ground waters.

The halides of calcium include the phosphorescent fluoride, which is the most widely distributed calcium compound and which has important applications in spectroscopy. Calcium chloride has in the anhydrous form important deliquescent properties which make it useful as an industrial drying agent and as a dust quieter on roads. Calcium chloride hypochlorite (bleaching powder) is produced industrially by passing chlorine into slaked lime, and has been used as a bleaching agent and a water purifier. See also Chlorine.

Calcium sulfate dihydrate is the mineral gypsum. It constitutes the major portion of portland cement, and has been used to help reduce soil alkalinity. A hemihydrate of calcium sulfate, produced by heating gypsum at elevated temperatures, is sold under the commercial name plaster of paris.

Calcium is an invariable constituent of all plants because it is essential for their growth. It is contained both as a structural constituent and as a physiological ion. Calcium is found in all animals in the soft tissues, in tissue fluid, and in the skeletal structures. The bones of vertebrates contain calcium as calcium fluoride, as calcium carbonate, and as calcium phosphate.

---

The major inorganic component of bones and teeth; the total body content of an adult is about 1-1.5 kg (15-38 mol). The small amounts in blood plasma (2.1-2.6 mmol/L, 85-105 mg/L) and in tissues play a vital role in the excitability of nerve tissue, the control of muscle contraction and the integration and regulation of metabolic processes.

The absorption of calcium from the intestinal tract requires vitamin D, and together with parathyroid hormone, vitamin D also controls the body's calcium balance, mobilizing it from the bones to maintain the plasma concentration within a very narrow range. An unacceptably high plasma concentration of calcium is hypercalcaemia.

Loss of calcium from bones occurs as a normal part of the ageing process, and may lead to osteoporosis.

The richest sources of calcium are milk and cheese; in some countries it is added to flour. Other rich sources include: haggis, canned pilchards and sardines, spinach, sprats, tripe.

A metallic element essential for normal development and health. The average adult contains over 1 kg of calcium, stored mainly as calcium salts in the bones. Calcium is essential for the normal activity of muscles and nerves, for growth of bones and teeth, and for blood clotting.

In the United States, it is recommended that adults take 800 mg of calcium each day; in the UK, the Reference Nutrient Intake (RNI, the amount of nutrient sufficient for almost all individuals) is 700 mg per day. Higher RDAs are recommended for children, adolescents, pregnant and lactating mothers. In the USA, the National Institute of Health recommended that post-menopausal women should consume between 1200 and 1500 mg of calcium per day to reduce the risk of osteoporosis. Some nutritionists believe that this high level of intake after menopause has no benefit. The need for adequate calcium is greatest in adolescents and young adults, so as to maximize bone density. The higher the peak density, the longer the post-menopausal losses can continue without causing significant weakening of the bone. Regular exercise is also important to minimize mineral loss. Good sources of calcium are milk, cheese, yoghurt, legumes, nuts, and wholegrains. Vitamin D aids absorption.

About one-third of the dietary intake of calcium is egested in the faeces. Some is also excreted in the urine with the amount increasing among those on a high protein diet. Long-duration activity and high temperatures increase the amount of calcium lost in urine and sweat. Many sports coaches believe that these losses justify the use of calcium supplements by young women, especially elite endurance athletes who train at a relatively high intensity for long periods.

Excess calcium depresses some physiological activities associated with nerves and muscles and can lead to the development of kidney stones. Calcium deficiencies can slow down the growth rate of children and cause rickets. Deficiencies in adults may lead to the development of soft, inadequately mineralized bones (osteomalacia) and brittle bones. See also osteoporosis.

A mineral essential in building and maintaining bones and teeth, as well as in providing efficient muscle contraction and blood clotting. Calcium is found in dairy products, leafy green vegetables (such as spinach, turnip greens and broccoli), sardines and canned salmon with bones and rhubarb.

Calcium is crucial to all physiological function. It must be obtained from the diet, but since an intake of only about 1 g per day is adequate, shortage is rare; the net daily turnover (the absorption rate into blood, and excretion rate in the urine) is only about one-tenth of that amount again.

The average human body contains just over 1 kg of calcium, more than 99% of it in the skeleton (and teeth). Here it is mostly in the form of complex phosphate salts forming the rigid structures that allow bone to fulfil its essential supportive role. Skeletal calcium is not, however, inert. Bone contains cells that lay down new bone and resorb old bone and the regulated activities of these cells, made possible by the extensive blood supply that bone receives, ensure that skeletal calcium actively turns over. Beyond middle age, the rate of bone deposition fails to keep pace with its resorption and the disparity can become severe enough to cause osteoporosis, when the bones become fragile and fracture easily. In addition to its structural role, the skeleton serves also as a reservoir from which calcium can be mobilized if necessary.

Calcium absorption from the small intestine and excretion from the kidneys are also regulated to ensure that the concentration of calcium in the plasma is very precisely controlled, probably more tightly than any other component of plasma. The need for such precise calcium homeostasis is underscored by the serious consequences that follow deviations from the norm. Excessively low plasma calcium levels (hypocalcaemia) are particularly dangerous because they evoke spontaneous activity in both nerves and muscles, causing muscle spasms that can become so severe as to obstruct the airway. Conversely, with too high a plasma calcium level (hypercalcaemia), nerves and muscle can become less active, leading to weakness. The longer term consequences of aberrant plasma calcium regulation can include skeletal problems and kidney stones.

Three agents are principally responsible for plasma calcium regulation, acting directly or indirectly at the three sites where the amount entering or leaving the blood can be influenced — bone, kidneys, and intestine.

Parathyroid hormone is a peptide released from the parathyroid glands in the neck in direct response to any fall in the plasma calcium concentration. In bone it enhances calcium resorption and transfer into the blood. In the kidneys it both reduces calcium excretion and promotes formation of the active metabolite of vitamin D₃, which in turn enhances intestinal absorption. Thus parathyroid hormone helps to restore plasma calcium levels to normal.

Vitamin D (cholecalciferol) is not only a component of the diet (extra is added to cereals and dairy products) but also is synthesized in the skin in the presence of sunlight. After modification in the liver, vitamin D₃ is further modified to its active form in the kidneys, a step that is stimulated largely via parathyroid hormone, and hence in turn by a fall in the plasma calcium concentration. The active metabolite of vitamin D₃, 1, 25-dihydroxycholecalciferol (calcitriol) is a hormone that stimulates calcium uptake from the small intestine and mobilization of calcium from bone, both serving to reverse the fall in plasma calcium that triggered formation of the hormone initially. Defects in any of the pathways leading to formation of 1, 25-dihydroxycholecalciferol give rise to rickets.

Calcitonin is the third, and least important, calcium-regulating hormone. It is released from cells within the thyroid gland in response to an increase in plasma calcium and to several other factors, including gastrin, a hormone released during feeding and therefore heralding a potential rise in plasma calcium. Calcitonin serves to reverse any such rise by inhibiting bone resorption.

Clinical disorders of calcium regulation can arise for a variety of reasons, related not only directly to excess or deficiency of the relevant hormones, but also to conditions affecting kidney function and intestinal absorption; there can also be defects in the signalling proteins responsible for mediating the effects of parathyroid hormone on its target tissues. Conditions disturbing acid-base homeostasis can alter the concentration of free calcium ions in the blood: alkalinity increases, and acidity decreases their binding to proteins in the plasma.

It is ironic that the insolubility of calcium phosphate that allows it to form so stable a structure in bone was probably also the ultimate cause, in evolutionary terms, of calcium coming to fulfil its other indispensible role as a dynamic regulator of cellular activity. The energy economy of every cell is now dominated by the transfer of phosphate groups, and since calcium phosphate is so insoluble, it is likely that cells have long (in evolutionary terms) been required to actively extrude calcium. Every cell now maintains a very low free calcium ion concentration in its cytoplasm, some 10 000 times or so lower than that in either the plasma or the enclosed calcium stores within the cell. These very steep calcium concentration gradients are maintained by using energy, generated from the metabolism of the cell, to actively export calcium from the cytoplasm, either out of the cell or into the internal stores. There are two benefits of this active calcium transport. Firstly, it allows the energy economy of the cell to operate free of the risk that the key intermediates will be precipitated by calcium. Secondly, it provides steep, ready-made gradients down which calcium can rapidly flow into the cytoplasm when appropriate physiological stimuli cause the opening of calcium ion channels in either the plasma membrane or the membranes of the intracellular stores. Rigorously controlled leaking of calcium through such channels is ubiquitous in the regulation of cellular activity. The fertilization of an egg, every beat of the heart or contraction of any other muscle, release of transmitters from nerve endings — myriads of physiological responses — all are regulated by transient increases in cytoplasmic calcium ion concentration brought about by appropriate stimuli from outside the cell, that cause calcium channels to open, and allow movement down the gradient into the cell. The ensuing increase in cytoplasmic calcium concentration is detected by specific calcium-binding proteins, the most abundant of which is calmodulin. The change in shape of these proteins that follows their binding of calcium allows them to interact specifically with their targets within the cell; these include enzymes, ion channels, and muscle fibres. The intense scrutiny to which calcium channels have been subjected in recent decades has revealed their structures and the stimuli that control their opening (which range from changes in voltage to extracellular and intracellular messenger molecules) ; it is also beginning to establish the molecular mechanisms underlying their behaviour. Despite the diversity of behaviours, one feature that appears to be shared by all calcium channels is their regulation by cytoplasmic calcium ion concentration itself: each seems to be subject to feedback inhibition by calcium, a mechanism that probably serves to prevent intracellular calcium from rising to levels that could be toxic. This function can fail in sick cells — an excessive influx of calcium is known for example to be destructive to neuronal function when brain cells are damaged by lack of oxygen.

As well as these crucial roles in cellular function and in bone, ionized calcium in the blood plasma is one of several factors necessary for the clotting process: its chemical removal by the addition of citrate solution allows donor blood to be kept fluid for transfusion.

— C. W. Taylor

See also blood; body fluids; cell; ion channels; neuromuscular junction; parathyroid glands; synapse.

Brand names: Calcarb™ with Vitamin D, Calcet® Plus Vitamin D, Calcitrate™ with D, Caltrate® 600 Plus, Caltrate® Colon Health, Calvite P & D, Citracal® 250mg Plus D, Citracal® Creamy Bites, Citracal® Petites with Vitamin D, Citracal® Plus D, Citrus Calcium Plus D, Dical®, Dicalphos® Plus D, Flintstones® Bone Building Calcium Chews, GNC Coral Calcium, Olay™ Vitamins Wellness Nutrients Essential Bone Health Formula, Os-Cal® 250 with D, Os-Cal® 500 Plus D (no longer marketed), Os-Cal® with D, Oysco 500 Plus D, Oysco D, Oyst Calcium, Oyst-Cal®-D 500mg, Oyst-Cal-D®, Oystercal D™, Posture-D®

Drug Forms:
• Calcium Carbonate, Vitamin D Oral tablet (below)
• Calcium, Vitamin D Oral tablet
• Calcium; Vitamin D tablets
• Calcium Carbonate, Cholecalciferol Chewable tablet
• Cholecalciferol, Calcium Carbonate Oral tablet
• Calcium Carbonate, Vitamin D Chewable tablet
• Calcium Citrate, Cholecalciferol Oral tablet
• Calcium Citrate, Cholecalciferol Soft chew
• Calcium Stearate, Cholecalciferol Oral tablet
• Cholecalciferol, Calcium Oral tablet
• Calcium, Cholecalciferol Chewable tablet
• Calcium, Cholecalciferol Soft chew

Espa�ol:
• Carbonato de calcio; Vitamina D, Tableta oral
• Calcio, Vitamina D, Tableta oral
• Carbonato de calcio; Colecalciferol, Tableta masticable
• Carbonato de calcio; Colecalciferol, Tableta oral
• Carbonato de calcio; Vitamina D, Tableta masticable
• Citrato de calcio; Colecalciferol, Tableta oral
• Citrato De Calcio; Colecalciferol, Tableta masticable blanda
• Estearato de calcio; Colecalciferol, Tableta oral
• Colecalciferol, Calcio Tableta oral
• Calcio, Colecalciferol, Tableta masticable
• Calcio, Colecalciferol, Tableta masticable blanda

Calcium Carbonate, Vitamin D Oral tablet

What is this medicine?

CALCIUM; VITAMIN D (KAL see um; VYE ta min  D) is a vitamin supplement. It is used to prevent conditions of low calcium and vitamin D.
 
This medicine may be used for other purposes; ask your health care provider or pharmacist if you have questions.

What should I tell my health care provider before I take this medicine?

They need to know if you have any of these conditions:
•constipation
•dehydration
•heart disease
•high level of calcium or vitamin D in the blood
•high level of phosphate in the blood
•kidney disease
•kidney stones
•liver disease
•parathyroid disease
•sarcoidosis
•stomach ulcer or obstruction
•an unusual or allergic reaction to calcium, vitamin D, tartrazine dye, other medicines, foods, dyes, or preservatives
•pregnant or trying to get pregnant
•breast-feeding

How should I use this medicine?

Take this medicine by mouth with a glass of water. Follow the directions on the label. Take with food or within 1 hour after a meal. Take your medicine at regular intervals. Do not take your medicine more often than directed.

Talk to your pediatrician regarding the use of this medicine in children. While this medicine may be used in children for selected conditions, precautions do apply.

Overdosage: If you think you have taken too much of this medicine contact a poison control center or emergency room at once.
NOTE: This medicine is only for you. Do not share this medicine with others.

What if I miss a dose?

If it is almost time for your next dose, take only that dose. Do not take double or extra doses.

What may interact with this medicine?

Do not take this medicine with any of the following medications:
•ammonium chloride
•methenamine

This medicine may also interact with the following medications:
•antibiotics like ciprofloxacin, gatifloxacin, tetracycline
•captopril
•delavirdine
•diuretics
•gabapentin
•iron supplements
•medicines for fungal infections like ketoconazole and itraconazole
•medicines for seizures like ethotoin and phenytoin
•mineral oil
•mycophenolate
•other vitamins with calcium, vitamin D, or minerals
•quinidine
•rosuvastatin
•sucralfate
•thyroid medicine

This list may not describe all possible interactions. Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. Also tell them if you smoke, drink alcohol, or use illegal drugs. Some items may interact with your medicine.

What should I watch for while using this medicine?

Taking this medicine is not a substitute for a well-balanced diet and exercise. Talk with your doctor or health care provider and follow a healthy lifestyle.

Do not take this medicine with high-fiber foods, large amounts of alcohol, or drinks containing caffeine. Do not take this medicine within 2 hours of any other medicines.

What side effects may I notice from receiving this medicine?

Side effects that you should report to your doctor or health care professional as soon as possible:
•allergic reactions like skin rash, itching or hives, swelling of the face, lips, or tongue
•confusion
•dry mouth
•high blood pressure
•increased hunger or thirst
•increased urination
•irregular heartbeat
•metallic taste
•muscle or bone pain
•pain when urinating
•seizure
•unusually weak or tired
•weight loss

Side effects that usually do not require medical attention (report to your doctor or health care professional if they continue or are bothersome):
•constipation
•diarrhea
•headache
•loss of appetite
•nausea, vomiting
•stomach upset

This list may not describe all possible side effects. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Where should I keep my medicine?

Keep out of the reach of children.

Store at room temperature between 15 and 30 degrees C (59 and 86 degrees F). Protect from light. Keep container tightly closed. Throw away any unused medicine after the expiration date.

Last updated: 11/16/2005 10:49:00 AM

Important Disclaimer: The drug information provided here is for educational purposes only. It is intended to supplement, not substitute for, the diagnosis, treatment and advice of a medical professional. This drug information does not cover all possible uses, precautions, side effects and interactions. It should not be construed to indicate that this or any drug is safe for you. Consult your medical professional for guidance before using any prescription or over the counter drugs.

A metallic element essential for the normal development and functioning of the body. It is required for many metabolic processes, including nerve function, muscle contraction, and blood clotting, and it is an important constituent of bones and teeth. Calcium is maintained at the correct concentration in the blood by the action of hormones (see calcitonin (salmon); parathyroid hormone). The uptake of calcium from the gut and its deposition in bone is facilitated by vitamin D; deficiency of this vitamin may therefore result in bone disorders, such as rickets in children and osteoporosis or osteomalacia in adults. Deficiency of calcium in the blood leads to tetany (spasm and twitching of the muscles). Conversely, high plasma concentrations of calcium may lead to the deposition of calcium in soft tissues and cause 'hardening' of the tissues (calcification).

Calcium supplements are given to prevent or treat calcium deficiency. Extra calcium may be required by growing children, pregnant or breastfeeding women, women who have reached the menopause, and elderly people; it reduces bone loss in people with osteoporosis. Supplementary calcium may also be required by people who cannot tolerate milk. Oral calcium supplements are available as a variety of calcium salts, including calcium carbonate, calcium gluconate, calcium lactate, calcium lactate gluconate, calcium phosphate, calcium glubionate, and calcium lactobionate, which are readily absorbed. They are often packaged with vitamin D. Calcium gluconate and calcium chloride can be given intravenously. Calcium salts are also used in antacid preparations.

Side effects:
include constipation and flatulence. Injections may cause slowing of the heart rate, irregular heartbeat, and irritation.

Precautions:
calcium supplements should not be taken by people with conditions associated with high plasma calcium concentrations or tissue calcification (including some forms of cancer and kidney disease) or by those who are immobile for long periods (since prolonged immobilization causes resorption of calcium from bone and high plasma calcium concentrations).

Interactions with other drugs:

Antibiotics the absorption of tetracyclines and ciprofloxacin is reduced by calcium salts.
Bisphosphonates their absorption is reduced by calcium salts.
Digoxin and digitoxin: calcium given by intravenous injection can cause irregular heartbeats.
Thiazide diuretics the risk of high blood calcium concentrations is increased.

Previous:	calcitriol, calcitonin, calcipotriol
Next:	calcium acetate, calcium antagonists, calcium carbonate

A mineral essential for normal development of bone and teeth, and for the maintenance of overall health. Calcium is required for blood clotting, muscle and nerve activity, and cell permeability. It is the most abundant mineral in the body (over 1 kg is contained in the average adult). The recommended daily calcium intake varies for different groups, but in 2000 the US National Institute of Health recommended that adolescent girls consume 1500 mg daily to maximize bone density and reduce the risk of osteoporosis in later years. Sources of calcium include milk, meat, fish, poultry, legumes, nuts, and whole-grains. Its absorption is aided by vitamin D. About one-third of the dietary intake of calcium is lost in the faeces. Losses in urine and sweat increase during vigorous activity. These extra losses are used to justify the use of calcium supplements by some elite athletes, but studies indicate that supplementation is of no value to athletes whose dietary intake equals the recommended levels. Consumption of calcium in excess of 2500 mg daily may reduce zinc absorption, depress neural and motor functions and can lead to the development of kidney stones. Calcium deficiency can retard growth and cause rickets in children. Deficiencies may lead to osteomalacia and osteoporosis in adults.

Calcium is one of the most important elements in the diet because it is a structural component of bones, teeth, and soft tissues and is essential in many of the body's metabolic processes. It accounts for 1 to 2 percent of adult body weight, 99 percent of which is stored in bones and teeth. On the cellular level, calcium is used to regulate the permeability and electrical properties of biological membranes (such as cell walls), which in turn control muscle and nerve functions, glandular secretions, and blood vessel dilation and contraction. Calcium is also essential for proper blood clotting.

Because of its biological importance, calcium levels are carefully controlled in various compartments of the body. The three major regulators of blood calcium are parathyroid hormone (PTH), vitamin D, and calcitonin. PTH is normally released by the four parathyroid glands in the neck in response to low calcium levels in the bloodstream (hypocalcemia). PTH acts in three main ways: (1) It causes the gastrointestinal tract to increase calcium absorption from food, (2) it causes the bones to release some of their calcium stores, and (3) it causes the kidneys to excrete more phosphorous, which indirectly raises calcium levels.

Vitamin D works together with PTH on the bone and kidney and is necessary for intestinal absorption of calcium. Vitamin D can either be obtained from the diet or produced in the skin when it is exposed to sunlight. Insufficient vitamin D from these sources can result in rickets in children and osteomalacia in adults, conditions that result in bone deformities. Calcitonin, a hormone released by the thyroid, parathyroid, and thymus glands, lowers blood levels by promoting the deposition of calcium into bone.

Most dietary calcium is absorbed in the small intestine and transported in the bloodstream bound to albumin, a simple protein. Because of this method of transport, levels of albumin can also influence blood calcium measurements. Calcium is deposited in bone with phosphorous in a crystalline form of calcium phosphate.

Deficiency and Toxicity
Because bone stores of calcium can be used to maintain adequate blood calcium levels, short-term dietary deficiency of calcium generally does not result in significantly low blood calcium levels. But, over the long term, dietary deficiency eventually depletes bone stores, rendering the bones weak and prone to fracture. A low blood calcium level is more often the result of a disturbance in the body's calcium regulating mechanisms, such as insufficient PTH or vitamin D, rather than dietary deficiency. When calcium levels fall too low, nerve and muscle impairments can result. Skeletal muscles can spasm and the heart can beat abnormally—it can even cease functioning.

Toxicity from calcium is not common because the gastrointestinal tract normally limits the amount of calcium absorbed. Therefore, short-term intake of large amounts of calcium does not generally produce any ill effects aside from constipation and an increased risk of kidney stones. However, more severe toxicity can occur when excess calcium is ingested over long periods, or when calcium is combined with increased amounts of vitamin D, which increases calcium absorption. Calcium toxicity is also sometimes found after excessive intravenous administration of calcium. Toxicity is manifested by abnormal deposition of calcium in tissues and by elevated blood calcium levels (hypercalcemia). However, hypercalcemia is often due to other causes, such as abnormally high amounts of PTH. Usually, under these circumstances, bone density is lost and the resulting hypercalcemia can cause kidney stones and abdominal pain. Some cancers can also cause hypercalcemia, either by secreting abnormal proteins that act like PTH or by invading and killing bone cells causing them to release calcium. Very high levels of calcium can result in appetite loss, nausea, vomiting, abdominal pain, confusion, seizures, and even coma.

Requirements and Supplementation
Dietary calcium requirements depend in part upon whether the body is growing or making new bone or milk. Requirements are therefore greatest during childhood, adolescence, pregnancy, and breastfeeding. Recommended daily intake (of elemental calcium) varies accordingly: 400 mg for infants 0–6 months, 600 mg for infants 6–12 months, 800 mg for children 1–10 years, 1,200 mg for ages 11–24 years, and 800 mg for individuals over 24 years of age. Pregnant women require additional calcium (RDA 1,200 mg). Many experts believe that elderly persons should take as much as 1,500 mg to help prevent osteoporosis, a common condition in which bones become weak and fracture easily due to a loss of bone density. Dairy products, meats, and some seafood (sardines, oysters) are excellent sources of calcium. Spinach, beet greens, beans, and peanuts are among the best plant-derived sources.

Calcium absorption is affected by many factors, including age, the amount needed, and what foods are eaten at the same time. In general, calcium from food sources is better absorbed than calcium taken as supplements. Children absorb a higher percentage of their ingested calcium than adults because their needs during growth spurts may be two or three times greater per body weight than adults. Vitamin D is necessary for intestinal absorption, making Vitamin D–fortified milk a very well-absorbed form of calcium. Older persons may not consume or make as much vitamin D as is optimal, so their calcium absorption may be decreased. Vitamin C and lactose (the sugar found in milk) enhance calcium absorption, whereas meals high in fat or protein may decrease absorption. Excess phosphorous consumption (as in carbonated sodas) can decrease calcium absorption in the intestines. High dietary fiber and phytate (a form of phytic acid found in dietary fiber and the husks of whole grains) may also decrease dietary calcium absorption in some areas of the world. Intestinal pH also affects calcium absorption—absorption is optimal with normal stomach acidity generated at meal times. Thus, persons with reduced stomach acidity (e.g., elderly persons, or persons on acid-reducing medicines) do not absorb calcium as well as others do.

Supplement	Elemental calcium by weight	Comment
Calcium carbonate	40%	• Most commonly used • Less well absorbed in persons with decreased stomach acid (e.g., elderly or those on anti-acid medicines) • Natural preparations from oyster shell or bone meal may contain contaminants such as lead • Least expensive
Calcium citrate	21%	• Better absorbed, especially by those with decreased stomach acid • May protect against kidney stones • More expensive.
Calcium phosphate	38% or 31%	• Tricalcium or dicalcium phosphate • Used more in Europe • Absorption similar to calcium carbonate
Calcium gluconate	9%	• Used intravenously for severe hypocalcemia • Well absorbed orally, but low content of elemental calcium • Very expensive
Calcium glubionate	6.5%	• Available as syrup for children • Low content elemental calcium.
Calcium lactate	13%	• Well absorbed, but low content elemental calcium.
SOURCE: Gregory, Philip J. (2000) "Calcium Salts." Prescriber's Letter. Document #160313.

Calcium supplements are widely used in the treatment and prevention of osteoporosis. Supplements are also recommended, or are being investigated, for a number of conditions, including hypertension, colon cancer, cardiovascular disease, premenstrual syndrome, obesity, stroke, and preeclampsia (a complication of pregnancy). There are several forms of calcium salts used as supplements. They vary in their content of elemental calcium, the amount effectively absorbed by the body, and cost. Whatever the specific form, the supplement should be taken with meals to maximize absorption.

Calcium is one of the most important macronutrients for the body's growth and function. Sufficient amounts are important in preventing many diseases. Calcium levels are tightly controlled by a complex interaction of hormones and vitamins. Dietary requirements vary throughout life and are greatest during periods of growth and pregnancy. However, recent reports suggest that many people do not get sufficient amounts of calcium in their diet. Various calcium supplements are available when dietary intake is inadequate.

See also Minerals; Osteomalacia; Osteoporosis; Rickets.

Bibliography
Berkow, Robert, ed. (1997). The Merck Manual of Medical Information, Home Edition. Whitehouse Station, NJ: Merck & Co.
National Research Council (1989). Recommended Dietary Allowances, 10th edition. Washington, DC: National Academy Press.
Olendorf, Donna; Jeryan, Christine; and Boyden, Karen, eds. (1999). The Gale Encyclopedia of Medicine. Farmington Hills, MI: Gale Research.

Internet Resources
Food and Nutrition Board (1999). Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press. Available from http://www.nap.edu
Gregory, Philip J. (2000) "Calcium Salts." Prescriber's Letter Document #160313. Available from http://www.prescribersletter.com

KEY TERMS Dietary supplement—A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual’s diet with the expectation that it will improve health. Diuretic—A substance that removes water from the body by increasing urine production. Electrolyte—Electrically charged particles (ions) that form when salts dissolve in water or fluids. Electrolytes regulate water balance in the body and play a critical role in almost every metabolic reaction. Enzyme—Proteins that change the rate of a chemical reaction within the body without themselves being used up in the reaction. Mineral—An inorganic substance found in the earth that is necessary in small quantities for the body to maintain a health. Examples: zinc, copper, iron.

    Description
    Precautions
    Interactions
    Complications
    Parental concerns
    Resources

What is Calcium?

Calcium (Ca) is the most abundant mineral in the body. About 99% of calcium in the body is in bones and teeth. The remaining 1% is in blood and soft tissue. Calcium in body fluids is an electrolyte with a charge of + 2. Humans must meet their need for calcium through diet.

What is the Purpose of Calcium?

Calcium is essential for:

• building and maintaining strong bones and teeth.
• muscle contraction.
• blood vessel contraction and relaxation.
• nerve impulse transmission.
• regulating fluid balance in the body.

Calcium.

Age	Recommended dietaryallowance(mg)	Tolerable upper intake level(mg)
Children 0–6 mos.	210 (AI)	Not established
Children 7–12 mos.	270 (AI)	Not established
Children 1–3 yrs.	500	2,500
Children 4–8 yrs.	800	2,500
Children 9–13 yrs.	900	2,500
Adolescents 14–18 yrs.	1,300	2,500
Adults 19-50 yrs.	1,000	2,500
Adults 50>yrs.	1,200	2,500
Pregnant women 18≤yrs.	1,300	2,500
Pregnant women 19≥yrs.	1,000	2,500
Breastfeeding women 18≤yrs.	1,300	2,500
Breastfeeding women 19≥yrs.	1,000	2,500
Food	Calcium(mg)
Yogurt, plain, 1 cup	415
Cheese, mozzarella, 1.5 oz.	372
Sardines with bones, canned in oil, 3 oz.	324
Cheese, cheddar, 1.5 oz.	305
Milk, any type, 1 cup	300
Yogurt with fruit, 1 cup	245–384
Tofu, firm, with calcium sulfate, 1/2 cup	204
Orange juice, fortified, 6 oz.	200–260
Salmon with bones, canned, 3 oz.	181
Spinach, cooked, 1/2 cup	120
Beans, white, cooked, 1/2 cup	113
Instant breakfast drink, powder, prepared with water	105–250
Cereal, fortified, 1 cup	100– 1,000
Bok choy, cooked, 1/2 cup	61
Beans, pinto or red, cooked, 1/2 cup	43
Bread, whole wheat, 1 slice	20
AI=Adequate intake
mg=milligram

---

Calcium (Ca²) is a silver-white metallic element of the alkaline-earth group. Ninety-nine percent of calcium in the human body is in bone and teeth. The remaining one percent is in blood and body fluids. In addition to its role in maintaining strength of bone and teeth, calcium is involved in nerve cell function, control of muscle tone, and blood clot formation. Calcium is also necessary in order for many important proteins to properly perform critical metabolic functions throughout the body.

Functions

Cells. Calcium concentrations in the fluids outside cells are much larger than calcium concentrations inside cells (the cytosol). Unequal calcium concentrations in the extracellular fluid and cytosol are required for cells to carry out many crucial functions. For example, when a hormone in the blood binds to a receptor on the cell, calcium pours into the cytosol from extracellular fluid. This change in the amount of calcium in the cytosol signals the cell to perform some critical function. The critical function that is triggered depends on the type of cell. (In muscle cells, for example, a nerve signal triggers the release of calcium into the cytosol, allowing muscle contraction to occur.) After the critical function is performed, calcium is rapidly pumped out of the cell, and the calcium concentration in the cytosol returns to the normal (low) level.

Structural. In addition to cellular functions, calcium's more familiar role is a structural one—as a component of bones and teeth. Blood calcium levels are maintained strictly even if calcium has to be taken from bone. Bone mineral (hydroxyapatite) is made up primarily of calcium, phosphate, and carbonate. Bone constantly changes during growth and throughout adulthood. Changes in bone occur through balancing activities of bone-destroying cells (osteoclasts) and bone-forming cells (osteoblasts), which act together to remove and replace bone, respectively. During growth, bone formation generally exceeds destruction, yielding net bone-mass gain in the whole skeleton.

Bone-mass accumulation continues until peak bone mass is achieved, generally during the third decade of life. The age at which peak bone mass is reached varies by gender and differs by skeletal site. Males achieve peak bone mass later than females and gain more bone during puberty than females, resulting in larger bones. Although peak bone mass at all skeletal sites is generally reached by age thirty, bone accumulation is nearly complete by age twenty in the lumbar spine and in portions of the hip for both males and females. Genetic, environmental (for example, physical activity or mechanical "loading" of the skeleton), hormonal, and nutritional factors interact to influence peak bone-mass levels. Failure of an individual to reach the maximum peak bone mass permitted by his or her genetic makeup can be related to low calcium intake or a sedentary lifestyle without adequate physical activity. Parathyroid dysfunction, genetic or nutritional skeletal disorders, or medication use may affect peak bone-mass accumulation and overall bone health adversely. Smoking and excessive alcohol consumption also are likely to be detrimental to skeletal health.

After an individual reaches peak bone mass, net bone gain in the whole skeleton generally does not occur. Agerelated bone loss occurs in both genders, but the rate of bone loss increases with estrogen loss at menopause in females. Age-related bone loss is caused by increased osteoclast (bone-destroying) activity compared to osteoblast (bone-building) activity. Physical activity during adulthood, combined with adequate overall nutrition and calcium intake, can help to maintain bone strength.

Metabolism

Absorption. Calcium absorption across the intestinal wall into the blood occurs by different mechanisms. Two major mechanisms include passive diffusion and active transport. Vitamin D is required for the active transport mechanism but not for the passive diffusion mechanism. The percent of calcium that is absorbed into blood generally decreases with higher calcium intakes; however, the total amount of calcium absorbed is usually greater with higher calcium intakes. The percent of calcium absorbed into blood is highest in infants, spikes again at the start of puberty, then gradually declines with age. The percent of calcium absorbed into blood also increases during the last two trimesters of pregnancy.

Homeostasis. The body keeps tight control (homeostasis) of blood calcium concentration by continuously changing various factors. When blood calcium concentration falls below normal, the parathyroid gland releases parathyroid hormone (PTH). PTH stimulates increased removal of phosphate into urine by the kidneys. This increased phosphate removal triggers the kidneys to keep calcium in the blood rather than excrete it in the urine. PTH also stimulates osteoclasts to remove calcium from bone in order to help restore normal blood calcium concentration. Finally, PTH is involved in making certain that enough vitamin D is present in the intestine to allow for increased calcium absorption from the gut into the blood. PTH decreases to normal once calcium homeostasis is reached. Another hormone, calcitonin, is responsible for stopping bone breakdown by osteoclasts when blood calcium concentration is above normal. Thus, the hormones PTH and calcitonin work together to keep blood calcium concentration within a very narrow range.

Dietary Requirements

Bioavailability. Both dairy products and most dietary supplements provide adequate amounts of calcium. Calcium is present in smaller amounts in grains, fruits, and vegetables. Because grains are eaten in high amounts, however, they are an important source of calcium. Other calcium-rich foods include bok choy (Chinese cabbage), kale, cabbage, and broccoli. Calcium from some foods containing high levels of oxalic acid (spinach, sweet potatoes, rhubarb, beans) or phytic acid (unleavened bread, nuts and grains, seeds, raw beans) is absorbed poorly due to formation of insoluble calcium salts. The ability to enhance dietary calcium intake by consuming calcium-fortified food sources is increasingly common.

Although high protein intake temporarily increases urinary calcium excretion, there is no evidence to indicate that calcium intake recommendations should be adjusted according to protein intake. Although caffeine has a slightly negative impact on calcium retention, the modest calcium loss can be offset by a similarly modest increase in calcium intake. High salt (sodium chloride) intake usually results in increased urinary calcium loss because excretion of sodium and calcium at the kidney are linked. High salt intake triggers increased urinary sodium loss and, therefore, increased urinary calcium excretion. However, as with protein and caffeine, there is no evidence to indicate that calcium intake recommendations should be adjusted according to salt intake.

Dietary requirements and bone mass. Because circulating calcium levels are so strictly controlled, blood calcium concentration is a poor indicator of calcium status. Chronic inadequate calcium intakes or poor intestinal absorption leads to reduced bone mass as PTH acts to maintain homeostatic blood calcium at the expense of skeletal strength. Bone mineral content (BMC) and bone mineral density (BMD) are common measures of bone strength and fracture risk. BMC is measured in grams, the amount of bone mineral at the selected site (for example, whole skeleton, lumbar spine, hip, forearm) and BMD (g/cm²) are calculated as BMC divided by bone area in the region of interest. An adult is defined as osteoporotic by the World Health Organization if his or her BMD is more than 2.5 standard deviations below gender-specific normal young adult BMD. Osteoporosis and related spine, hip, and wrist fractures are major public health concerns.

Recommended daily calcium intakes (measured in milligrams) increase from infancy through adolescence. The rate of calcium accretion relative to body size is greatest during infancy. Infants accrete approximately 140 mg of calcium per day during the first year of life. This need for calcium during the first year of life is reflected in the amount of milk consumed by human milk-fed infants. Although evidence indicates that feeding of formula results in greater bone mineral accretion than human milk feeding during the first year of life, there is no indication that this effect is beneficial either short-or long-term.

Calcium accretion continues in childhood, and maximal accretion occurs during puberty. Children of ages one to eight years accrete 60 to 200 mg of calcium per day. Peak calcium accretion occurs during puberty for both males (mean age 14.5 years) and females (mean age 12 years). Accordingly, calcium intake requirements are highest during adolescence.

Calcium retention and bone turnover decline after menarche in females, but the amount of calcium women need does not change because the percentage of calcium absorbed into the blood decreases. In males, bone mineral accretion occurs until mean age 17.5 years. Evidence from clinical trials indicates that calcium supplementation in children can increase BMD, but the effect occurs primarily among populations who usually have low calcium intake, is not apparent at all skeletal sites, and probably does not persist when supplementation is stopped. Apparently the benefit is short-term only.

Dietary calcium requirements decline for both males and females once adulthood is reached and remain constant throughout the reproductive years. Intestinal calcium absorption, however, also decreases with age. At the end of the reproductive years (approximately age fifty), bone-mass loss occurs in both males and females. Bone-mass loss is particularly pronounced in females during the first few years following menopause. The bone loss that occurs with the loss of estrogen at menopause cannot be reversed simply through increased calcium intake. Reductions in age-related bone loss through calcium supplementation have been demonstrated in postmenopausal women, but the effects vary by skeletal site, usual calcium intake, and postmenopausal age. Because of the reduction in intestinal calcium absorption with age in all individuals and the potential of increased calcium intake to offset bone loss due to estrogen depletion, increasing the amount of calcium in one's diet is recommended for all individuals over fifty years of age.

Maternal calcium requirements increase during the third trimester of pregnancy in accordance with fetal growth needs and to prepare for lactation, and the mother's intestinal calcium absorption efficiency increases in order to meet her increased need for calcium. If this need for more calcium is not met, the mother's skeleton will be depleted to meet the calcium demands of the fetus. Furthermore, calcium loss from the mother's skeleton occurs during lactation and cannot be prevented by calcium supplementation. However, evidence indicates that maternal bone density is recovered to prelactation levels within approximately six months after the recurrence of menses.

Toxicity. Calcium toxicity is uncommon but can occur if too much calcium is taken in through dietary supplements. In susceptible individuals, excess calcium intake can lead to the formation of kidney stones (renal calcium deposits); however, dietary calcium is not a common cause of kidney stones. Hypercalcemia from ingestion of large quantities of calcium supplements is rare but the resulting kidney problems and ramifications to cell function affect major tissues and organs. In the United States, the maximum daily calcium intake judged likely to pose no adverse health effects—Tolerable Upper Intake Level (UL)—is set at 2,500 mg per day for all ages beyond one year of age. There are insufficient data to determine a UL for calcium for infants less than one year of age.

Summary. Changes in dietary calcium requirements throughout the lifespan reflect concurrent alterations in growth rate, intestinal absorption efficiency, and reproductive and estrogen status. Because calcium plays vital roles in critical cell responses, plasma calcium levels are strictly homeostatically controlled at the expense of skeletal integrity, if necessary. Homeostatic control of circulating calcium involves PTH, vitamin D, and calcitonin. Appropriate lifestyle choices (for example, physical activity) and adequate calcium nutrition promote optimal bone-mass accretion during growth and young adulthood, possibly resulting in reduced current and future fracture risk. Dairy products and dietary supplements provide similarly adequate amounts of calcium to the body. Grains, fruits, and vegetables contain smaller amounts of calcium, and calcium absorption from foods high in oxalic acid or phytic acid is limited. Calcium-enriched products such as bread and fruit juice are becoming increasingly important sources of dietary calcium.

Bibliography

Abrams, S. A., K. O. O'Brien, and J. E. Stuff. "Changes in Calcium Kinetics Associated with Menarche." Journal of Clinical Endocrinology and Metabolism 81 (1996): 2017–2020.

Aloia, J. F., A. Vswani, J. K. Yeah, P. L. Ross, E. Flaster, and F. A. Dilmanian. "Calcium supplementation with and without Hormone Replacement Therapy to Prevent Post-menopausal Bone Loss." Annals of Internal Medicine 120 (1994): 97–103.

Barger-Lux, M. J., R. P. Heaney, and M. R. Stegman. "Effects of Moderate Caffeine Intake on the Calcium Economy of Premenopausal Women." American Journal of Clinical Nutrition 52 (1990): 722–725.

Bonjour, J. P., G. Theintz, F. Law, D. Slosman, and R. Rizzoli. "Peak Bone Mass." Osteoporosis International 1 (1994): S7–S13.

Dawson-Hughes, B., G. E. Dallal, E. A. Krall, L. Sadowski, N. Sahyoun, and S. Tannenbaum. "A Controlled Trial of the Effect of Calcium Supplementation on Bone Density in Postmenopausal Women." New England Journal of Medicine 323 (1990): 878–883.

Heaney, R. P. "Protein Intake and Bone Health: The Influence of Belief Systems on the Conduct of Nutritional Science." American Journal of Clinical Nutrition 73 (2001): 5–6.

Heaney, R. P., R. R. Recker, M. R. Stegman, and A. J. Moy. "Calcium Absorption in Women: Relationships to Calcium Intake, Estrogen Status, and Age." Journal of Bone and Mineral Research 4 (1989): 469–475.

Heaney, R. P., R. R. Recker, and C. M. Weaver. "Absorbability of Calcium Sources: The Limited Role of Solubility." Calcified Tissue International 46 (1990): 300–304.

Heaney, R. P., P. D. Saville, and R. R. Recker. "Calcium Absorption as a Function of Calcium Intake." Journal of Laboratory and Clinical Medicine 85 (1975): 881–890.

Heaney, R. P., and T. G. Skillman. "Calcium Metabolism in Normal Human Pregnancy." Journal of Clinical Endocrinology and Metabolism 33 (1971): 661–670.

Kalkwarf, H. J., B. L. Specker, D. C. Bianchi, J. Ranz, and M. Ho. "The Effect of Calcium Supplementation on Bone Density during Lactation and after Weaning." New England Journal of Medicine 337 (1997): 523–528.

Kurtz, T. W., H. A. Al-Bander, and R. C. Morris. "'Salt Sensitive' Essential Hypertension in Men." New England Journal of Medicine 317 (1987): 1043–1048.

Lu, P. W., J. N. Briody, G. D. Ogle, K. Morley, I. R. Humphries, J. Allen, R. Howman-Giles, D. Sillence, and C. T. Cowell. "Bone Mineral Density of Total Body, Spine, and Femoral Neck in Children and Young Adults: A Cross-Sectional and Longitudinal Study." Journal of Bone and Mineral Research 9 (1994): 1451–1458.

Martin, A. D., D. A. Bailey, and H. A. McKay. "Bone Mineral and Calcium Accretion during Puberty." American Journal of Clinical Nutrition 66 (1997): 611–615.

Prince, R. L., M. Smith, I. M. Dick, R. I. Price, P. G. Webb, N. K. Henderson, and M. M. Harris. "Prevention of Post-menopausal Osteoporosis: A Comparative Study of Exercise, Calcium Supplementation, and Hormone-Replacement Therapy." New England Journal of Medicine 325 (1991): 1189–1195.

Recker, R. R., K. M. Davies, S. M. Hinders, R. P. Heaney, M. R. Stegman, and D. B. Kimmel. "Bone Gain in Young Adult Women." Journal of the American Medical Association 268 (1992): 2403–2408.

Riis, B., K. Thomsen, and C. Christiansen. "Does Calcium Supplementation Prevent Postmenopausal Bone Loss?" New England Journal of Medicine 316: 173–177.

Specker, B. L., A. Beck, H. Kalkwarf, and M. Ho. "Randomized Trial of Varying Mineral Intake on Total Body Bone Mineral Accretion during the First Year of Life." Pediatrics 99 (1997): e12.

Wallace, B. A., and R. G. Cumming. "Systematic Review of Randomized Trials of the Effect of Exercise on Bone Mass in Pre- and Postmenopausal Women." Calcified Tissue International 67 (2000): 10–18.

World Health Organization. Assessment of Fracture Risk and Its Application to Screening for Postmenopausal Osteoporosis. Geneva, Switzerland: World Health Organization, 1994.

World Health Organization, Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride. Washington, D.C.: National Academy Press, 1997.

Wosje, K. S., and B. L. Specker. "Role of Calcium in Bone Health during Childhood." Nutrition Reviews 58 (2000): 253–268.

—Karen S. Wosje

A vital mineral needed for healthy teeth and bone growth and continued structure. Calcium is also important in the sequence of reactions needed in the clotting the blood. See Minerals, Vitamins.

---

symbol: Ca; an alkaline-earth metal of group 2 of the IUPAC periodic table; relative atomic mass 40.08, atomic number 20; it occurs naturally only in an ionized (Ca²⁺) or combined state, and is a mixture of stable nuclides of relative mass 40 (96.97 atom percent) and 44 (2.06 atom percent) with small proportions of nuclides of relative mass 43, 46, and 48. Calcium is the fifth most abundant element of the Earth's crust and is an essential component of all living material. It occurs in bone, shell, and teeth and low concentrations of ionic calcium play many important roles in the regulation of diverse cellular processes. The most abundant mineral in the human body, most of it is in the skeleton. It has especially important functions in bone, in the control of nervous, muscle, and other excitable tissue, and as a second messenger and regulator of enzyme activity. Calcium homeostasis depends on the action of: (1) parathyroid hormone, which increases tubular reabsorption of calcium, and releases calcium from bone, thereby having overall a hypercalcemic action; (2) vitamin D (calcitriol), which causes absorption of calcium from the gut and its release from bone, and also therefore has a hypercalcemic action; and (3) calcitonin, which reduces calcium resorption from bone. The range of plasma calcium in normal human adults is 2.2 — 2.6 mmol L^-1. See also hypercalcemia, hypocalcemia.

Previous:	calcitriol, calcitonin receptor, calcitonin gene-related peptide receptor
Next:	calcium channel, calcium ion, calcium phosphate-mediated transfection

A chemical element, atomic number 20, atomic weight 40.08, symbol Ca. Calcium is the most abundant mineral in the body. In combination with phosphorus it forms calcium phosphate, the dense, hard material of the bones and teeth. It is an important cation in intra- and extracellular fluid and is essential to the normal clotting of blood, the maintenance of a normal heartbeat, and the initiation of neuromuscular and metabolic activities.
Within the body fluids calcium exists in three forms. Protein-bound calcium accounts for about 47% of the calcium in plasma; most of it in this form is bound to albumin. Another 47% of plasma calcium is ionized. About 6% is complexed with phosphate, citrate and other anions.
Ionized calcium is physiologically active. One of its most important physiological functions is control of the permeability of cell membranes. Parathyroid hormone, which causes transfer of exchangeable calcium from bone into the bloodstream, and calcitriol maintain calcium homeostasis by preventing either calcium deficit or excess.

• c. arsenate — used extensively as a spray in orchards, constituting a poison hazard for livestock.
• avian c. poisoning — excess calcium in the avian diet, especially in diets low in phosphorus causes nephrosis, visceral gout and urolithiasis.
• c. balance — the balance between calcium intake and losses in feces and urine.
• c. borogluconate — see borogluconate.
• c. carbonate — an insoluble salt occurring naturally in bone, shells and chalk. A common form of supplementary calcium in dogs and cats on meat-based diets, used because of its high concentration of calcium (40%) and absence of phosphorus.
• c. challenge test — an intravenous infusion of calcium will cause increased levels of gastrin in dogs with a gastrinoma. Often used in combination with a secretin test.
• c. channels — see channel.
• c. chloride — a salt used in solution to restore electrolyte balance, to treat hypocalcemia and as an antidote to magnesium poisoning. Is highly irritant and has been discarded generally in favor of less irritating substances, e.g. calcium borogluconate.
• c. cyanamide — agricultural fertilizer capable of being toxic.
• c. cytosolic — see cytosol.
• diffusible c. — see calcium (above).
• c. edetate (Ca-EDTA) — calcium ethylenediamine tetra-acetic acid; the disodium and dipotassium salts are commonly used as anticoagulants in the preservation of blood samples for hematology. A chelating agent, used parenterally in the treatment of lead poisoning. See also edetate.
• excess c. — in all species may cause hypercalcitonism with decreased osteoclastic activity and skeletal remodeling. In dogs, disorders of enchondral ossification with curved radius and osteochondrosis have been demonstrated; secondary iron deficiency anemia occurs in piglets.
• c. fluoride — naturally occurring mineral. Called also fluorspar, fluorite.
• c. gel — contains high levels of calcium; given to cows as a drench or in the feed as a prophylaxis against milk fever.
• c. gluconate — a calcium replenisher and antidote to fluoride or oxalate poisoning.
• c. gout — see calcinosis circumscripta.
• c. homeostasis — maintenance of normal calcium metabolism by the combined effects of adequate alimentary intake, renal excretion, parathyroid hormone involvement, 1,25 dihydroxycholecalciferol (or calcitriol) and calcitonin, plasma protein binding and deposition in tissues.
• c. hydroxide — an astringent compound used topically in solution or lotions; in dentistry used to encourage deposition of secondary dentine. Called also slaked lime. In solution, called lime water.
• idiopathic c. phosphate deposition — thought to be inherited as an autosomal dominant trait in Great Danes commencing in puppies about 5 weeks old, characterized by incoordination with deformity and displacement of the 7th cervical vertebra and mineral deposits in the intervertebral joints, in serous and synovial membranes and mineralization in most other tissues.
• c. lactate — used for supplementing the diet with calcium; contains 18% calcium. As calcium sodium lactate, containing 8% calcium, it is more soluble and can be used in drinking water.
• c. levulinate — a calcium compound used parenterally in the treatment of hypocalcemia; contains 14.8% calcium.
• c. mandelate — administered orally and used as a urinary antiseptic.
• c. nitrate — used as an additive during cheese making to control fermentation. Whey from this cheese may cause nitrate poisoning in pigs.
• nondiffusible c. — protein-bound fractions of plasma calcium.
• c. nutritional deficiency — nutritional deficiency of calcium is rarely primary except in carnivores on an all-meat diet. Secondary deficiency is usually the result of diets having too high a content of phosphorus. The outcome of either deficiency may be nutritional hyperparathyroidism, rickets, osteomalacia, osteodystrophy in horse and pigs, and degenerative arthropathy of cattle, depending on the species, age of the animal and availability of vitamin D. Hypocalcemia may not occur because of the activity of parathyroid hormone, but classical tetany and recumbency can occur if the deficiency is prolonged or if they are precipitated by some other factor.
• c. oxalate — a compound occurring in the urine in crystals and in certain calculi. See also oxalate urolith.
• c. oxide — alkaline and capable of causing gastroenteritis. There is a high concentration in basic slag and this may contribute to that poisoning.
• c. pantothenate — a calcium salt of the dextrorotatory isomer of pantothenic acid; used as a growth-promoting vitamin.
• c. phosphate — one of three salts containing calcium and the phosphate radical: dibasic and tribasic calcium phosphate are used as sources of calcium; monobasic calcium phosphate is used in fertilizer and as a calcium and phosphorus supplement. An important constituent of uroliths.
• c. : phosphorus ratio — the ratio of calcium to phosphorus in the diet, 1 : 1 to 1 : 2 is usually considered to be adequate for proper calcium nutritional status in most animal species. Diets outside this range are likely to cause osteodystrophies. Animals grazing phosphorus-deficient pasture, and those being intensively fed on grain rations which have an abnormally high phosphorus content, are the principal subjects. Horses on heavy grain diets and dogs and cats on meat diets without calcium supplementation are also targets for the disease.
• c. polycarbophil — a hydrophilic agent used as a bulk laxative in the treatment of constipation and diarrhea.
• c. polysulfide — see lime-sulfur.
• c. propionate — see propionic acid.
• protein bound c. — biologically inert fraction of plasma calcium; most is bound to albumin and globulins with a small fraction complexed to organic and inorganic acids.
• c. silicophosphate — crystals of this mineral are thought to contribute physically to the gastroenteritis caused by basic slag poisoning.
• c. sulfate — the main component of plaster of Paris; also used as a dietary source of calcium and inorganic sulfate sulfur.
• c. sulfide, c. polysulfide — lime-sulfur.
• c. supplements — include calcium carbonate, gluconate, lactate and phosphate; bone flour, bone meal, ground limestone, chalk.
• c. tungstate screens — cards coated with calcium tungstate crystals are used to sandwich film in a light-tight cassette. They fluoresce when exposed to x-rays and, together with the beam, affect the film emulsion. They reduce the exposure factor required.
• urinary c. — calciuria.

(kal′sē-əm)
n
Ca

A basic element, with an atomic weight of 40.07, found in nearly all organized tissues. Essential for mineralization of bone and teeth. The normal level of calcium in the blood is 9 to 11.5 mg/100 ml. A deficiency of calcium in the diet or in use may lead to rickets or osteoporosis. Overexcretion in hyperparathyroidism leads to osteoporotic manifestations. See also factor IV.

For a list of words related to calcium, see:

• Pure metals
• Elements - calcium: Ca; atomic number 20, atomicweight 40

---

See words rhyming with "calcium."

  See crossword solutions for the clue Calcium.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - calcium, kalk

Nederlands (Dutch)
calcium

Français (French)
n. - calcium

Deutsch (German)
n. - (chem.) Kalzium

Ελληνική (Greek)
n. - (χημ.) ασβέστιο

Italiano (Italian)
calcio

Português (Portuguese)
n. - cálcio (m) (Quím.)

Русский (Russian)
кальций

Español (Spanish)
n. - calcio

Svenska (Swedish)
n. - kalcium

中文（简体）(Chinese (Simplified))
钙

中文（繁體）(Chinese (Traditional))
n. - 鈣

한국어 (Korean)
n. - 금속 원소 칼슘

日本語 (Japanese)
n. - カルシウム

العربيه (Arabic)
‏(الاسم) الكلسيوم‏

עברית (Hebrew)
n. - ‮סידן‬

If you are unable to view some languages clearly, click here.

To select your translation preferences click here.