calcium

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.]

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.

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.

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.

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.

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.

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
• Calcium Carbonate, Cholecalciferol Oral tablet
• Calcium Carbonate, Vitamin D Chewable tablet
• Calcium Citrate, Cholecalciferol Oral tablet
• Calcium Citrate, Cholecalciferol Soft chew
• Calcium Stearate, Cholecalciferol Oral tablet
• Calcium, Cholecalciferol Oral tablet

Español:
• 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
• Calcio; Colecalciferol, Tableta oral

Calcium Carbonate, Vitamin D Oral tablet

What is this medicine?

CALCIUM; VITAMIN 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?

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.

Description

As the most plentiful mineral in the body, calcium plays a key role in the development and maintenance of bones and teeth. Calcium enables the contraction of muscles, including the function of the body's most important muscle, the heart. It is also essential for normal blood clotting, proper nerve impulse transmission, and the appropriate support of connective tissue.

Almost every segment of the population—women, children, teenagers, men, unborn babies, and the elderly—benefit from calcium in their daily diet. The mineral is an important dietary supplement for those who are undergoing significant periods of bone growth, such as in childhood, during pregnancy, and while breast-feeding.

Calcium is an effective weapon for the aging population as they combat osteoporosis. A condition that simply means "porous bones," osteoporosis attacks bones when they are their most vulnerable. As the body ages, bones lose more calcium, and it becomes vital to supplement the diet with calcium in order to encourage bone growth and prevent or slow down the process of osteoporosis.

General Use

While the body relies on the presence of calcium for many of its everyday functions, the number of reasons why the mineral should be supplemented in the diet are numerous. Calcium is beneficial to everyone, but re-search has shown that women may benefit more than others. A study in the October 1999 issue of the journal Obstetrics & Gynecology found that pregnant women who do not get enough calcium in their diet can increase the bone mineral content of their fetus by about 15% by taking 1,300 mg of a calcium supplement per day during their second and third trimesters. For those women who already consume enough calcium, the additional supplements do not have this effect. Additional research shows that calcium deficiencies lead to preeclampsia during pregnancy, causing high blood pressure, swelling, and weight gain greater than 1 lb (0.5 kg) per day. The risk of preeclampsia developing lowers by 45–75% for women who receive calcium supplementation.

Premenstrual syndrome (PMS) is another condition women face that may be alleviated by the use of calcium supplements. Researchers at the National Institute of Mental Health (NIMH) concluded that those women who took 1,200 mg of calcium per day reduced their overall PMS symptoms by more than 50%. In the study, calcium supple-mentation led to the reduction of psychological PMS symptoms (such as mood swings) by 45%, food cravings by 54%, and bloating and water retention by 36%.

A 1999 study reported that researchers have found that increasing the amount of daily calcium consumed by women may reduce their risk of stroke. Those women in the Nurses' Health Study who took more than 400 mg of calcium daily were at the lowest risk for a stroke, while those who consumed more than 600 mg each day did not have an increased benefit. Researchers believe that the risk of stroke is reduced by calcium from decreased cholesterol levels, or by stopping the formation of blood clots that cause strokes.

For elderly postmenopausal women, the prevention of osteoporosis becomes critical. In order to maintain bone mass during this time, a study conducted in 1999 concluded that a low-dose hormone replacement therapy (HRT) combined with calcium and vitamin D supple-mentation is an effective therapeutic option for prevention of osteoporosis. Estriol, which is used in HRT, appears to be helpful in controlling menopausal symptoms. Results from research regarding this use of estriol on bone density have been contradictory, according to the Alternative Medicine Review, with the results showing the most effectiveness coming from Japanese studies.

Calcium alone is frequently prescribed with estrogen at the beginning of menopause to treat or prevent osteoporosis. This therapy is recommended to guard against the increased loss of calcium in the bones due to increasing age. As bones lose more calcium they become dense and brittle, and more vulnerable to the attack of osteoporosis. This condition is most common in people over 70, and in women after menopause, where it may increase the risk of broken hips, ribs, and pelvis, and the weakening of other bones. Increased physical exercise is also important for bone strengthening.

On the other hand, although calcium supplementation is useful in lowering the risk of osteoporosis in Western women, more research is needed to determine why the rates of osteoporosis are low in some Eastern societies with low-calcium diets. There is evidence that osteoporosis, like coronary artery disease, is primarily a problem in Western societies. In addition, accumulating evidence that a diet high in fruits and vegetables helps to prevent fractures suggests that the level of calcium in the diet is not the only nutritional factor involved in osteoporosis.

Calcium has been shown to be beneficial to the colon. Among those people taking calcium supplements, research points to a modest reduction in the recurrence of polyps in their colons. Colon polyps are benign tumors that often turn cancerous. Researchers think that calcium binds to carcinogens, preventing abnormal cell growth.

Stemming from its active role in building bone density throughout the body, calcium may prove particularly beneficial for strengthening of the jawbone. Dental researchers at the State University of New York at Buffalo report that calcium supplementation may prevent periodontal disease as it builds a strong jawbone. Periodontal, or gum, disease is an infection caused by bacteria that deposits in pockets between the teeth and gums, and is the leading cause of tooth loss in the United States. As the infection progresses, the jawbone that holds a tooth in place is eventually destroyed, causing the tooth to loosen and fall out. The researchers contend that calcium's overall bone-building role would equal a stronger jawbone that would better fight off gum disease.

While supplements of calcium can be found in many forms, research has shown a promising benefit if it is obtained from dairy foods, rather than supplements or leafy greens—calcium in the form of dairy may actually prevent weight gain. Those in the study who consumed at least 1,000 mg of calcium a day (equaling about 3 cups, or 750 ml of skim milk), gained 6–7 lb (2.7–3.2 kg) less over two years than those with low-calcium diets. Researchers of Purdue University speculate that calcium probably prevents weight gain by increasing the breakdown of body fat and decreasing its formation. It is important to note, however, that dairy products should be consumed in moderation, as other research conducted has indicated that dairy products are not necessarily a good source of absorbable calcium. In addition, other studies indicate that women are often reluctant to increase their intake of dairy products because they dislike milk, suffer from lactose intolerance, or fear that they will gain too much weight.

Calcium is proving essential to those children around the world who are stricken by rickets. Rickets is a deficiency condition in children that affects developing cartilage and newly formed bone throughout the body, causing severe deformities. Often thought to be a result of the inadequate intake of vitamin D from dietary sources or lack of exposure to sunlight, research reported in 2000 has found that children with rickets respond well to calcium supplementation. While rickets is still rare in most developed countries, it is becoming more common in the United States due to lower milk consumption by children; and it remains a problem in many other parts of the world. Researchers conclude that effective treatment for the condition is calcium supplementation alone, or in combination with vitamin D. Osteomalacia, or the adult form of rickets, also responds to calcium supplementation.

Evidence is accumulating in the United States that women are not the only group at risk for insufficient dietary levels of calcium. Children and adolescents are also at risk, according to a 2001 report from the National Institutes of Health. Researchers found that "only 13.5% of girls and 36.3% of boys ages 12 to 19 in the United States get the recommended daily amount (RDA) of calcium, placing them at serious risk for osteoporosis and other bone diseases" in their adult years. The report listed increased consumption of soft drinks and decreased consumption of milk as contributing to the problem.

Preparations

Calcium may be supplemented in the diet in a variety of ways. Numerous foods are rich in calcium, including dairy products (such as milk, yogurt, and cheese) and leafy green vegetables like turnip greens, broccoli, kale, and collards. Canned salmon, sardines, shrimp, and tofu are also high in calcium. More foods are being fortified with calcium, making it easier to ensure the proper amount of the mineral is consumed. Calcium-fortified foods range from cranberry juice cocktail, cereal and waffles, to orange juice and flour. With almost every segment of the population consuming too little calcium, researchers recommend calcium-fortified foods to increase daily calcium intake.

While the types of food calcium may be obtained from continues to increase, most people still lack enough of the essential mineral. For those who are not getting enough calcium from foods, supplements are an acceptable alternative. The chemical form of calcium supplements come in five varieties: carbonate, citrate, lactate, phosphate, chelate, and citrate malate. The supplements are available as tablets, syrup, or suspension form. Calcium supplements should be stored at room temperature and away from moisture and sunlight. It should not be stored in the bathroom, and the liquid forms should not be frozen.

Experts state that calcium is best absorbed from the citrate malate form, or the type of calcium found in some juices, but they recommend calcium carbonate for the overall amount of calcium it offers and its affordability. Calcium carbonate can be found in antacids, and it is absorbed better when taken with meals. Food slows down the time it takes substances to travel through the gut, giving the calcium more time to be absorbed. Absorption is key for the proper functioning of calcium. Sufficient levels of vitamin D and hydrochloric acid in the stomach, and the presence of other minerals, such as magnesium and phosphorous are essential for quick absorption.

The body may also be better able to absorb calcium when taken along with ingredients extracted from chicory root. Research indicates that Raftilin inulin and Raftilose oligofructose, both extracts from chicory root, are dietary fibers that are not digested in the stomach or the small intestine. Instead, they are fermented by Bifidobacteria in the colon—beneficially leading to increased calcium absorption throughout the body, with emphasis on bone tissue. Additionally, Oligofructose improves the texture and mouthfeel while improving taste and fruit flavors in low-fat yogurts. Inulin is used for fat replacement and fiber enrichment of reduced-fat and fat-free sour cream and whipped topping.

There are many ways to ensure calcium is part of a daily diet, but it is important that the recommended daily allowance (RDA), or appropriate dosage of the mineral be followed. The RDA of calcium for adults is 800 mg; pregnant women and young adults should be certain their intake equals 1,200 mg per day. Adults over 50 should increase their intake to 1,000 mg per day with supplements that include vitamin D.

Calcium supplements may be taken with a large glass of water during or after a meal. Tablets in chewable form must be chewed thoroughly before swallowing, and effervescent tablets should be diluted in cold water or juice before taking. It is recommended that other medications be taken two hours after any calcium supplement. The simultaneous intake of calcium may interfere with the absorption of other drugs. Do not take more than 500 mg of calcium at one time for the best absorption of the mineral.

Precautions

When adding calcium supplements to the diet, it is recommended that it not be taken within one to two hours of eating bran, or whole grain cereals or breads. Large amounts of alcohol or caffeine containing beverages or tobacco should be avoided. Large amounts of calcium, phosphates, magnesium, or vitamin D in medication or dietary supplements should not be taken unless directed by a physician. Those with diarrhea, stomach trouble, parathyroid disease, sarcoidosis, or kidney stones should consult with their physician before taking calcium.

Side Effects

Calcium is typically well tolerated by those who add it to their diets, but if the mineral is taken in high levels it can cause several side effects, including: nausea, vomiting, loss of appetite, constipation, stomach pain, thirst, dry mouth, increased urination, and weakness. While these side effects are rare, it is even more unlikely to experience the life-threatening symptoms of an irregular or very slow heart beat. If these dangerous symptoms appear while taking calcium, use of the mineral should be discontinued and emergency treatment should be sought. An overdose of a calcium supplement may lead to confusion, irregular heartbeat, depression, bone pain, or coma.

Interactions

It is important that all over-the-counter (OTC) or prescription medications are reviewed with a physician before beginning calcium supplement.

According to the Complete Guide to Prescription & Nonprescription Drugs, the following are some of the drugs that may cause possible interactions if taken with calcium:

• alendronate
• anticoagulants
• calcitonin
• calcium-containing medicines
• chlorpromazine
• oral contraceptives
• corticosteroids
• digitalis preparations
• diuretics, thiazide
• estrogens
• etidronate
• iron supplements
• meperidine
• mexiletine
• nalidixic acid
• nicardipine
• nimodipine
• oxyphenbutazone
• para-aminosalicyclic acid (PAS)
• penicillins
• pentobarbital
• phenylbutazone
• phenytoin
• pseudoephedrine
• quinidine
• salicylates

Resources

Books

The Editors of Time-Life Books. "Essential Vitamins and Minerals." In The Medical Advisor: The Complete Guide to Alternative & Conventional Treatments. Richmond, VA: Time-Life Inc., 1996.

Griffith, H. Winter. "Calcium Supplements." In Complete Guide to Prescription & Nonprescription Drugs, 1999 Edition. New York: The Berkley Publishing Group, 1998.

Periodicals

"Calcium May Help Prevent Colon Polyps." Environmental Nutrition 22, no. 2 (February 1999): 1.

"Calcium May Help Prevent Gum Trouble." Tufts University Health & Nutrition Letter 17, no. 5 (July 1999): 6.

"Calcium May Reduce Stroke Risk in Women." Stroke (September 1999).

"The Four Supplements You Can't Live Without." Prevention 51, no. 12 (December 1999): 1.

Gulliver, Pauline, and Caroline C. Horwath. "Assessing Women's Perceived Benefits, Barriers, and Stage of Change for Meeting Milk Product Consumption Recommendations. " Journal of the American Dietetic Association 101 (November 2001): 1354–1357.

Head, Kathleen A., N.D. "Estriol: Safety and Efficacy." Alternative Medicine Review 3, no. 2 (April 1998). .

Hegsted, D. Mark. "Fractures, Calcium, and the Modern Diet." American Journal of Clinical Nutrition 74 (November 2001): 571.

Liebman, Bonnie. "Calcium Supplements: The Way to Go." Nutrition Action Healthletter 25, no. 3 (April 1998): 5.

Marion, Matt. "Health Bulletin." Men's Health 14, no. 10 (December 1999): 32.

"Using Calcium to Combat PMS Symptoms." Medical Update 22, no. 5 (November 1998): 6.

Wallace, Phil. "NIH Says Calcium 'Crisis' is Affecting Young People." Food Chemical News 43 (December 17, 2001): 27.

Organizations

Food and Drug Administration, Office of Consumer Affairs, HFE–88, Rockville, MD 20857.

[Article by: Beth Kapes; Rebecca J. Frey, PhD]

For more information on calcium, visit Britannica.com.

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 (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

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—Karen S. Wosje

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.

This article is about the metallic element. For the place, see Calcium, New York.

potassium ← calcium → scandium Mg ↑ Ca ↓ Sr 20Ca Periodic table
Appearance
Dull gray, silver
General properties
Name, symbol, number	calcium, Ca, 20
Element category	alkaline earth metal
Group, period, block	2, 4, s
Standard atomic weight	40.078(4) g·mol−1
Electron configuration	[Ar] 4s2
Electrons per shell	2, 8, 8, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	1.55 g·cm−3
Liquid density at m.p.	1.378 g·cm−3
Melting point	1115 K, 842 °C, 1548 °F
Boiling point	1757 K, 1484 °C, 2703 °F
Heat of fusion	8.54 kJ·mol−1
Heat of vaporization	154.7 kJ·mol−1
Specific heat capacity	(25 °C) 25.929 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k at T/K 864 956 1071 1227 1443 1755
Atomic properties
Oxidation states	2 (strongly basic oxide)
Electronegativity	1.00 (Pauling scale)
Ionization energies (more)	1st: 589.8 kJ·mol−1
	2nd: 1145.4 kJ·mol−1
	3rd: 4912.4 kJ·mol−1
Atomic radius	197 pm
Covalent radius	176±10 pm
Van der Waals radius	231 pm
Miscellanea
Crystal structure	face-centered cubic
Magnetic ordering	diamagnetic
Electrical resistivity	(20 °C) 33.6 nΩ·m
Thermal conductivity	(300 K) 201 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
Young's modulus	20 GPa
Shear modulus	7.4 GPa
Bulk modulus	17 GPa
Poisson ratio	0.31
Mohs hardness	1.75
Brinell hardness	167 MPa
CAS registry number	7440-70-2
Most stable isotopes
Main article: Isotopes of calcium
iso NA half-life DM DE (MeV) DP 40Ca 96.941% 40Ca is stable with 20 neutrons 41Ca trace 1.03×105 y ε - 41K 42Ca 0.647% 42Ca is stable with 22 neutrons 43Ca 0.135% 43Ca is stable with 23 neutrons 44Ca 2.086% 44Ca is stable with 24 neutrons 45Ca syn 162.7 d β− 0.258 45Sc 46Ca 0.004% >2.8×1015 y β−β−  ? 46Ti 47Ca syn 4.536 d β− 0.694, 1.99 47Sc γ 1.297 - 48Ca 0.187% >4×1019 y β−β−  ? 48Ti
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Calcium (pronounced /ˈkælsiəm/, KAL-see-əm) is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. 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.^[1]

Calcium is essential for living organisms, particularly 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 bones and shells, calcium is the most abundant metal by mass in many animals.

Contents 1 Notable characteristics 2 Occurrence 3 Applications 3.1 Calcium compounds 3.2 H and K lines 4 History 5 Compounds 6 Isotopes 7 Nutrition 7.1 Dietary calcium supplements 7.2 Prevention of fractures due to osteoporosis 7.3 Possible cancer prevention 7.4 Overdose 8 See also 9 Notes 10 References 11 External links

Notable characteristics

Flame test. Orange color originates from calcium.

Chemically 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.^[2] Once produced, it rapidly forms a gray-white oxide and nitride coating when exposed to air. It is somewhat difficult to ignite, unlike magnesium, but when lit, the metal burns in air with a brilliant high-intensity red light. Calcium metal reacts with water, evolving hydrogen gas at a rate rapid enough to be noticeable, but not fast enough at room temperature to generate much heat. 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 slowness of the calcium-water reaction results from the metal being partly protected by insoluble white calcium hydroxide. In water solutions of acids where the salt is water soluble, calcium reacts vigorously.

Calcium, with a specific mass of 1.55 g/cm³, is the lightest of the alkali earth metals; magnesium (1.74) and beryllium (1.84) are heavier although they are lighter in atomic mass. From strontium on, the alkali earth metals get heavier along with the atomic mass.

Calcium has a higher resistivity than copper or aluminium. Yet, weight for weight, allowing for 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. Many calcium salts are not soluble in water. When in solution, the calcium ion to the human taste varies remarkably, 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.^[3] 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 a common cellular ionic messenger with many functions, and serves also as a structural element in bone. It is the relatively high atomic-numbered calcium in the skeleton which causes bone to be radio-opaque. Of the human body's solid components after drying (as for example, after cremation), about a third of the total mass is the approximately one kilogram of calcium which composes the average skeleton (the remainder being mostly phosphorus and oxygen).

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: plagioclase, amphiboles, pyroxenes and garnets.

See also Calcium minerals.

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.
• in the making of cheese, where calcium ions influence the activity of rennin in bringing about the coagulation of milk.

Calcium compounds

• Calcium carbonate (CaCO₃) 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 hydroxide solution (Ca(OH)₂) (also known as limewater) is used to detect the presence of carbon dioxide by being bubbled through a solution. It turns cloudy where CO₂ is present.
• Calcium arsenate (Ca₃(AsO₄)₂) is used in insecticides.
• Calcium carbide (CaC₂) is used: to make acetylene gas (for use in acetylene torches for welding) and in the manufacturing of plastics.
• Calcium chloride (CaCl₂) 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(C₆H₁₁NHSO₃)₂) was used as a sweetening agent but is no longer permitted for use because of suspected cancer-causing properties.
• Calcium gluconate (Ca(C₆H₁₁O₇)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 algaecide and fungicide.
• Calcium permanganate (Ca(MnO₄)₂) is used in liquid rocket propellant, textile production, as a water sterilizing agent and in dental procedures.
• Calcium phosphate (Ca₃(PO₄)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 (Ca₃P₂) is used in fireworks, rodenticide, torpedoes and flares.
• Calcium stearate (Ca(C₁₈H₃₅O₂)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 (CaSO₄·2H₂O) is used as common blackboard chalk, as well as, in its hemihydrate form better known as Plaster of Paris.
• Calcium tungstate (CaWO₄) is used in luminous paints, fluorescent lights and in X-ray studies.
• Hydroxylapatite (Ca₅(PO₄)₃(OH), but is usually written Ca₁₀(PO₄)₆(OH)₂) makes up seventy percent of bone. Also carbonated-calcium deficient hydroxylapatite is the main mineral of which dental enamel and dentin are comprised.

H and K lines

In the visible portion of the spectrum of many stars, including the Sun, strong absorption lines of singly-ionized calcium are shown. 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.^[4]

History

Calcium (Latin word calcis meaning "lime") 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 sulphate), 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. 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.

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 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 and 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.

Isotopes

Main article: 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.

The most abundant isotope, ⁴⁰Ca, has a nucleus of 20 protons and 20 neutrons. This is the heaviest stable isotope of any element which 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]}

Nutrition

Main articles: calcium in biology and calcium metabolism

Recommended Adequate Intake by the IOM for Calcium:^[5]

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 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 ninety-nine percent of the body's calcium is stored in the bones and teeth.^[6] 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.^[7] 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.^[8][9][10] 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, particularly 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. Fortunately, many 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; figs; quinoa; amaranth; collard greens; okra; rutabaga; broccoli; dandelion leaves; kale; and fortified products such as orange juice and soy milk. Research has found an association between diets high in animal protein and increased urinary calcium loss from the bones^[11][12][13]. A diet high in fruit, vegetables and cereals was demonstrated to result in greater femoral bone mineral density in older men, in comparison to a range of other diets. Diets high in candy were found to result in lower bone density in both men and women ^[14]. An overlooked source of calcium is eggshell, which can be ground into a powder and mixed into food or a glass of water.^[15][16][17] Cultivated vegetables generally have less calcium than wild plants.^[18]

The calcium content of most foods can be found in the USDA National Nutrient Database.^[19]

Dietary calcium supplements

500 milligram calcium supplements made from calcium carbonate

Calcium supplements are used to prevent and to treat calcium deficiencies. Most experts recommend that supplements be taken with food and that no more than 600 mg should be taken at a time because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases.^[5] It is recommended to spread doses throughout the day. Recommended daily calcium intake for adults ranges from 1000 to 1500 mg. It is recommended to take supplements with food to aid in absorption.

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.^[20]

• The absorption of calcium from most food and commonly-used dietary supplements is very similar.^[21] This is contrary to what many calcium supplement manufacturers claim in their promotional materials.
• Milk is an excellent source of dietary calcium because it has a high concentration of calcium and the calcium in milk is excellently absorbed.^[21]
• Calcium carbonate is the most common and least expensive calcium supplement. It should be taken with food. It depends on low pH levels for proper absorption in the intestine.^[22] Some studies suggests that the absorption of calcium from calcium carbonate is similar to the absorption of calcium from milk.^[23][24] While most people digest calcium carbonate very well, some might develop gastrointestinal discomfort or gas. Taking magnesium with it can help to avoid constipation. Calcium carbonate is 40% elemental calcium. 1000 mg will provide 400 mg of calcium. However, supplement labels will usually indicate how much calcium is present in each serving, not how much calcium carbonate is present.
• Antacids, such as Tums, frequently contain calcium carbonate, and are a very commonly-used, inexpensive calcium supplement.
• Coral Calcium is a salt of calcium derived from fossilized coral reefs. Coral calcium is composed of calcium carbonate and trace minerals.
• Calcium citrate can be taken without food and is the supplement of choice for individuals with achlorhydria or who are taking histamine-2 blockers or proton-pump inhibitors.^[25] It is more easily digested and absorbed than calcium carbonate if taken on empty stomach 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 has similar absorption as calcium carbonate^[26], but is more expensive. Calcium lactate and calcium gluconate are less concentrated forms of calcium and are not practical oral supplements.^[25]
• Calcium chelates are synthetic calcium compounds, with calcium bound to an organic molecule, such as malate, aspartate, or fumarate. These forms of calcium may be better absorbed on an empty stomach. However, in general they are absorbed similarly to calcium carbonate and other common calcium supplements when taken with food.^[27] The 'chelate' mimics the action that natural food performs by keeping the calcium soluble in the intestine. Thus, on an empty stomach, in some individuals, chelates might theoretically be absorbed better.
• Microcrystalline hydroxyapatite (MH) is marketed as a calcium supplement, and has in some randomized trials been found to be more effective than calcium carbonate.
• Orange juice with calcium added is a good dietary source for persons who have lactose intolerance.

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 "going out on a limb" to suggest calcium supplements as a weight-limiting aid.^[28]

Prevention of fractures due to osteoporosis

Such studies often do not test calcium alone, but rather combinations of calcium and vitamin D. Randomized controlled trials found both positive^[29][30] and negative^{[31][32][33][34]} effects. The different results may be explained by doses of calcium and underlying rates of calcium supplementation in the control groups.^[35] However, it is clear that increasing the intake of calcium promotes deposition of calcium in the bones, where it is of more benefit in preventing the compression fractures resulting from the osteoporotic thinning of the dendritic web of the bodies of the vertebrae, than it is at preventing the more serious cortical bone fractures which happen at hip and wrist.

Possible cancer prevention

A meta-analysis^[30] by the international Cochrane Collaboration of two randomized controlled trials^[36][37] found that calcium "might contribute to a moderate degree to the prevention of adenomatous colonic polyps".

More recent studies were conflicting, and one which 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) ^[38].

• A randomized controlled trial found that 1000 mg of elemental calcium and 400 IU of vitamin D₃ had no effect on colorectal cancer^[39]
• A randomized controlled trial found that 1400–1500 mg supplemental calcium and 1100 IU vitamin D₃ reduced aggregated cancers with a relative risk of 0.402.^[40]
• An observational cohort study found that high calcium and vitamin D intake was associated with "lower risk of developing premenopausal breast cancer."^[41]

Overdose

Exceeding the recommended daily calcium intake for an extended period of time can result in hypercalcemia and calcium metabolism disorder, as well as kidney stones.

See also

• Calcium metabolism
• Calcium in biology
• Calcium compounds
• Disorders of calcium metabolism

Notes

1. ^ A. G. Dickson, C. Goyet (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. http://cdiac.esd.ornl.gov/ftp/cdiac74/chapter5.pdf. 
2. ^ Pauling, Linus (1970). General Chemistry. Dover Publications. p. 627. ISBN 0716701499. 
3. ^ M. G. Tordoff. "Calcium: Taste, Intake, and Appetite". Physiological Reviews 81 (4): 1567. http://physrev.physiology.org/cgi/content/full/81/4/1567. 
4. ^ Staff (1995). "H-K Project". Mount Wilson Observatory. http://www.mtwilson.edu/hk/. Retrieved 2006-08-10. 
5. ^ ^{a b} "Dietary Supplement Fact Sheet: Calcium". http://ods.od.nih.gov/factsheets/calcium.asp. 
6. ^ "Osteoporosis Prevention - Calcium Recommendations". http://www.nof.org/prevention/calcium2.htm. 
7. ^ 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 0309064031. 
8. ^ 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.". The New England journal of medicine 328 (12): 833–8. PMID 8441427. 
9. ^ 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. 
10. ^ Hall WD, Pettinger M, Oberman A, et al. (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. 
11. ^ Abelow BJ, Holford TR, and Insogna KL. "Cross-cultural association between dietary animal protein and hip fracture: a hypothesis." Calcif. Tissue Int. 50 (1992): 14-18
12. ^ Margen S, Chu J-Y, Kaufmann NA, et al. "Urinary calcium and calcium balance in young men as affected by level of protein and phosphorus intake." Journal of Nutrition. 111 (1981): 553-62
13. ^ Kerstetter JE and Allen LH. "Dietary protein increases urinary calcium." Journal of Nutrition 120 (1990): 134-6
14. ^ American Journal of Clinical Nutrition 2002;76(1): 245-252
15. ^ Anne Schaafsma, Gerard M Beelen (1999). "Eggshell powder, a comparable or better source of calcium than purified calcium carbonate: piglet studies" (abstract). 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. http://www3.interscience.wiley.com/cgi-bin/abstract/63003036/ABSTRACT. 
16. ^ 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. 
17. ^ 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. 
18. ^ "Original Wild Foods vs. Available Foods Today for Instinctos". http://www.beyondveg.com/nieft-k/instincto-guide/instincto-guide1e.shtml. 
19. ^ "USDA National Nutrient Database". http://www.nal.usda.gov/fnic/foodcomp/search. 
20. ^ Combs, G (2008). The Vitamins. Academic Press. p. 161. 
21. ^ ^{a b} Weaver, CM (2006). "Calcium". Present Knowledge in Nutrition, 9th Ed.. I. ILSI Press. p. 377. 
22. ^ Remington, Joseph (2005). Remington: The Science and Practice of Pharmacy. Lippincott Williams & Wilkins. pp. 1338. ISBN 0781746736. 
23. ^ Zhao, Y. et al.. "Calcium bioavailability of calcium carbonate fortified soy milk is equivalent to cow's milk in young women". J. Nutr. 135 (10): 2379. 
24. ^ Ligia Martini and Richard J Wood (2002). "Relative bioavailability of calcium-rich dietary sources in the elderly". American Journal of Clinical Nutrition 76 (6): 1345–1350. http://www.ajcn.org/cgi/content/abstract/76/6/1345. 
25. ^ ^{a b} Straub, D. A. (2007). "Calcium Supplementation in Clinical Practice: A Review of Forms, Doses, and Indications". Nutrition in Clinical Practice 22: 286. doi:10.1177/0115426507022003286. 
26. ^ Martin, Berdine R. (2002). "Calcium Absorption from Three Salts and CaSO₄-Fortified Bread in Premenopausal Women". Journal of Agricultural and Food Chemistry 50: 3874. doi:10.1021/jf020065g. 
27. ^ Weaver, Connie M. (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: 4974. doi:10.1021/jf0200422. 
28. ^ Anne Harding. "Calcium May Help With Weight Loss". http://www.rxalternativemedicine.com/headlines_news.php#headline77. Retrieved 2007-07-10. 
29. ^ 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. 
30. ^ ^{a b} Weingarten MA, Zalmanovici A, Yaphe J (2005). "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. 
31. ^ Jackson RD, LaCroix AZ, Gass M, et al. (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. 
32. ^ Grant AM, Avenell A, Campbell MK, et al. (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. 
33. ^ Porthouse J, Cockayne S, King C, et al. (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. PMID 15860827. 
34. ^ 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. 
35. ^ 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. http://www.acpjc.org/Content/145/1/issue/ACPJC-2006-145-1-004.htm. 
36. ^ Baron JA, Beach M, Mandel JS, et al. (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. 
37. ^ 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. 
38. ^ 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." (Free full text). The American journal of clinical nutrition 85 (6): 1586–91. PMID 17556697. http://www.ajcn.org/cgi/pmidlookup?view=long&pmid=17556697. 
39. ^ Wactawski-Wende J, Kotchen JM, Anderson GL, et al. (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. 
40. ^ 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. 
41. ^ 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. 

References

• Rebecca J. Donatelle. Health, The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.

External links

Wikimedia Commons has media related to: Calcium

Look up calcium in Wiktionary, the free dictionary.

• WebElements.com — Calcium
• USDA National Nutrient Database, Calcium content of selected foods
• UK Food Standards Agency: Calcium

v • d • e Periodic table
H																															He
Li	Be																									B	C	N	O	F	Ne
Na	Mg																									Al	Si	P	S	Cl	Ar
K	Ca	Sc															Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr	Y															Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Cs	Ba	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Uub	Uut	Uuq	Uup	Uuh	Uus	Uuo
Alkali metals Alkaline earth metals Lanthanoids Actinoids Transition metals Other metals Metalloids Other nonmetals Halogens Noble gases

v • d • e   Calcium compounds CaB6 · CaBr2 · CaC2 · CaCN2 · CaCO3 · CaC2O4 · CaCl · CaCl2 · Ca(ClO)2 · Ca(ClO3)2 · CaCrO4 · CaF2 · CaH2 · Ca(HCO3)2 · CaH2S2O6 · CaI2 · Ca(IO3)2 · Ca(MnO4)2 · Ca(NO3)2 · CaO · CaO2 · Ca(OH)2 · CaS · CaSO3 · CaSO4 · CaSi2 · CaTiO3 · Ca2P2O7 · Ca2SiO4 · Ca3(AsO4)2 · Ca3(BO3)2 · Ca3(C6H5O7)2 · Ca3N2 · Ca3P2 · Ca3(PO4)2

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

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