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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.
| Property | Value |
|---|---|
Atomic number | 20 |
Atomic weight | 40.08 |
Isotopes (stable) | 40, 42, 43, 44, 46, 48 |
Atomic volume, cm3/g-atom | 25.9 |
Crystal form | Face-centered cubic |
Valence | 2+ |
Ionic radius, nm | 0.099 |
Electron configuration | 2882 |
Boiling point, °C | 1487(?) |
Melting point, °C | 810(?) |
Density, g/cm3 at 20°C | 1.55 |
Latent heat of vaporization at boiling point, kilojoules/g-atom | 399 |
Occurrence of calcium is very widespread; it is found in every major land area of the world. This element is essential to plant and animal life, and is present in bones, teeth, eggshell, coral, and many soils. Calcium chloride is present in sea water to the extent of 0.15%.
Calcium metal is prepared industrially by the electrolysis of molten calcium chloride. Calcium chloride is obtained either by treatment of a carbonate ore with hydrochloric acid or as a waste product from the Solvay carbonate process. The pure metal may be machined in a lathe, threaded, sawed, extruded, drawn into wire, pressed, and hammered into plates.
In air, calcium forms a thin film of oxide and nitride, which protects it from further attack. At elevated temperatures, it burns in air to form largely the nitride. The commercially produced metal reacts easily with water and acids, yielding hydrogen that contains noticeable amounts of ammonia and hydrocarbons as impurities.
The metal is employed as an alloying agent for aluminum-bearing metal, as an aid in removing bismuth from lead, and as a controller for graphitic carbon in cast iron. It is also used as a deoxidizer in the manufacture of many steels, as a reducing agent in preparation of such metals as chromium, thorium, zirconium, and uranium, and as a separating material for gaseous mixtures of nitrogen and argon.
Calcium oxide, CaO, is made by the thermal decomposition of carbonate minerals in tall kilns using a continuous-feed process. The oxide is used in high-intensity arc lights (limelights) because of its unusual spectral features and as an industrial dehydrating agent. The metallurgical industry makes wide use of the oxide during the reduction of ferrous alloys.
Calcium hydroxide, Ca(OH)2, is used in many applications where hydroxide ion is needed. During the slaking process for producing calcium hydroxide, the volume of the slaked lime [Ca(OH)2] produced expands to twice that of quicklime (CaO), and because of this, it can be used for the splitting of rock or wood. Slaked lime is an excellent absorbent for carbon dioxide to produce the very insoluble carbonate.
Calcium silicide, CaSi, an electric-furnace product made from lime, silica, and a carbonaceous reducing agent, is useful as a steel deoxidizer. Calcium carbide, CaC2, is produced by heating a mixture of lime and carbon to 5432°F (3000°C) in an electric furnace. The compound is an acetylide which yields acetylene upon hydrolysis. Acetylene is the starting material for a great number of chemicals important in the organic chemicals industry.
Pure calcium carbonate exists in two crystalline forms: calcite, the hexagonal form, which possesses the property of birefringence, and aragonite, the rhombohedral form. Naturally occurring carbonates are the most abundant of the calcium minerals. Iceland spar and calcite are essentially pure carbonate forms, whereas marble is a somewhat impure and much more compact variety which, because it may be given a high polish, is much in demand as a construction stone. Although calcium carbonate is quite insoluble in water, it has considerable solubility in water containing dissolved carbon dioxide, because in these solutions it dissolves to form the bicarbonate. This fact accounts for cave formation in which limestone deposits have been leached away by the acidic ground waters.
The halides of calcium include the phosphorescent fluoride, which is the most widely distributed calcium compound and which has important applications in spectroscopy. Calcium chloride has in the anhydrous form important deliquescent properties which make it useful as an industrial drying agent and as a dust quieter on roads. Calcium chloride hypochlorite (bleaching powder) is produced industrially by passing chlorine into slaked lime, and has been used as a bleaching agent and a water purifier. See also
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.
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®
Calcium; Vitamin D tablets
What are Calcium; Vitamin D tablets?
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
• diarrhea
• heart rhythm problems
• intestine obstruction
• kidney disease
• kidney stones
• liver disease
• parathyroid disease
• sarcoidosis
• stomach ulcer
• too much calcium or vitamin D in the blood or urine
• too much phosphate in the blood
• 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 this medicine be used?
Take calcium; vitamin D tablets by mouth. Follow the directions on the prescription or package label. Swallow the tablets with a full glass of water. Take with food or within 1 hour after a meal, unless your prescriber or health care professional tells you otherwise. Take your doses at regular intervals. Do not take more than the prescribed dose.
Contact your pediatrician or health care professional regarding the use of this medicine in children. Special care may be needed.
What if I miss a dose?
What drug(s) may interact with Calcium; Vitamin D?
Talk to your prescriber or other health care professional before taking any of these medicines:
• antacids
• multi-vitamin, multi-mineral supplements
• other medicines with calcium as an ingredient
• other medicines with vitamin D as an ingredient
Tell your prescriber or health care professional about all other medicines you are taking, including non-prescription medicines, nutritional supplements, or herbal products. Also tell your prescriber or health care professional if you are a frequent user of drinks with caffeine or alcohol, if you smoke, or if you use illegal drugs. These may affect the way your medicine works. Check with your health care professional before stopping or starting any of your medicines.
What should I watch for while taking Calcium; Vitamin D?
The absorption of calcium can be reduced if you take it with high-fiber foods, large amounts of alcohol, or drinks containing caffeine. Do not take calcium; vitamin D within 2 hours of any other medicines.
Do not use bonemeal or dolomite as a source of calcium, they can contain dangerous levels of lead.
What side effects may I notice from receiving Calcium; Vitamin D?
Serious side effects from calcium; vitamin D are uncommon but can occur with large doses, long-term use, or in patients with kidney disease.
Side effects that you should report to your prescriber or health care professional as soon as possible:
• bone or muscle pain
• confusion
• constipation
• depression
• diarrhea
• drowsiness
• dry mouth
• headache
• high blood pressure
• increased thirst
• increased need to pass urine (especially at night)
• irregular heartbeat
• loss of appetite
• lower back pain or pain and difficulty passing urine
• metallic taste
• nausea, vomiting
• seizures
• stomach pain
• unusual tiredness or weakness
• weight loss
Side effects that usually do not require medical attention (report to your prescriber or health care professional if they continue or are bothersome):
• stomach upset
Where can I keep my medicine?
Keep out of the reach of children in a container that small children cannot open.
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:
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.
Although lime (calcium oxide) has been known since ancient times, elemental calcium was first isolated by Sir Humphry Davy in 1808. Today, calcium metal is usually prepared by electrolysis of fused calcium chloride to which a little calcium fluoride has been added. It is used in alloys with other metals, such as aluminum, lead, or copper; in preparation of other metals, such as thorium and uranium, by reduction; and (like barium) in the manufacture of vacuum tubes to remove residual gases.
The metal is of little commercial importance compared to its compounds, which are widely and diversely used. The element is a constituent of lime (see calcium oxide), chloride of lime (bleaching powder), mortar, plaster, cement (see cement, concrete, whiting, putty, precipitated chalk, gypsum, and plaster of Paris. Tremolite, a form of asbestos, is a naturally occurring compound of calcium, magnesium, silicon, and oxygen. Calcium carbide reacts with water to form acetylene gas; it is also used to prepare calcium cyanamide, which is used as a fertilizer. The phosphate is a major constituent of bone ash. The arsenate and the cyanide are used as insecticides. Calcium bicarbonate causes temporary hardness in water; calcium sulfate causes permanent hardness. Generally, calcium compounds show an orange or yellow-red color when held in the Bunsen burner flame.
Although calcium is the fifth most abundant element in the earth's crust, of which it constitutes about 3.6%, it is not found uncombined. It is found widely distributed in its compounds, e.g., Iceland spar, marble, limestone, feldspar, apatite, calcite, dolomite, fluorite, garnet, and labradorite. It is a constituent of most plant and animal matter.
Calcium is essential to the formation and maintenance of strong bones and teeth. In the human adult the bone calcium is chiefly in the form of the phosphate and carbonate salts. A sufficient store of vitamin D in the body is necessary for the proper utilization of calcium. Calcium also functions in the regulation of the heartbeat and in the conversion of prothrombin to thrombin, a necessary step in the clotting of blood.
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.
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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.
