Calcium is critical to the development and maintenance of bones and teeth. It also plays an important role in controlling the heartbeat, maintaining proper blood pressure, clotting blood, transmitting nerve impulses, contracting and relaxing muscles, maintaining the integrity of mucosal membranes and cell walls, and activating enzymes such as lipase, adenosine triphosphatase (ATPase), succinate dehydrogenase, and choline acetylase.

Calcium comprises approximately 2% of an adult's body weight, more than any other mineral; the amount of calcium in an infant's body is approximately 0.8%. The rate of absorption is greatest in childhood (50% to 70% of the calcium ingested), decreasing in adults to 10% to 40%. As the intake of calcium increases, the percent absorbed decreases. Vitamin D (especially D3, or cholecalciferol) is the most important vitamin for assisting in the absorption of calcium. The antioxidant vitamins A, C, and E are also important. Lactose aids absorption, improving the value of milk as a source of calcium. Magnesium and phosphorus are significant in assisting in proper absorption. Recommended ratios of calcium to each of these minerals range from 1:2 to 2:1, but are currently under review. Iron, zinc, and manganese play a less important role. Stress and lack of exercise can cause negative calcium balances.

Parathyroid hormone (PTH), vitamin D, and the thyroid hormone calcitonin act to maintain normal blood calcium levels of 9 to 11 mg/100 ml. PTH stimulates the release of calcium from bone and decreases excretion from the kidney, and it acts with vitamin D to increase the rate of absorption, if blood levels are reduced. Calcitonin lowers blood calcium levels that are too high by inhibiting calcium release from bone.

Average dietary calcium intakes in Americans are lower than recommended levels; the problem is particularly acute with women. Calcium deficiency has been linked to stunted growth, bone deformities, rickets, osteoporosis, osteomalacia, muscle spasms, leg cramps, high blood pressure, and colon cancer. Recent studies question the role of calcium in decreasing the incidence of colon cancer. Although kidney stones can result from toxic levels of calcium in certain susceptible individuals, high calcium intake can actually decrease the risk of kidney stones, and large calcium supplements are accepted therapy for kidneys stones associated with intestinal hyperoxalosis.

• Rich sources: cheeses (especially Parmesan, Romano, Gruyère, Swiss, provolone, Monterey Jack, Edam, cheddar, Muenster, Gouda, Tilsit, Colby, caraway, brick, Roquefort, Port du Salut, Cheshire, Havarti, fontina, mozzarella, feta), wheat-soy flour, blackstrap molasses, rennin
• Good sources: almonds, Brazil nuts, caviar, dried figs, dark greens (turnip, dandelion, collard, mustard), hazelnuts, ice cream, kale, bok choy, broccoli, cabbage, milk, oysters, sardines, soybean flour, yogurt. (Milk and dairy products account for about 75% of dietary calcium in Americans; butter, cream cheese, and other high-fat dairy products contain little or no calcium.)
• Many herbs, spices, and seaweeds supply calcium (e.g., basil, chervil, cinnamon, dill weed, fennel, fenugreek, ginseng, kava kava, kelp, marjoram, oregano, parsley, poppy seed, sage, savory).

The mineral calcium is the fifth most prevalent element in the biosphere. The calcium ion (Ca²⁺) can form bonds with up to 12 oxygen atoms and is nearly unique in its ability to interact with the peptide chain.

Calcium citrate: soluable (optimizing absorption); most bioavailable; safe levels of lead; easily digested. It is recommended for elderly patients and persons taking acid-lowering medications, and it may be more effective in hypertension control than calcium carbonate. The citrate effects may inhibit kidney stone formation.

Calcium carbonate: Lead levels are safe if it is a refined product. Some antacids (Rolaids/Tums) contain 500 mg of calcium carbonate.

Calcium gluconate and calcium lactate: soluble; safe levels of lead

Calcium chloride: not recommended (irritates the gastrointestinal tract)

Homeopathic calcium medications and their uses:

• Calcarea carbonica: backache, pain
• Calcarea fluorica: tissue elasticity
• Calcarea phosphorica: fatigue, discontentment, discomfort, pain
• Calcarea sulfurica: sores, wounds, abscesses, boils, cysts

• Osteoporosis: to preserve adequate mineral mass, prevent loss of structural bone components, maximize repair of damaged bones, prevent loss of bone mass
• Hypertension: to reduce blood pressure (most effective in elderly, African-Americans, and salt-sensitive hypertension patients, but not in salt-resistant hypertensive patients)
• Premenstrual syndrome (PMS): to relieve menstrual cramps, irritability or apprehension, muscle cramps
• Pregnancy: to reduce pregnancy-induced hypertension and prevent preeclampsia
• Menopause: to reduce headaches, irritability, insomnia, depression
• Dental: to improve loose teeth, gingivitis, periodontal disease
• Cardiovascular: to reduce heart irregularity, lower cholesterol

Recommendations for adequate calcium intakes promulgated by the National Academy of Science Food and Nutrition Board in 1997:

Infants:

• birth to 6 months: 210 mg/day
• 6 months to 1 year: 270 mg/day

Children:

• 1 to 5 years: 500 mg/day
• 6 to 8 years: 800 mg/day

Adolescents:

• 9 to 18 years: 1,300 mg/day

Adults:

• 19 to 50 years: 1,000 mg/day
• Over 50 years: 1,200 mg/day

Lactating or pregnant women:

• 14 to 18 years: 1,300 mg/day
• 19 years and older: 1,000 mg/day

Ideally, supplements should be taken in small doses throughout the day, and six to eight 8-oz. glasses of water should be consumed to avoid constipation.

Nutritional toxicity is an increase in blood calcium levels (hypercalcemia) because intake is too high, or an increase of urine calcium excretion resulting in calcification of the kidneys or development of renal stones. Results of hypercalcemia include decreased gastrointestinal and muscle tone, kidney failure, emotional deterioration, large urine volumes, constipation, nausea, confusion, coma, and ultimately death. Doses of 5,000⁺ mg/day are toxic. Osteopetrosis may result from continuous high calcium intake.

• Unrefined calcium carbonate, especially if derived from limestone or oyster shells, dolomite, and bone meal calcium supplements may contain toxic levels of lead.
• Doses above 2,000 mg/day may increase the risk of kidney stones and soft-tissue calcification.
• Calcium chloride is contraindicated in hypocalcemia caused by renal insufficiency.

Because calcium supplements may interfere with alendronate absorption, they should be taken two hours before or after the drug (PDR 1998).

In a study with eight male subjects, 5 mL of aluminum hydroxide gel (2.4 gm qid) coadministered with calcium citrate (950 mg qid) for three days increased urinary aluminum excretion (Coburn et al. 1991). The finding of enhanced aluminum excretion is consistent with another study involving 30 healthy women who were given calcium citrate (800 mg elemental calcium/day) (Nolan et al. 1994). Urinary and plasma aluminum levels were increased significantly. This effect may have been related to aluminum derived only from dietary sources because the women were not receiving aluminum-based antacids.

Two doses of amiloride (2.5 mg/day) reduced urinary calcium in subjects with kidney stones (Leppla et al. 1983). This decrease in calciuresis was enhanced when amiloride was coadministered with two doses of hydrochlorothiazide (25 mg/day).

Oral administration of 500 mg calcium salts (lactate, gluconate, and carbonate) with atenolol (100 mg) reduced plasma levels of atenolol by 51% in six healthy subjects (Kirch et al. 1981). Long-term coadministration increased the elimination half-life and led to atenolol accumulation. Subsequent studies did not confirm an interaction between atenolol and calcium antacids (Gugler and Allgayer 1990). Until more is known, individuals on beta-blockers should have their blood pressure checked before and after the addition of calcium antacids or supplements to their atenolol regimen.

Hypocalcemia can negate the therapeutic effects of digoxin, while hypercalcemia may predispose a patient to arrhythmias and digoxin toxicity (Hines Burnham et al. 2000). In one study, patients with digoxin-induced cardiotoxicity had serum concentrations of the drug that were within therapeutic range but they had higher calcium to potassium ratios (Sonnenblick et al. 1983). Normal levels of calcium should be maintained during digoxin treatment. Patients taking digoxin should have calcium blood levels monitored closely.

Conjugated estrogens lower calcium excretion (Lobo et al. 1985) and increase calcium absorption in postmenopausal women (Gallagher et al. 1980). The enhanced absorption appears to be due to an increase in serum 1,25(OH)2D. Early postmenopausal women taking calcium supplements with estradiol (or conjugated estrogens) have been shown to have significantly greater gains in bone mineral density than women taking HRT alone (Pines et al. 1999). Calcium supplementation is highly recommended in all postmenopausal women. For women 51 years or older, the Dietary Reference Intake (DRI) for calcium is 1200 mg/day (Institute of Medicine 1997).

In a retrospective study, coronary artery bypass graft patients who received both a bypass prime with a high calcium concentration and gentamicin perioperatively had a higher incidence of renal failure compared with those who received only the prime, gentamicin alone, or neither (Schneider et al. 1996). Concomitant administration of calcium may potentiate gentamicin-induced nephrotoxicity.

Quinolone antibiotics form chelates with metal cations, such as aluminum, magnesium, calcium, iron, zinc, copper, and manganese (Kara et al. 1991; Li et al. 1999), which significantly reduces the absorption of these medications (Balfour and Wiseman 1999; Brouwers 1992; Campbell and Hasinoff 1991). Dietary supplements and antacids containing aluminum and magnesium should be taken two to four hours before or after administration of these antibiotics (Hines Burnham et al. 2000; Li et al. 1999).

Tetracyclines form chelates with divalent and trivalent cations, including iron, aluminum, magnesium, and calcium (Neuvonen 1976). These chelates are poorly soluble and can significantly reduce the absorption and efficacy of tetracyclines (Hines Burnham et al. 2000; Neuvonen 1976). Calcium salts should be administered at least two hours before or after tetracyclines (Hines Burnham et al. 2000).

Thiazide diuretics may cause hypercalcemia by decreasing calcium excretion (Hines Burnham et al. 2000). Treatment with a combination of hydrochlorothiazide (50 mg/day) and vitamin D in six postmenopausal women with osteoporosis for six months reduced urinary calcium excretion by 22% (Sakhaee et al. 1984). In this study, it was noted that the combination of hydrochlorothiazide and vitamin D also decreased calcium absorption by 25%.

However, the ability of thiazide diuretics to decrease urinary calcium excretion has been associated with less risk of hip fractures in patients taking these medications (Rejnmark et al. 1998).

It has been reported that calcium salts may reverse the clinical effects and toxicities associated with verapamil (Hines Burnham et al. 2000). However, pretreatment with intravenous calcium in patients with supraventricular arrhythmias reduced the incidence of hypotensive side effects without compromising the antiarrhythmic effect of verapamil (Haft and Habbab 1986; Weiss et al. 1983). Calcium also influenced blood pressure by restoring it to control values when administered after treatment with verapamil (Weiss et al. 1983).

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