Getting the Right Amount of Calcium

JULY 10, 2011
Yvette C. Terrie, BSPharm, RPh

Pharmacists can explain the different forms of calcium available and help patients choose the right supplement to meet their needs. 

Calcium is the most abundant mineral found in the human body. An estimated 99% of the body’s calcium is stored in the bones and teeth, whereas the other 1% is found in the extracellular fluid, intracellular structures, and cell membranes. 1,2 In addition to playing a significant role in the activation of many enzymes and the synthesis of acetylcholine, calcium is responsible for increasing cell membrane permeability, facilitating the absorption of vitamin B12 , and regulating muscle contractions and relaxation. It has a role in plasma clotting factors such as blood coagulation and nerve conduction, and is necessary for the functional integrity of many cells, especially those of the neuromuscular and cardiovascular systems. 1-3 The absorption of calcium is controlled by the small intestine.

Treating Calcium Deficiency

Although calcium is best obtained through dietary sources, many individuals do not obtain sufficient calcium through diet alone. According to recommendations from the National Osteoporosis Foundation (Table 1):

• Adults 50 years and older need a total of 1200 mg of calcium from all sources and 800 to 1000 IUs of vitamin D every day. 4

• Adults younger than age 50 need a total of 1000 mg of calcium from all sources and 400 to 800 IUs of vitamin D every day. 4


Table 1. Recommended Dietary Allowances (RDAs) for Calcium






0-6 months*

200 mg

200 mg


7-12 months*

260 mg

260 mg


1-3 years

700 mg

700 mg


4-8 years

1000 mg

1000 mg


9-13 years

1300 mg

1300 mg


14-18 years

1300 mg

1300 mg

1300 mg

19-50 years

1000 mg

1000 mg

1000 mg

51-70 years

1000 mg

1200 mg


71 years

1200 mg

1200 mg


*Adequate intake

Adapted from reference 1.

The average daily intake of dietary calcium among Americans, however, is only 800 mg; therefore, a vast majority of individuals rely on the use of calcium supplements. 5 The FDA has approved calcium supplements for the treatment and prevention of calcium deficiency, 2 which may result in an increased risk of rickets, osteomalacia, or osteoporosis. 2 Calcium supplements are also approved for treating acid indigestion and the hyperphosphatemia associated with end-stage renal disease. 2

Studies have shown that the use of calcium supplements may also be helpful in alleviating or possibly preventing premenstrual syndrome (PMS). In fact, the American College of Obstetricians and Gynecologists recommends the routine use of calcium supplements in women who experience PMS. 2 Some clinical studies have proposed that calcium may aid in reducing the risk of cardiovascular disease by decreasing intestinal absorption of lipids, increasing lipid excretion, lowering cholesterol levels in the blood, and promoting calcium influx into cells. 1 Several clinical trials have demonstrated a relationship between increased calcium intake and a lower risk of hypertension, and some studies have linked higher calcium intake to weight loss over time.

Counseling Points

There are a variety of calcium supplements on the market (Table 2). Calcium carbonate and calcium citrate are the 2 most common forms of calcium found in supplements. Other forms of calcium include calcium lactate, calcium gluconate, and calcium phosphate. 2 Calcium carbonate supplements contain 40% elemental calcium, and calcium citrate contains 21% elemental calcium. 2 Because calcium carbonate products are insoluble salts, patients should be told to take these supplements with food to augment absorption. 2 Calcium citrate products, on the other hand, can be taken without regard to food. Patients also taking histamine 2 antagonists or proton pump inhibitors may need to take a soluble salt (calcium citrate, calcium lactate, or calcium gluconate. 2

Long-term use of certain pharmacologic agents (eg, systemic corticosteroids, heparin, phenytoin, levothyroxine, methotrexate, cyclosporine, warfarin, gonadotropin-releasing hormone) 2 may inhibit or decrease calcium absorption and may decrease drug absorption. 2 Patients taking these drugs should discuss the use of calcium supplements with their primary health care provider to determine whether they are appropriate. 2 Patients taking calcium supplements should be advised to separate dosing by at least 2 hours when taking iron, zinc, magnesium, and antacids containing aluminum, and by at least 4 hours when taking levothyroxine. 2 In addition, when taking tetracyclines or fluoroquinolones, patients should take calcium supplements 2 hours before or 6 hours after taking the antibiotic. 2

Table 2. Examples of Nonprescription Calcium Supplements

Brand Name

Amount of Elemental Calcium/Active Ingredients

Caltrate 600 D High Potency Tablets

Elemental calcium 600 mg as calcium carbonate, vitamin D 200 IU

Citracal D Caplets

Elemental calcium 315 mg as calcium citrate, vitamin D 200 IU

Os-Cal 500 D Tablets

Elemental calcium 500 mg as calcium carbonate, vitamin D 125 IU

Tums Ultra

Elemental calcium 400 mg as calcium carbonate

Viactiv Soft Chews

Elemental calcium 500 mg as calcium carbonate, vitamin D 100 IU

VitaFusion Calcium 500 mg

Tricalcium phosphate 500 mg, vitamin D3 1000 IU

Nature’s Bounty Calcium 600 D

Elemental calcium 600 mg as calcium carbonate, vitamin D 250 IU

Nature Made Calcium

Calcium Carbonate 500 mg, vitamin D3 200 IU

Calcet Dual Calcium Vitamin D3 

Calcium carbonate 600 mg, vitamin D 750 IU

When assisting patients in the selection of calcium supplements, pharmacists can identify patients at a greater risk for bone loss or osteoporosis due to the use of certain medications or medical conditions. Pharmacists are also in a crucial position to recognize possible contraindications or drug interactions that can occur when certain drugs are used in conjunction with calcium supplements, and make clinical recommendations accordingly.

Because calcium can interfere with the absorption of bisphosphonates, it is important for pharmacists to remind patients to wait at least 30 minutes before taking calcium supplements if they are also taking bisphosphonates such as alendronate, alendronate/cholecalciferol, or risedronate, and to wait at least 60 minutes if taking ibandronate. Aluminumcontaining antacids should also be administered in separate dosing intervals (at least 2 hours apart) when used in conjunction with calcium supplements. 2

Total intake, including calcium found in the diet as well as in multivitamin and calcium supplements, should not exceed doses of 2.5 g per day. Higher doses can be harmful and can result in elevated calcium levels in the urine and renal stones. 2 Patients should be advised that hypercalcemia can result in anorexia, nausea, vomiting, constipation, and polyuria, particularly in those taking high-dose vitamin D formulations. 2

When recommending calcium supplements, pharmacists can take the opportunity to educate women about osteoporosis prevention and the importance of obtaining adequate calcium intake through dietary means and through weight-bearing exercises. Pharmacists should also remind patients that calcium absorption is improved by dividing administration into doses of 500 mg 2 to 3 times a day. 2

Because use of calcium supplements may cause increased incidence of constipation, bloating, and flatulence for some individuals, patients should be reminded about the importance of maintaining sufficient hydration, dietary fiber intake, and routine exercise. 2,5 Patients should be encouraged to discuss prevention and treatment of osteoporosis with their primary health care providers. Finally, pharmacists should take every possible opportunity to educate patients about osteoporosis and empower them with the information necessary to prevent or relieve this condition. PT


Ms. Terrie is a clinical pharmacy writer based in Haymarket, Virginia.


1.      Dietary supplement fact sheet calcium. National Institutes of Health Office of National Diet Supplements Web site. Accessed June 2, 2011.

2.      Huckleberry Y, Rollins C. Essential and conditionally essential nutrients. In: Berardi R, Newton G, McDermott JH, et al, eds. Handbook of Nonprescription Drugs. 16th ed. Washington, DC: American Pharmacists Association; 2009:406-407.

3.      Osteoporosis. Medline Plus Web site. Accessed June 2, 2011.

4.      Calcium Supplements. National Osteoporosis Foundation Web site. Accessed June 2, 2011.                  

5.      Calcium. PDR Health Web site. Accessed June 3, 2011.

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