Calcium Supplements

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Calcium supplements


Calcium supplements are elemental forms of calcium, an essential mineral for human health that may be taken to supplement calcium obtained from dietary sources or to address a calcium deficiency. Most supplements contain one of two forms of calcium—calcium carbonate and calcium citrate. Since vitamin D is needed to help the body absorb calcium, many calcium supplements also contain vitamin D.


Calcium is the most abundant mineral in the body. Between one and two percent of body weight is calcium—the average male has about three pounds of calcium; the average female contains about two pounds—and nearly all of it—99%—is concentrated in the bones and teeth. The remaining one percent is in the cells of the body, blood, and extracellular fluid (the fluid between cells).

Calcium is vitally important for building and maintaining strong teeth and bones. It also is necessary for regulating the heart's rhythm, controlling blood pressure , initiating blood clotting, wound healing, the transmission of impulses between nerve cells, the production and secretion of enzymes and hormones that regulate fat metabolism, and muscle contraction. Calcium helps to maintain connective tissue throughout the body, and it may help to prevent gum disease and some cancers, such as colon cancer . It also is involved in many cellular processes such as gene regulation.

The body requires calcium every day and a constant level of this essential mineral is maintained to enable calcium-dependent body functions. The normal level of blood calcium is 9 to 11.5 mg/100 ml. The continuous need for calcium is fulfilled either by dietary calcium, the amount of absorbable calcium ingested daily in the form of food, or by dietary supplements . Dietary sources of calcium include dairy products, leafy green vegetables, sardines, salmon, tofu, and rhubarb. When dietary sources are insufficient to meet the body's calcium demands, then it is drawn from bone, where calcium is stored.

Bone is living tissue; it is continuously forming, breaking down, and reforming. Calcium is deposited into forming bone and released during the breakdown of bone. The equilibrium between bone formation and bone loss changes throughout life with the most formation and least amount of breakdown during childhood when most growth occurs. Parathyroid hormone, which causes transfer of calcium from bone into the bloodstream, and calcitriol, the active form of vitamin D, help to maintain calcium balance by preventing either calcium deficit or excess.

Among older adults, especially women who are past menopause , bone breakdown predominates, resulting in bone loss, which in turn increases the risk of developing osteoporosis . Osteoporosis is the condition in which bones become thinner, weaker, and less dense, in part because they lack calcium. Osteoporosis increases the risk of fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones and can lead to changes in posture.

Calcium deficiency

Calcium deficiency, also called hypocalcemia, may result from medical problems that cause decreased calcium absorption or increased calcium loss through excretion. Less commonly, calcium deficiency may be caused by chronically inadequate calcium intake or low vitamin D intake. Conditions such as kidney failure, surgical removal of the stomach, and the use of diuretics , drugs commonly used to treat high blood pressure, can lead to calcium deficiency.

Although low levels of calcium may not produce any symptoms at all, when they do, the symptoms may include:

  • numbness and tingling in fingers
  • muscle cramps
  • convulsions
  • fatigue
  • poor appetite
  • mental confusion
  • abnormal heart rhythms

When there is not enough calcium in the diet or a sudden loss of calcium from the body, calcium is drawn from the bones to maintain adequate levels of calcium in the blood. Preventing calcium depletion from the bones is one important measure that can be taken to prevent osteoporosis.

Recommended dosage

The body's ability to absorb calcium decreases with advancing age, which is why the recommended intake for adults older than age 51 is higher than it is for younger adults. For adults ages 19 to 50, the recommended adequate intake for calcium is 1,000 mg/day. For adults age 51 and older, the recommended adequate intake for calcium is 1,200 mg/day, almost as much as the recommended intake of 1,300 mg/day for older children (ages 9 to 13) and teenagers (ages 14 to 18).

The two main forms of calcium found in supplements are carbonate and citrate. Calcium carbonate is the most common because it is inexpensive and convenient. The absorption of calcium citrate is similar to calcium carbonate, but individuals have to take more pills of calcium citrate to get the same amount of calcium. One advantage of calcium citrate over calcium carbonate is better absorption in those individuals who have decreased stomach acid.

Calcium absorption also depends on the total amount of calcium consumed at one time and whether the calcium is taken with food or on an empty stomach. Absorption from supplements is best in doses 500 mgor less because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases. Therefore, someone taking 1,000 mg of calcium in a supplement should take 500 mg twice a day instead of 1,000 mg calcium at one time.


Although low intake of calcium can lead to calcium deficiency and related health problems, excessively high calcium intake also may have harmful effects on health. High calcium levels in the blood, called hypercalcemia, can impair kidney function and decrease the absorption of other minerals, including iron, zinc , magnesium, and phosphorus.

Dangerously high calcium levels and calcium toxicity rarely occur; however, if an excessive amount of calcium—more than 2,500 mg of calcium per day—is consumed in the form of dietary supplements, then the excess calcium can lead to the formation of kidney stones . Although excessively high calcium levels can result from ingestion of very large amounts and high doses of vitamin D and calcium supplements, it is rarely attributable to consuming too much calcium from food. More often, elevated levels of calcium are associated with a disease process such as advanced stages of cancer .


  • Which type of calcium supplement is more readily absorbed?
  • When, and how often, should calcium supplements be taken?
  • What side effects might be caused by taking calcium supplements?
  • What are the benefits and risks of taking calcium supplements?
  • Which over-the-counter and prescription drugs may interact with calcium supplements?

Several studies suggest that calcium supplementation may help to protect against cardiovascular disease and favorably effect blood pressure and the ratio of high-density lipoprotein (HDL is the so-called good cholesterol associated with heart health) and low-density lipoprotein (LDL is the so-called bad cholesterol associated with heart disease ) cholesterol in healthy postmenopausal women. However, in 2008 some research suggested that calcium supplementation may increase the risk for heart attacks, strokes, and other cardiovascular diseases in older women, possibly by speeding up deposit of calcium in the walls of blood vessels.

Similarly, because high levels of calcium may be linked to the development of prostate cancer , calcium supplements may not be advisable for men unless they are recommended by a physician or other health professional to address a specific health or nutritional problem.

Persons with kidney disease, parathyroid disease, sarcoidosis , or gastrointestinal disorders should consult with their physicians before taking calcium supplements.

Side effects

The most common side effect associated with use of calcium supplements is stomach upset and gas. Calcium citrate is more readily absorbed and less likely to produce constipation and gas than calcium carbonate. It also is less likely to increase the risk of developing kidney stones.

Most people do not experience serious side effects from calcium supplements; however, their use may produce one or more of the following side effects:

  • painful muscles or bones
  • constipation or diarrhea
  • depression or confusion
  • drowsiness or weakness
  • headache
  • increased thirst and increased urination
  • dry mouth or metallic taste
  • nausea, vomiting, stomach pain
  • loss of appetite
  • seizures


Calcium supplements are known to interact with many prescription and over-the-counter drugs. Some medications may not be as effective when taken with calcium supplements, and others may interact with calcium to either elevate or deplete calcium in the body. For example, when calcium and vitamin D are taken with diuretics, there is increased risk of developing hypercalcemia—elevated levels of calcium in the blood and urine. Similarly, calcium supplements, vitamin D, and digoxin, a drug used to treat people with heart problems, can cause elevated blood levels of calcium.

Calcium absorption may be reduced if a supplement is taken with high-fiber foods or beverages containing caffeine or alcohol. Generally, calcium supplements should be taken separately, or at least two hours before or after consuming other medications. Calcium carbonate, which is found in antacids , should, however, be taken with food to improve its absorption.

Examples of prescription and over-the-counter drugs that interact with calcium are:

  • aspirin and other salicylates
  • antacids that contain aluminum or magnesium
  • anticoagulants
  • chlorpromazines
  • estrogens
  • etidronate
  • fluoroquinolones, a class of antibiotics that includes ciprofloxacin
  • glucocorticoids, such as prednisone
  • iron supplements
  • levothyroxine, a synthetic thyroid hormone
  • meperidine
  • mexiletine
  • mineral oil or stimulant laxatives
  • nalidixic acid
  • nicardipine
  • nimodipine
  • oxyphenbutazone
  • para-aminosalicyclic acid (PAS)
  • penicillin, tetracycline, and similar antibiotics
  • pentobarbital
  • phenylbutazone
  • phenytoin, an anti-convulsant
  • pseudoephedrine
  • quinidine
  • tiludronate disodium, a drug used to treat Paget's disease


Hypercalcemia —abnormally high blood calcium level

Hypocalcemia —abnormally low blood calcium level

Osteoporosis —A decrease in bone density that occurs when bones lose calcium and other essential elements. Decreasing bone mass increases the risk of fractures.



Rakel, David. Rakel: Integrative Medicine, 2nd ed. Philadelphia: Saunders, 2007.

Schulman, Robert, and Carolyn Dean. Solve It with Supplements: The Best Herbal and Nutritional Supplements to Help Prevent and Heal More than 100 Common Health Problems. New York: Rodale, 2007.


“Dietary Supplement Fact Sheet: Calcium.” Office of Dietary Supplements, National Institute of Health. September 23, 2005 [cited March 16, 2008].

Park, S. Y., S. P. Murphy, L. R. Wilkens, et al.. “Calcium, Vitamin D, and Dairy Product Intake and Prostate Cancer Risk: The Multiethnic Cohort Study.” American Journal of Epidemiology 166, no. 11 (December 1, 2007).


NIH Osteoporosis and Related Bone Diseases, National Resource Center, 2 AMS Circle, Bethesda, MD, 20892-3676, (202) 223–0344, (800) 624–BONE, (202) 466-4315, [email protected],

Barbara Wexler MPH