Calcium is essential for many functions in the body, including:

  • regulating the heartbeat
  • conducting nerve impulses
  • stimulating hormone secretions
  • clotting blood
  • building and maintaining healthy bones.

Calcium is a mineral found in many foods. Getting enough of this nutrient is important because the human body cannot make it. Even after you are fully grown, adequate calcium intake is important because the body loses calcium every day through the skin, nails, hair, and sweat, as well as through urine and feces. This lost calcium must be replaced daily through the diet. Otherwise, the body takes calcium from the bones to perform other functions, which makes the bones weaker and more likely to break over time.

Experts recommend that adults get 1,000 to 1,200 mg (milligrams) of calcium each day. Although food is the best source of calcium, most Americans do not get enough of it from food sources. Calcium-fortified foods (such as orange juice, bread, cereals, and many others on grocery shelves) and calcium supplements can fill the gap by ensuring that you meet your daily calcium requirement.

What to Look for in a Calcium Supplement

Calcium exists in nature only in combination with other substances. These substances are called compounds. Several different calcium compounds are used in supplements, including:

  • calcium carbonate
  • calcium phosphate
  • calcium citrate.

These compounds contain different amounts of elemental calcium, which is the actual amount of calcium in the supplement. Read the label carefully to determine how much elemental calcium is in the supplement and how many doses or pills to take.

Calcium supplements are available without a prescription in a wide range of preparations and strengths, which can make selecting one a confusing experience. Many people ask which calcium supplement they should take. The "best" supplement is the one that meets your needs. Ask yourself these questions:

  • How well does my body tolerate this kind of supplement? Does it cause any side effects (such as gas or constipation)? If so, you may want to try a different type or brand.
  • Is this kind of supplement convenient? Can I remember to take it as often as recommended each day?
  • Is the cost of this supplement within my budget?
  • Is it widely available? Can I buy it at a store near me?

Other Important Things to Consider

Purity. Choose calcium supplements with familiar brand names. Look for labels that state "purified" or have the USP (United States Pharmacopeia) symbol. Avoid supplements made from unrefined oyster shell, bone meal, or dolomite that don't have the USP symbol because they may contain high levels of lead or other toxic metals.

Absorbability. The body easily absorbs most brand-name calcium products. If you aren't sure about your product, you can find out how well it dissolves by placing it in a small amount of warm water for 30 minutes and stirring it occasionally. If it hasn't dissolved within this time, it probably will not dissolve in your stomach. Chewable and liquid calcium supplements dissolve well because they are broken down before they enter the stomach.

The body best absorbs calcium, whether from food or supplements, when it's taken several times a day in amounts of not more than 500 mg, but taking it all at once is better than not taking it at all. Calcium carbonate is absorbed best when taken with food. Calcium citrate can be taken anytime.

Tolerance. Some calcium supplements may cause side effects, such as gas or constipation, for some people. If simple measures (such as increasing your intake of fluids and high-fiber foods) do not solve the problem, you should try another form of calcium. Also, it is important to increase the dose of your supplement gradually: take just 500 mg a day for a week, and then slowly add more calcium. Do not take more than the recommended amount of calcium without your doctor's approval.

Calcium interactions. It's important to talk with a doctor or pharmacist about possible interactions between calcium supplements and your over-the-counter and prescription medications. For example, calcium supplements may reduce the absorption of the antibiotic tetracycline. Calcium also interferes with iron absorption. So you should not take a calcium supplement at the same time as an iron supplement -- unless the calcium supplement is calcium citrate or the iron supplement is taken with vitamin C. Any medications that need to be taken on an empty stomach should not be taken with calcium supplements.

Combination Products

Calcium supplements are available in a bewildering array of combinations with vitamins and other minerals. Calcium supplements often come in combination with vitamin D, which is necessary for the absorption of calcium. However, calcium and vitamin D do not need to be taken together or in the same preparation to be absorbed by the body. Minerals such as magnesium and phosphorus also are important but usually are obtained through food or multivitamins. Most experts recommend that nutrients come from a balanced diet, with multivitamins used to supplement dietary deficiencies.

Getting enough calcium -- whether through your diet or with the help of supplements -- will help to protect the health of your bones. However, this is only one of the steps you need to take for bone health. Exercise, a healthy lifestyle, and, for some people, medication are also important.

For Your Information

This publication contains information about medications used to treat the health condition discussed here. When this fact sheet was printed, we included the most up-to-date (accurate) information available. Occasionally, new information on medication is released.

For updates and for any questions about any medications you are taking, please contact the U.S. Food and Drug Administration at:

U.S. Food and Drug Administration

Toll Free: 888-INFO-FDA (888-463-6332)

For updates and questions about any statistics, please contact the Centers for Disease Control and Prevention's National Center for Health Statistics toll free at 800-232-4636 or visit its Web site at

NIH Osteoporosis and Related Bone Diseases ~ National Resource Center

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Phone: 202-223-0344
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The NIH Osteoporosis and Related Bone Diseases ~ National Resource Center provides patients, health professionals, and the public with an important link to resources and information on metabolic bone diseases. The mission of NIH ORBD~NRC is to expand awareness and enhance knowledge and understanding of the prevention, early detection, and treatment of these diseases as well as strategies for coping with them.

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