How should I choose from so many calcium supplements?

David Slovik, MD
Endocrinology Diabetes & Metabolism
A dizzying array of calcium supplements is available -- so many, in fact, that choosing one can be tricky. You can choose from flavored chews, pills, chewable tablets, and liquids. When making a decision, it's wise to consider cost, convenience, and how well your body tolerates the supplement.
The calcium in supplements is found in combination with another substance, typically carbonate or citrate. (Some products combine calcium with phosphate, lactate, or gluconate, but these are less common and tend to be more expensive.)
Calcium carbonate tends to be the best value, because it has the highest amount of elemental calcium. Elemental calcium is the actual amount of calcium in each supplement. The compound calcium carbonate contains 40% calcium by weight, while calcium citrate is 21% calcium. This means that you may need to take more tablets of a calcium citrate product in order to meet your daily needs.
Because calcium carbonate requires stomach acid for absorption, it's best to take this product with food. Most people tolerate calcium carbonate well. However, some people complain of mild constipation or feeling bloated. Some well-known calcium carbonate products include Caltrate, Viactiv Calcium Chews, Os-Cal, and Tums.
On the other hand, calcium citrate is absorbed more easily than calcium carbonate and can be taken on an empty stomach. But as mentioned above, you may need to take more tablets to get your daily requirement. Calcium citrate is preferred in patients receiving proton pump inhibitors since these medications reduce the acid in the stomach, thus making calcium carbonate harder to absorb. Calcium citrate products include Citracal and GNC Calcimate Plus 800.
In weighing your options, check the labels of products to see what the serving size is and what the "% Daily Value" for calcium is. The "% Daily Value" reflects how much elemental calcium is in the product. The Daily Value is set by Food and Drug Administration (FDA) regulations and is not the same as the Recommended Dietary Allowance (RDA). Currently, the Daily Value for calcium is 1,000 mg -- the RDA for people ages 19 to 50, not the 1,200 mg RDA for older adults. Since the "% Daily Value" for all calcium supplements is 1,000 mg, simply multiply the percentage listed by 10 to find out how much elemental calcium the product contains. For example, if the label says the product contains 40% of the Daily Value, it has 400 mg of elemental calcium.
To choose a good calcium supplement, first look for brand names you recognize. And be sure to check the bottle for the United States Pharmacopeia (USP) label, which indicates that the product meets quality control standards.

Steer clear of products containing oyster shell, bone meal or dolomite, because these ingredients can potentially be contaminated with lead or other toxic metals.

Choose supplements made from calcium citrate or calcium carbonate, and bypass those made from calcium phosphate, calcium lactate or calcium gluconate, because these contain only small amounts of "elemental calcium" (the type of calcium you need). Read the label to see how much calcium the supplement contains.

Look for supplements containing 500 milligrams (mg) of calcium per tablet. Your body absorbs calcium best in that amount or less, although you'll still reap calcium's bone-building benefits if you take your recommended daily dose all at once. Most adults need 1,000 milligrams (mg) of calcium per day.
The best supplement is the one that meets your needs based on tolerance, convenience, cost and availability. Calcium supplements are available with and without a prescription in a wide range of preparations (i.e. tablets, chews, and liquids) and in various strengths. Calcium exists in nature only in combination with other substances called compounds. These compounds contain different amounts of elemental calcium. The elemental calcium is the amount of calcium that your body is actually getting (able to absorb) from the supplement.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.