How do I know which calcium supplements provide the most calcium? There are so many different kinds — carbonate, citrate, lactate, gluconate.

Answers from Katherine Zeratsky, R.D., L.D.

The key factor to consider when buying calcium supplements is the amount of elemental calcium the supplements contain. The term "elemental calcium" refers to the amount of calcium in a supplement that's available for your body to absorb. Don't be deceived by the total weight of each tablet, which is simply the weight of the calcium plus whatever it's bound to — such as carbonate, citrate, lactate or gluconate.

If the amount of elemental calcium isn't clearly listed on the label, check the Nutrition Facts label. The amount of elemental calcium will be listed in milligrams (mg) according to "serving size" — generally one or two tablets. The Nutrition Facts label also lists the Percent Daily Value (% Daily Value), which indicates how much one serving provides toward the average daily recommended amount of a given nutrient for most people. For calcium, the % Daily Value is 1,000 mg of elemental calcium. Remember, however, your needs for calcium may vary according to recommendations from your doctor or dietitian.

When choosing calcium supplements, it's also helpful to note how much calcium is in the serving size listed on the label. This will help you determine the number of tablets you must take to meet your individual needs for calcium. Also look for "USP" or "CL" on the label. Supplements that bear The United States Pharmacopeia (USP) or ConsumerLab (CL) abbreviations meet voluntary industry standards for quality, purity, and tablet disintegration or dissolution.

Nov. 15, 2008 See more Expert Answers