Over-the-Counter Calcium Supplements

How to choose a calcium supplement

In general, we recommend using a calcium supplement for individuals who do not meet their daily requirements through diet alone. Choose a national brand that meets U.S.P (United States Pharmacopeia) standards so that you can be sure that the chosen supplement dissolves and is absorbed easily, as well as to guarantee the purity of the supplement. Avoid “natural” sources such as bone meal or dolomite as they may contain toxic ingredients such as lead or mercury.

There are a multitude of calcium supplements that are available. The following are just a sampling of effective calcium formulations on the market to help you choose wisely.

Calcium carbonate
Calcium carbonate provides 40% elemental calcium. This means that a product which is 1,250 milligrams (mg) of calcium carbonate yields 500 mg of elemental calcium. Advantages of calcium carbonate are that it is probably the most cost-effective supplement; it has the highest percentage of elemental calcium and it has a track record of effectiveness. Calcium carbonate is best taken with meals to be properly absorbed. A disadvantage can be that for some individuals calcium carbonate may cause constipation or gas. Should these symptoms arise, try to drink plenty of fluids, get enough exercise, and add adequate amounts of fiber in your diet. If these measures are unsuccessful, then switching to another calcium formulation is recommended. The following are some national brands of calcium carbonate formulations. Note that Tums and Rolaids can be used safely as an antacid or calcium supplement. They do not contain other medication—only calcium carbonate. If you consider other antacid brands, read the labels carefully to avoid aluminum containing brands.
Name Type Strength per tab
In (mgs)
Elemental Calcium
(in mgs)
Alka-Mints calcium carbonate 850 340
Caltrate calcium carbonate 1500 600
OsCal calcium carbonate 625 or 1250 250 or 500
Rolaids calcium carbonate 550 220
Titralac Tablets calcium carbonate 420 168
Titralac Liquid (1tsp) calcium carbonate 1000 400
Tums and Tums E-X calcium carbonate 500 or 750 200 or 300
Tums Ultra and Tums 500 calcium carbonate 1000 or 1250 400 or 500

Calcium citrate
Calcium citrate provides 21% elemental calcium. Studies using calcium citrate show that it is an easily absorbed calcium supplement. It can be taken at any time without regard to food. The disadvantages are that it has a relatively lower percent of elemental calcium than calcium carbonate, therefore, you have to take more tablets of it to equal the same amount of elemental calcium in calcium carbonate. Calcium citrate is also a significantly more expensive supplement.
Citracal Liquidtabs calcium citrate 2376 mg/tab 500
Citracal calcium citrate 950 mg/tab 200
Citracal Caplets + D calcium citrate 1500 315 + 200 I. U.
vitamin D3

Calcium phosphate
Tribasic calcium phosphate provides 39% elemental calcium. It also is an easily dissolved and well-absorbed supplement that should not cause gas or constipation. It can be taken anytime. Calcium phosphate tends to be relatively more expensive than calcium carbonate, but less expensive than calcium citrate. Calcium phosphate is the formulation used in specially calcium fortified orange juice, soy milk and rice milk available.
Posture calcium phosphate 1500 mg/tab 600 mg
Posture-D calcium phosphate 1500 mg/tab 600 mg + 125 I.U.
vitamin D3

How to take calcium supplements

Calcium is best absorbed if consumed in split doses throughout the day. Generally, our bodies can only absorb about 500 mg of elemental calcium at a time. We recommend that you choose a particular hour, or meal, to take the supplement regularly, thereby establishing a habit. Some calcium experts recommend taking a dose of calcium just before bedtime.

Certain substances in foods such as spinach, rhubarb, caffeine containing drinks, and whole grains are believed to reduce the amount of calcium your body can absorb. In truth, they will have little impact on the calcium supplement or calcium-containing foods eaten at the same time. These foods are important and should be included in a healthy, well-balanced diet. It would require eating very large amounts of wheat bran, for example, to have a significantly negative effect on calcium absorption.

Aluminum-containing antacids, iron supplements and some prescription medications will interfere with absorption and retention of your calcium supplement and vice versa. Consult your physician about the possibility of such an interaction.


Adapted from the Calcium Information Center.