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All About Calcium Supplements

Anne Chiavacci, RD, MS, MA Brigham and Women's Hospital
Previously published on

Calcium is well known for its role in building and maintaining strong bones and teeth. It also functions in blood clotting, nerve conduction and muscle contraction. There is preliminary evidence that calcium supplements may decrease blood pressure, colon cancer risk, and symptoms of PMS.

It is best to try to meet calcium needs with food sources. For those who find it difficult, calcium supplements are helpful, but not all supplements are equal. The following are some of the most common questions nutritionists are asked about calcium supplementation, and our answers.

How much calcium do I need?

How much calcium you need depends on your age and whether you are pregnant or breast feeding.

Group Milligrams Per Day
1 - 3 years 500 mg
4 - 8 years 800 mg
9 - 18 years 1,300 mg
19 - 50 years 1,000 mg
51+ years 1,200 mg
Pregnancy and breast feeding 1,000 - 3,000 mg

Which foods contain calcium?

Calcium can be found in many foods, not only in dairy products.

Dairy Foods
Yogurt (1 cup) 350 mg
Milk (1 cup) 300 mg
Cheddar cheese (1 oz.) 204 mg
Ricotta cheese, part skim (1/4 cup) 169 mg
Cottage cheese (1 cup) 150 mg
Nondairy Foods
Whole Grain Total cereal (3/4 cup) 1000 mg
Pink salmon with bones, sardines (3 oz., cooked) 181 mg
Black beans (1 cup) 103 mg
Broccoli (1 cup, cooked) 150 mg
Almonds (1 tbsp.) 50 mg
Soy Products
Soy yogurt with calcium (3/4 cup) 300 mg
Soy milk enriched with calcium (1 cup) 300 mg
Tofu, firm or extra firm (1/4 cup) 250 mg
Soy nuts, roasted/salted (1/2 cup) 103 mg

How do I choose a calcium supplement?

Calcium carbonate and calcium citrate are the optimal forms of supplement.

  • Calcium carbonate supplements
    • Viactiv Soft Calcium Chews with vitamins D & K
    • Tums 500
    • Caltrate 600
    • GNC Calcium Complete (400 mg)
    • Os-Cal 500
  • Calcium citrate supplements
    • Citracal
    • Citracal with vitamin D (315 mg)
    • TwinLab Calcium Citrate Caps (300 mg)
    • Some calcium-fortified orange juice (but not all)
    • GNC Calcimate Plus 800 (calcium citrate malate)
    • Solgar Calcium Citrate (250 mg)
    • Citracal Ultradense Calcium Citrate Tablets (200 mg)

Calcium carbonate should be taken with meals because it requires stomach acid to dissolve and absorb. Calcium carbonate has the most calcium per pill (40 percent), therefore fewer pills are needed. Some find calcium carbonate constipating.

Calcium citrate is well absorbed on an empty stomach and does not constipate. The downside is that it has less calcium per pill (20 percent). On the positive side, calcium citrate is less dependent on stomach acid for absorption. Older people often have decreased stomach acid, so the citrate form may be a better choice than calcium carbonate.

Avoid supplements made of dolomite, oyster shell and bone meal which may contain metals and lead. Calcium phosphate, calcium lactate and calcium gluconate are not recommended because they have very small amounts of calcium.

Don't be fooled by ads for coral calcium promoting it as a cure for around 200 diseases including heart disease, cancer and diabetes. Coral calcium is merely calcium carbonate. In June 2003, the U.S. Federal Trade Commission charged marketers with making false claims about the product's health benefits.

What is the difference between total calcium and elemental calcium?

The amount of elemental calcium is the number to use. During digestion, the elemental calcium is released from the compound (carbonate, citrate) and becomes available for absorption. Calcium carbonate provides 40 percent elemental calcium; the other 60 percent is the carbonate ingredient. Therefore, 600 milligrams (mg) of calcium carbonate provides 240 mg elemental calcium. Calcium citrate is 20 percent elemental calcium; 600 mg of calcium citrate provides 120 mg elemental calcium. The number that is part of the brandname (such as Caltrate 600, Os-Cal 500 and TUMS 500 Extra Strength) usually indicates the amount of elemental calcium in each tablet or pill. But you should read the label to be certain.

A USP (United States Pharmacopeia) symbol on the label means that the calcium supplement is free of lead and other metals. It also meets standards for quantity of elemental calcium in the tablet and how well it dissolves. The application for this symbol is voluntary, so a product may be acceptable even if it does not display this symbol. Test your supplement by putting it in a glass of clear vinegar. Stir occasionally. If it dissolves within 30 minutes, it should do so in your stomach too!

What increases or decreases calcium absorption?

Spread out your calcium from foods and supplements throughout the day. For best absorption, take no more than 500 mg calcium at one time. (To avoid calcium toxicity, do not exceed 2,500 mg of elemental calcium per day.)

Vitamin D enhances calcium absorption, so make sure to get 400 to 800 international units (IU) of vitamin D per day.

Oxalic acid found in dark leafy greens, rhubarb, soy and cocoa decreases the absorption of calcium in these foods. Foods high in insoluble fiber (such as whole grains and wheat bran) also can decrease the absorption of calcium taken at the same time.

Phosphoric acid in dark sodas can interfere with your body's absorption of calcium. Prolonged use of magnesium-containing laxatives compromises calcium absorption as well.

Here are some other factors to consider:

  • Caffeine increases calcium lost in the urine. Limit yourself to one to two cups of caffeinated coffee or soda per day.
  • Excess sodium in the diet also increases calcium excretion. Every 500 mg of sodium over 2,400 mg per day causes the body to excrete 10 mg of calcium.
  • Taking calcium supplements with iron or zinc compromises the absorption of these minerals.
  • Calcium decreases the absorption of certain drugs (bisphosphonates, thyroid, some antibiotics). Other drugs can increase calcium needs (corticosteroids, some diuretics).

The Bottom Line

Calcium is needed for healthy bones, teeth nails and muscle tissue. It also assists in blood clotting and heart and nerve functions. Calcium can be obtained through diet (food sources) or through supplements. It is important to review your medications with your doctor, pharmacist, or nutritionist before starting a calcium supplement.


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