Calcium is the most abundant mineral in the body, making up nearly 2% of total body weight. More than 99% of the calcium in your body is found in your bones, but the other 1% is perhaps just as important for good health. Many enzymes depend on calcium in order to work properly, as do your nerves, heart, and blood-clotting mechanisms.

To build bone, you need to have enough calcium in your diet. But in spite of calcium-fortified orange juice and the best efforts of the dairy industry, most Americans are calcium deficient.1 Calcium supplements are a simple way to make sure you are getting enough of this important mineral.

One of the most important uses of calcium is to help prevent and treat osteoporosis, the progressive loss of bone mass to which menopausal women are especially vulnerable. Calcium works best when combined with vitamin D.

Other meaningful evidence suggests that calcium may have an additional important use: reducing PMS symptoms.

Requirements

Here are the recommendations from the Institute of Medicine:198

  • 0-6 months: 200 mg
  • 7-12 months: 260 mg
  • 1-3 years: 700 mg
  • 4-8 years: 1,000 mg
  • 9-18 years: 1,300 mg
  • 19-50 years: 1,000 mg
  • 51-70 years
    • Males: 1,000 mg
    • Females: 1,200 mg
  • 71 and older: 1,200 mg

The recommendations for women who are pregnant or nursing are:

  • Under 19 years: 1,300 mg
  • 19 years and older: 1,000 mg

Food Sources

The National Institutes of Health's Office of Dietary Supplements offers this list of foods that are high in calcium:201

Food Serving size Calcium content
(milligrams [mg])
% Daily Value
Yogurt, plain, low-fat 8 ounces 415 42
Orange juice, calcium-fortified 6 ounces 375 38
Yogurt, fruit, low-fat 8 ounces 338-384 34-38
Mozzarella, part-skim 1.5 ounces 333 33
Sardines, canned in oil, with bones 3 ounces 325 33
Cheddar cheese 1.5 ounces 307 31
Milk, non-fat 8 ounces 299 30
Milk, reduced-fat 8 ounces 293 29
Milk, buttermilk 8 ounces 282-350 28-35
Milk, whole 8 ounces 276 28
Tofu, firm (with calcium sulfate) ½ cup 253 25
Pink salmon with bones, canned 3 ounces 181 18
Cottage cheese, 1% milk fat 1 cup 138 14
Tofu, soft (with calcium sulfate) ½ cup 138 14
Instant breakfast drink 8 ounces 105-250 10-25
Frozen yogurt, vanilla ½ cup 103 10
Ready-to-eat cereal, calcium-fortified 1 cup 100-1,000 10-100
Turnip greens, fresh, boiled ½ cup 99 10
Kale, fresh, cooked 1 cup 94 9
Kale, raw, chopped 1 cup 90 9

In addition to food sources, many forms of calcium supplements are available on the market, each with its own advantages and disadvantages.

Calcium Absorption

To absorb calcium, your body also needs an adequate level of vitamin D (for more information, see the article on Vitamin D).

Various medications may impair calcium absorption or metabolism, either directly or through effects on vitamin D. People who use these may benefit by taking extra calcium and vitamin D. Implicated medications include corticosteroids,30-32heparin,33-35isoniazid,36-38 and anticonvulsants.39-45Note:Calcium carbonate might interfere with the effects of anticonvulsant drugs, and for that reason should not be taken at the same time of day.46,47

Naturally Derived Forms of Calcium

These forms of calcium come from bone, shells, or the earth: bonemeal, oyster shell, and dolomite. Animals concentrate calcium in their shells, and calcium is found in minerals in the earth. These forms of calcium are economical, and you can get as much as 500 mg to 600 mg in one tablet. However, there are concerns that the natural forms of calcium supplements may contain significant amounts of lead.2The level of contamination has decreased in recent years, but still may present a health risk.3,4 Calcium supplements rarely list the lead content of their source, although they should. The lead concentration should always be less than 2 parts per million.

Refined Calcium Carbonate

This is the most common commercial calcium supplement, and it is also used as a common antacid. Calcium carbonate is one of the least expensive forms of calcium, but it can cause constipation and bloating, and it may not be well absorbed by people with reduced levels of stomach acid. Taking it with meals improves absorption because stomach acid is released to digest the food.121 (See the section, Chelated Calcium, below.)

Chelated Calcium

Chelated calcium is calcium bound to an organic acid (citrate, citrate malate, lactate, gluconate, aspartate, or orotate). The chelated forms of calcium offer some significant advantages and disadvantages compared with calcium carbonate.

Certain forms of chelated calcium (calcium citrate and calcium citrate malate) are widely thought to be significantly better absorbed and more effective for osteoporosis treatment than calcium carbonate. However, while some studies support this belief,6,7,9,10others do not.8,122,123 The discrepancy may be due to the particular calcium carbonate products used; some calcium carbonate formulations may dissolve better than others.

One study found that calcium citrate malate in orange juice is markedly better absorbed than tricalcium phosphate/calcium lactate in orange juice.148

A form of calcium called active absorbable algal calcium (AAACa) has also been promoted as superior to calcium carbonate, but the study upon which claims of benefit are founded actually used quite questionable statistical methods (technically, post-hoc subgroup analysis).133

Chelated calcium is much more expensive and bulkier than calcium carbonate. In other words, you have to take larger pills, and more of them, to get enough calcium. It is not at all uncommon to need to take five or six large capsules daily to supply the necessary amount, a quantity some people may find troublesome.