Calcium is the most abundant, essential mineral in the human body. Of the two to three
pounds of calcium contained in the average body, 99% is located in the bones and teeth.
Calcium is needed to form bones and teeth and is also required for blood clotting,
transmission of signals in nerve cells, and muscle contraction. The importance of calcium for
preventing osteoporosis is probably its most
Warning: Calcium supplements should be avoided by prostate cancer patients.
Where is it found?
Most dietary calcium comes from dairy
products. The myth that calcium from dairy products is not absorbed is not supported by
scientific research.1 2 Other good sources include sardines, canned salmon, green leafy vegetables, and tofu.
Calcium has been used in
connection with the following conditions (refer to the individual
health concern for complete information):
Who is likely to be deficient?
Severe deficiency of either calcium or vitamin
D leads to a condition called rickets in
children and osteomalacia in adults. Since
vitamin D is required for calcium absorption, people with conditions causing vitamin D
deficiency (e.g., pancreatic insufficiency) may develop a deficiency of calcium as well.
Vegans (pure vegetarians), people with dark
skin, those who live in northern climates, and people who stay indoors almost all the time are
more likely to be vitamin D deficient than are other people. Vegans often eat less calcium and
vitamin D than do other people. Most people eat well below the recommended amount of calcium.
This lack of dietary calcium is thought to contribute to the risk of osteoporosis, particularly in white and Asian
How much is usually taken?
The National Academy of Sciences has established guidelines for calcium that are
25–50% higher than previous recommendations. For ages 19 to 50, calcium intake is
recommended to be 1,000 mg daily; for adults over age 51, the recommendation is 1,200 mg
daily.3 The most common supplemental amount for adults is 800–1,000 mg per
day.4 General recommendations for higher daily intakes (1,200–1,500 mg)
usually include the calcium most people consume from their diets. Studies indicate the average
daily amount of calcium consumed by Americans is about 500–1,000 mg.
Are there any side effects or interactions?
Constipation, bloating, and gas are sometimes reported with the use of calcium
supplements.5 A very high intake of calcium from dairy products plus supplemental calcium carbonate was
reported in the past to cause a condition called “milk alkali syndrome.” This
toxicity is rarely reported today because most medical doctors no longer tell people with ulcers to use this approach as treatment for
People with hyperparathyroidism, chronic kidney disease, or kidney stones should not supplement with calcium
without consulting a physician. For other adults, the highest amount typically suggested by
doctors (1,200 mg per day) is considered quite safe. People with prostate cancer should avoid supplementing with
In the past, calcium supplements in the forms of bone meal (including MCHC), dolomite, and
oyster shell have sometimes had higher lead levels than permitted by stringent California
regulations, though generally less than the levels set by the federal government.6
“Refined” forms (which would include CCM, calcium citrate, and most calcium
carbonate) have low levels.7 More recently, a survey of over-the-counter calcium
supplements found low or undetectable levels of lead in most products,8
representing a sharp decline in lead content of calcium supplements since 1993. People who
decide to take bone meal, dolomite, oyster shell, or coral calcium for long periods of time
can contact the supplying supplement company to request independent laboratory analysis
showing minimal lead levels.
Some studies have shown that calcium competes for absorption with a number of other
minerals, while other studies have found no such competition. To be on the safe side, some
doctors recommend that people taking calcium for long periods of time should also take a
One study has shown that taking calcium can interfere with the absorption of phosphorus,
which, like calcium, is important for bone health.9 . Although most western diets
contain ample or even excessive amounts of phosphorus, older people who supplement with large
amounts of calcium may be at risk of developing phosphorus deficiency. For this reason, the
authors of this study recommend that, for elderly people, at least some of the supplemental
calcium be taken in the form of tricalcium phosphate or some other phosphorus-containing
Vitamin D’s most important role is
maintaining blood levels of calcium. Therefore, many doctors recommend that those
supplementing with calcium also supplement with 400 IU of vitamin D per day.
Animal studies have shown that essential fatty acids (EFAs) increase calcium absorption
from the gut, in part by enhancing the effects of vitamin D and reducing loss of calcium in
Lysine supplementation increases the
absorption of calcium and may reduce its excretion.11 As a result, some researchers
believe that lysine may eventually be shown to have a role in the prevention and treatment of
Are there any drug
Certain medicines may interact with calcium. Refer to drug interactions for a list of those medicines.
1. Sheikh MS, Santa Ana CA, Nicar MJ, et al. Gastrointestinal absorption
of calcium from milk and calcium salts. N Engl J Med 1987;317:532–6.
2. Levenson DI, Bockman RS. A review of calcium preparations. Nutr
Rev 1994;52:221–32 [review].
3. Standing Committee on the Scientific Evaluation of Dietary Reference
Intakes, Food and Nutrition Board, Institute of Medicine. Dietary reference intakes for
calcium, phosphorus, magnesium, vitamin D and fluoride. Washington DC: National Academy
Press, 1997, 108–17 [review].
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limited role of solubility. Calcif Tissue Int 1990;46:300–4.
5. Levenson DI, Bockman RS. A review of calcium preparations. Nutr
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6. Burros M. Testing calcium supplements for lead. New York
Times June 4, 1997, B7.
7. Bourgoin BP, Evans DR, Cornett JR, et al. Lead content in 70 brands of
dietary calcium supplements. Am J Public Health 1993;83:1155–60.
8. Ross EA, Szabo NJ, Tebbett IR. Lead content of calcium supplements.
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implications for the prevention and co-therapy of osteoporosis. J Am Coll Nutr
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essential fatty acids: a review. Prog Lipid Res 1997;36:131–51 [review].
11. Civitelli R, Villareal DT, Agnusdei D, et al. Dietary L-lysine and
calcium metabolism in humans. Nutrition 1992;8:400–5.
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lysine. J Am Coll Nutr 1997;16:7–21 [review].