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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 well-known role.

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):

Science Ratings Health Concerns

Gestational hypertension

Lactose intolerance (for preventing deficiency if dairy products are avoided only)


Preeclampsia (for deficiency)

Premenstrual syndrome



Celiac disease (for deficiency only)

High blood pressure

High cholesterol

High triglycerides

Pregnancy and postpartum support

Weight loss


Amenorrhea (calcium for preventing bone loss)

Colon cancer (reduces risk)


Dysmenorrhea (painful menstruation)

Gingivitis (periodontal disease)

Insulin resistance syndrome (Syndrome X)

Kidney stones

Migraine headaches

Multiple sclerosis

3Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

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 women.

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 their condition.

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 calcium.

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 multimineral supplement.

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 preparation.

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 the urine.10

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 osteoporosis.12

Are there any drug interactions?
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].

4. Heaney RP, Recker RR, Weaver CM. Absorbability of calcium sources: the limited role of solubility. Calcif Tissue Int 1990;46:300–4.

5. Levenson DI, Bockman RS. A review of calcium preparations. Nutr Rev 1994;52:221–32 [review].

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. JAMA 2000;284:1425–9.

9. Heaney RP, Nordin BEC. Calcium effects on phosphorus absorption: implications for the prevention and co-therapy of osteoporosis. J Am Coll Nutr 2002;21:239–44.

10. Kruger MC, Horrobin DF. Calcium metabolism, osteoporosis and 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.

12. Flodin NW. The metabolic roles; pharmacology, and toxicology of lysine. J Am Coll Nutr 1997;16:7–21 [review].

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