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Other name(s):

calcium carbonate, calcium citrate, calcium glubionate, calcium gluconate, calcium lactate, calcium phosphate, tricalcium phosphate

General description

Calcium is the most abundant mineral in the human body and the major component in bone. Most calcium in the body is found in the bones in a mineral form called calcium hydroxyapatite.

Calcium is a fundamental building block of bone and tooth enamel. It is incorporated into bone and enamel as calcium hydroxyapatite and other related crystalline forms. Calcium is also essential for muscle contraction and relaxation. It plays a role in sending nerve impulses, controlling nerve irritability, and the clotting of blood. Calcium is also an enzyme cofactor that aids the endocrine and exocrine glands.

Medically valid uses

It is important to have enough calcium during periods of bone growth (childhood and adolescence), during pregnancy, when breastfeeding, and following menopause. Calcium is essential for the production of breast milk, and it is needed by the fetus for development. Too little calcium throughout puberty and as an adult may contribute to osteopenia and osteoporosis; both result in weak bones that fracture easily.

Unsubstantiated claims

Please note that this section reports on claims that have NOT yet been substantiated through scientific studies.

Calcium is claimed to decrease the incidence of colorectal cancer, help reduce cardiovascular disease risk, reduce high blood pressure, relieve menstrual symptoms, aid in weight management, and prevent premature labor and birth. Again, these claims are not supported in current research findings.

Recommended intake

As indicated below, calcium is measured in milligrams (mg). Calcium is absorbed in small intestine, however only part of the calcium consumed in foods or supplements is absorbed.

The RDA is the Recommended Dietary Allowance.



Infants (0 to 6 months)

200 mg

Infants (6 months to 1 year)

260 mg

Children (1 to 3 years)

700 mg

Children (4 to 8 years)

1,000 mg

Youth (9 to 18 years)

1,300 mg

Adults (females 19 to 50 years; males 19 to 70 years)

1,000 mg

Adults (70+ years)

1,200 mg


50 years and older

1,200 mg

Pregnant or lactating


18 years or younger

1,300 mg

19 to 50 years

1,000 mg

People with low stomach acid, such as the elderly, should consider taking calcium citrate since it is more easily absorbed than any other form of calcium.

Calcium is available in tablets ranging from 250 to 1,200 mg. It is also available in the form of chews, capsules, powders, wafers, and liquids.

Calcium exists in nature only in combination with other substances called compounds. These compounds contain different amounts of elemental calcium, which is the actual amount of calcium in the supplement. Calcium is found in many commercial preparations. Each form has a different percentage of calcium. Calcium carbonate and calcium phosphate contain the highest concentrations of calcium, with calcium gluconate and calcium glubionate containing the lowest.

Selected calcium-rich foods


Calcium (mg)

Fortified oatmeal, 1 packet


Sardines, canned in oil, with edible bones, 3 oz.


Cheddar cheese, 1.5 oz. shredded


Milk, nonfat, 1 cup


Milkshake, 1 cup


Yogurt, plain, low-fat, 1 cup


Soybeans, cooked, 1 cup


Tofu, firm, with calcium, 1/2 cup


Orange juice, fortified with calcium, 6 oz.

200–260 (varies)

Salmon, canned, with edible bones, 3 oz.


Pudding, instant (chocolate, banana, etc.) made with 2% milk, 1/2 cup


Baked beans, 1 cup


Cottage cheese, 1% milk fat, 1 cup


Spaghetti, lasagna, 1 cup


Frozen yogurt, vanilla, soft-serve, 1/2 cup


Ready-to-eat cereal, fortified with calcium, 1 cup

100–1,000 (varies)

Cheese pizza, 1 slice


Fortified waffles, 2


Turnip greens, boiled, 1/2 cup


Broccoli, raw, 1 cup


Ice cream, vanilla, 1/2 cup


Soy or rice milk, fortified with calcium, 1 cup

80–500 (varies)

Source: The 2004 Surgeon General’s Report on Bone Health and Osteoporosis: What It Means to You. U.S. Department of Health and Human Services, Office of the Surgeon General, 2004, pages 12–13.

Calcium is stable in foods and does not deteriorate with different types of storage or cooking.

Additional calcium is beneficial during the rapid growth spurts of infancy, childhood and adolescence, and for both adolescent and pre- and post-menopausal women. In addition, certain conditions call for increased calcium intake, including malabsorption syndromes such as sprue, celiac disease, pancreatitis, and cirrhosis. People who are lactose intolerant and those with milk allergies need alternative dietary sources of calcium.

People who consume moderate to heavy amounts of alcohol or caffeine, and people who are anorexic also need additional calcium.

Calcium, whether from food or supplements, is absorbed best by the body when it is taken several times a day in amounts of 500 mg or less, but taking it all at once is better than not taking it at all. Calcium carbonate is absorbed best when taken with food. Calcium citrate can be taken anytime.

Calcium supplements are used to treat calcium-deficient states such as tetany of the newborn, end-stage renal disease, renal insufficiency, hypoparathyroidism, pseudohypoparathyroidism, postmenopausal and senile osteoporosis, rickets and osteomalacia.

Chronic deficiency of calcium results in poor bone mineralization, and decreased bone growth and repair. In young adults, this may lead to osteomalacia (softening of the bone). In older adults and particularly post-menopausal women it may lead to osteoporosis (reduction in bone mass). In children, poor bone mineralization (usually related to vitamin D and calcium deficiency combined) is associated with rickets.

Tetany is a condition that occurs when the serum level of ionized calcium becomes too low and muscles contract and remain contracted. Tetany generally does not reflect a total-body calcium deficit but rather an acute decrease in ionized calcium in the blood (often as a result of hyperventilation).

Side effects, toxicity, and interactions

Exceptionally high calcium levels in the blood is called hypercalcemia.  It is uncommon to get too much calcium from foods; high blood levels are more likely to be brought on by calcium supplements. 

Excess calcium intake (approximately 2 grams or more), especially in association with excess vitamin D, may result in calcium deposits in muscles (causing stiffness and pain) and on heart valves (causing potentially fatal damage). In older adults, vitamin D intake in excess of 800 mcg/day should be avoided, especially when taking calcium supplements.

Consuming large amounts of calcium along with milk or an absorbable antacid (often used to treat hyperacidity or ulcers) can result in a condition known as milk-alkali syndrome. This can cause hypercalcemia and damage to the kidneys.

Do not take calcium supplements if your serum calcium levels are too high or your phosphate levels are too low (as determined by a physician). Do not take calcium supplements if you have kidney failure, are a pre-dialysis patient, or are taking thiazide-type diuretics (HCTZ, hydrochlorothiazide, indapamide).

Since calcium (from supplements, not food) may cause kidney stones, do not take calcium if you are prone to developing kidney stones.

Women who are pregnant or breastfeeding should consult a physician before taking any mineral supplements.

Calcium binds with the tetracycline family of antibiotics, inhibiting absorption of both the mineral and the drug. The same problem may occur with norfloxacin. Excess calcium may also decrease the effectiveness of verapamil. Calcium also reduces the absorption of iron from the gastrointestinal tract. You should not take a calcium supplement at the same time as an iron supplement—unless the calcium supplement is calcium citrate, or unless the iron supplement is taken with vitamin C. Any medication that you need to take on an empty stomach should not be taken with calcium supplements. Calcium competes for absorption with magnesium, iron, and zinc.  Calcium absorption may increase with high levels of vitamin D.

Additional information

Calcium is the most common and widely used supplement. It is the easiest one to use and promises a great benefit for women by preventing osteoporosis.

Over 40 million people in the United States today already have osteoporosis or are at elevated risk as a result of low bone mass. Conditions that make it more likely that a woman will develop osteoporosis often begin during adolescence. Thin or underweight young women are at risk for developing osteoporosis in later life. If an eating disorder such as anorexia nervosa is involved, the risk is even greater. Chronic dieting often impairs calcium intake and is likely to contribute to the incidence of osteoporosis. As an older adult, alcohol or caffeine consumption, or a diet deficient in calcium also contribute to the future development of osteoporosis.

Factors that protect against developing osteoporosis include maintaining normal weight (or being slightly overweight) during adolescence, and exercise (especially high-impact activities such as running and weight lifting). These activities should begin during adolescence and continue into adulthood. Early onset of the menses, late onset of menopause, and adequate intake of both calcium and vitamin D throughout life also help protect against osteoporosis.

Click here for a list of reputable websites with general information on nutrition.