What does calcium do?

Calcium is the most abundant 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.

Although calcium plays at least some minor role in lower blood pressure, the mechanisms involved appear complex and remain somewhat unclear.

By reducing absorption of oxalate, a substance found in many foods, calcium may be able to indirectly reduce the risk of kidney stones. However, people with a history of kidney stones must talk with a doctor before supplementing calcium, because such supplements might actually increase the risk of forming stones for the small number of people who absorb too much calcium.

Calcium also appears to partially bind some fats and cholesterol in the gastrointestinal tract. Perhaps as a result, some older research suggests that calcium supplements may help lower cholesterol levels.

Where is calcium found?

Most dietary calcium comes from dairy. The myth that calcium from dairy “doesn’t absorb” is not supported by scientific research.Other good sources include sardines, canned salmon, green leafy vegetables, and tofu.

Choosing a form of calcium supplement can be confusing. While fewer pills of the calcium carbonate form are needed, this form doesn’t absorb as well as some other forms of calcium. Most, but not all, studies suggest that calcium citrate is better absorbed than calcium carbonate. Virtually all comparative studies find that calcium citrate/malate (CCM) absorbs somewhat better than calcium carbonate. CCM is increasingly the form of calcium recommended by nutritionally oriented doctors. The microcrystaline hydroxyapatite (MCHC), a variation on the bonemeal form of calcium has been shown to improve bone mass but the absorption of MCHC appears to be poor. Only preliminary research exists regarding the amino acid chelates of calcium, and conclusions cannot be drawn at this time. Please refer to Calcium: Which Form is Best? for more information about choosing a calcium supplement.

Who is likely to be calcium deficient?

Severe deficiency of both calcium and vitamin D is called rickets in children and osteomalacia in adults. 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 others. 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 calcium is usually taken?

The National Academy of Sciences has established guidelines for calcium that are 25–50% higher than previous recommendations. For ages nineteen to fifty, calcium intake is recommended to be 1,000 mg daily; for adults over age fifty-one, the recommendation is 1,200 mg daily. The most common supplemental amount for adults is 800–1,000 mg per day. General recommendations for higher intakes (1,200–1,500 mg) usually include the several hundred milligrams of calcium most people consume from their diets.

Are there any side effects or interactions?

Constipation, bloating, and gas are sometimes reported with the use of calcium supplements. A very high intake of calcium from dairy taken with calcium carbonate used 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 take this combination.

People with hyperparathyroidism, or chronic kidney disease should not supplement with calcium without consulting a nutritionally oriented physician. People who have had kidney stones should read the section on kidney stones before considering supplements. For other adults, the highest amount typically suggested by nutritionally oriented doctors (1,200 mg per day) is considered quite safe.

In some cases, calcium supplements in the forms of bonemeal (including MCHC), dolomite, and oyster shell have higher lead levels than permitted by California regulations, though generally less than the levels set by the federal government. “Refined” forms (which would include CCM, calcium citrate, and most calcium carbonate) had low levels. In that report, only bonemeal exceeded federal levels. People who decide to take bonemeal, dolomite, or oyster shell for long periods of time should contact the supplying supplement company to request independent laboratory analysis showing minimal lead levels.

Vitamin D is needed for calcium to absorb. Therefore, many nutritionally oriented doctors recommend that those supplementing with calcium also supplement with 400 IU of vitamin D per day.

Calcium competes for absorption with a number of other minerals. Therefore, individuals taking calcium for more than a few weeks should also take a multimineral supplement.

Lysine supplements increase the absorption of calcium and may reduce its excretion. As a result some researchers believe that lysine may eventually be shown to have a role in the prevention and treatment of osteoporosis.

Information on this site is provided for informational purposes and is not meant to substitute for the advice provided by a licensed physician. You should not use the information on this website for diagnosing or treating a health problem or disease, or prescribing any medication.