What does it do?
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.
Although calcium plays at least some minor role in lowering blood pressure, the mechanisms involved appear complex and
somewhat unclear.1 The level of calcium in the blood is tightly regulated by
parathyroid hormone (PTH), and low intake of calcium causes elevations in PTH, which in turn
have been implicated in the development of
hypertension.2 High calcium intake has also been associated with a reduced risk
of cardiovascular disease in postmenopausal women.3
By reducing absorption of oxalate,4 a substance found in many foods, calcium may
be able to indirectly reduce the risk of kidney
stones.5 However, people with a history of kidney stones must talk with a
doctor before supplementing with calcium because such supplementation 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 research
suggests that calcium supplementation may help lower cholesterol levels.6
Animal studies have established a role of calcium in the development of female egg cells
(oocytes).7 8 Although the precise role of calcium is unclear, some
researchers speculate that future studies may identify important uses for calcium in
conditions of the human ovary, such as polycystic ovary syndrome (PCOS).9
Through a variety of mechanisms, calcium may have
anticancer actions within the colon. Most preliminary studies have shown high calcium
diets are associated with reduced colon cancer
risk.10 Most,11 12 13 but not all,14
preliminary studies have found taking calcium supplements to also be associated with a reduced
risk of colon cancer or precancerous conditions in the colon. One preliminary study reported
that high dietary, but not supplemental, calcium intake was associated with a decreased risk
of precancerous changes in the colon.15 In double-blind studies, calcium
supplementation has significantly protected against precancerous changes in the colon in
some,16 17 but not all, studies.18 19
Warning: Calcium supplements should be avoided by prostate cancer patients.
Are there any side effects or interactions?
Constipation, bloating, and gas are sometimes reported with the use of calcium
supplements.24 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.25
“Refined” forms (which would include CCM, calcium citrate, and most calcium
carbonate) have low levels.26 More recently, a survey of over-the-counter calcium
supplements found low or undetectable levels of lead in most products,27
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.
Calcium competes for absorption with a number of other minerals. Therefore, people taking
calcium for more than a few weeks 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.28 . 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.29
Lysine supplementation increases the absorption of calcium
and may reduce its excretion.30 As a result, some researchers believe that lysine
may eventually be shown to have a role in the prevention and treatment of osteoporosis.31
Are there any drug
interactions?
Certain medicines may interact with calcium. Refer to
drug interactions for a list of those medicines.
References
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