What does it 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 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 older 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 Most11 12 13 but not all14 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
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.20 21 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, some people may not absorb this form of calcium as well as some other forms. Most,22 23 but not all,24 studies suggest that calcium citrate is better absorbed than calcium carbonate. Virtually all comparative studies find that calcium citrate/malate (CCM) is absorbed somewhat better than calcium carbonate. CCM is increasingly the form of calcium recommended by doctors. Microcrystalline hydroxyapatite (MCHC), a variation on the bone meal form of calcium, has been shown to improve bone mass,25 but the absorption of MCHC appears to be poor.26 27 Only preliminary research exists regarding the amino acid chelates of calcium, and conclusions cannot be drawn at this time.
Calcium has been used in connection with the following conditions (refer to the individual health concern for complete information):
Lactose intolerance (for preventing deficiency if dairy products are avoided only)
Preeclampsia (for deficiency)
disease (for deficiency only)
High blood pressure
(calcium for preventing bone loss)
Colon cancer (reduces risk)
Dysmenorrhea (painful menstruation)
Gingivitis (periodontal disease)
Insulin resistance syndrome (Syndrome X)
Pregnancy and postpartum support
Warning: Calcium supplements should be avoided by prostate cancer patients.
Reliable and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
An herb is primarily supported by traditional use, or the herb or supplement has 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.28 The most common supplemental amount for adults is 800–1,000 mg per day.29 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.30 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.
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.31 “Refined” forms (which would include CCM, calcium citrate, and most calcium carbonate) have low levels.32 More recently, a survey of over-the-counter calcium supplements found low or undetectable levels of lead in most products,33 representing a sharp decline in lead content of calcium supplements since 1993. People who decide to take bone meal, dolomite, or oyster shell 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.
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.34
Lysine supplementation increases the absorption of calcium and may reduce its excretion.35 As a result, some researchers believe that lysine may eventually be shown to have a role in the prevention and treatment of osteoporosis.36
Are there any drug interactions? Certain medications may interact with calcium. Refer to the drug interactions safety check for a list of those medications.
1. Osborne CG, McTyre RB, Dudek J, et al. Evidence for the relationship of calcium to blood pressure. Nutr Rev 1996;54:365–81.
2. Jorde R, Sundsfjord J, Haug E, Bønaa KH. Relation between low calcium intake, parathyroid hormone, and blood pressure. Hypertension 2000;35:1154–9.
3. Bostick RM, Kushi LH, Wu Y, et al. Relation of calcium, vitamin D, and dairy food intake to ischemic heart disease mortality among postmenopausal women. Am J Epidemiol 1999;149:151–61.
4. Barilla DE, Notz C, Kennedy D, Pak CYC. Renal oxalate excretion following oral oxalate loads in patients with ileal disease and with renal and absorptive hypercalciurias: effect of calcium and magnesium. Am J Med 1978;64:579–85.
5. Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833–83.
6. Bell L, Halstenson CE, Halstenson CJ, et al. Cholesterol-lowering effects of calcium carbonate in patients with mild to moderate hypercholesterolemia. Arch Intern Med 1992;152:2441–4.
7. Homa ST, Carroll J, Swann K. The role of calcium in mammalian oocyte maturation and egg activation. Hum Reprod 1993;8:1274–81.
8. Kaufman M, Homa ST. Defining a role for calcium in the resumption and progression of meiosis in the pig oocyte. J Exp Zool 1993;265:69–76.
9. Thys-Jacobs S, Donovan D, Papadopoulos A, et al. Vitamin D and calcium dysregulation in the polycystic ovarian syndrome. Steroids 1999;64:430–5.
10. Lipkin M, Newmark H. Calcium and the prevention of colon cancer. J Cell Biochem Suppl 1995;22:65–73 [review].
11. Whelan RL, Horvath KD, Gleason NR, et al. Vitamin and calcium supplement use is associated with decreased adenoma recurrence in patients with a previous history of neoplasia. Dis Colon Rectum 1999;42:212–7.
12. White E, Shannon JS, Patterson RE. Relationship between vitamin and calcium supplement use and colon cancer. Cancer Epidemiol Biomarkers Prev 1997;6:769–74.
13. Kampman E, Slattery ML, Caan B, Potter JD. Calcium, vitamin D, sunshine exposure, dairy products and colon cancer risk (United States). Cancer Causes Control 2000;11:459–66.
14. Neugut AI, Horvath K, Whelan RL, et al. The effect of calcium and vitamin supplements on the incidence and recurrence of colorectal adenomatous polyps. Cancer 1996;78:723–8.
15. Hyman J, Baron JA, Dain BJ, et al. Dietary and supplemental calcium and the recurrence of colorectal adenomas. Cancer Epidemiol Biomarkers Prev 1998;7:291–5.
16. Baron JA, Beach M, Mandel JS, et al. Calcium supplements for the prevention of colorectal adenomas. N Engl J Med 1999;340:101–7.
17. Bostick RM, Fosdick L, Wood JR, et al. Calcium and colorectal epithelial cell proliferation in sporadic adenoma patients: a randomized, double-blinded, placebo-controlled clinical trial. J Natl Cancer Inst 1995;87:1307–15.
18. Cats A, Kleibeuker JH, van der Meer R, et al. Randomized, double-blinded, placebo-controlled intervention study with supplemental calcium in families with hereditary nonpolyposis colorectal cancer. J Natl Cancer Inst 1995;87:598–603.
19. Baron JA, Tosteson TD, Wargovich MJ, et al. Calcium supplementation and rectal mucosal proliferation: a randomized controlled trial. J Natl Cancer Inst 1995;87:1303–7.
20. 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.
21. Levenson DI, Bockman RS. A review of calcium preparations. Nutr Rev 1994;52:221–32 [review].
22. Nicar MJ, Pak CYC. Calcium bioavailability from calcium carbonate and calcium citrate. J Clin Endocrinol Metabol 1985;61:391–3.
23. Harvey JA, Kenny P, Poindexter J, Pak CYC. Superior calcium absorption from calcium citrate than calcium carbonate using external forearm counting. J Am Coll Nutr 1990;9:583–7.
24. 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.
25. Epstein O, Kato Y, Dick R, Sherlock S. Vitamin D, hydroxyapatite, and calcium gluconate in treatment of cortical bone thinning in postmenopausal women with primary biliary cirrhosis. Am J Clin Nutr 1982;36:426–30.
26. Heaney RP, Recker RR, Weaver CM. Absorbability of calcium sources: the limited role of solubility. Calcif Tissue Int 1990;46:300–4.
27. Deroisy R, Zartarian M, Meurmans L, et al. Acute changes in serum calcium and parathyroid hormone circulating levels induced by the oral intake of five currently available calcium salts in healthy male volunteers. Clin Rheumatol 1997;16:249–53.
28. 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].
29. Heaney RP, Recker RR, Weaver CM. Absorbability of calcium sources: the limited role of solubility. Calcif Tissue Int 1990;46:300–4.
30. Levenson DI, Bockman RS. A review of calcium preparations. Nutr Rev 1994;52:221–32 [review].
31. Burros M. Testing calcium supplements for lead. New York Times June 4, 1997, B7.
32. 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.
33. Ross EA, Szabo NJ, Tebbett IR. Lead content of calcium supplements. JAMA 2000;284:1425–9.
34. Kruger MC, Horrobin DF. Calcium metabolism, osteoporosis and essential fatty acids: a review. Prog Lipid Res 1997;36:131–51 [review].
35. Civitelli R, Villareal DT, Agnusdei D, et al. Dietary L-lysine and calcium metabolism in humans. Nutrition 1992;8:400–5.
36. Flodin NW. The metabolic roles; pharmacology, and toxicology of lysine. J Am Coll Nutr 1997;16:7–21 [review].
Copyright © 2002 VitaminLore, Inc. All rights reserved. www.VitaminLore.com
The information presented in VitaminLore Online is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over-the-counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2006.