Calcium supplement
500 milligram calcium supplements made from calcium carbonate
Clinical data
Trade namesAlka-Mints, Calcet, Tums, others
License data
Routes of
By mouth, intravenous
ATC code
CAS Number
  • none

Calcium supplements are salts of calcium used in a number of conditions.[1] Supplementation is generally only required when there is not enough calcium in the diet.[2][3] By mouth they are used to treat and prevent low blood calcium, osteoporosis, and rickets.[1] By injection into a vein they are used for low blood calcium that is resulting in muscle spasms and for high blood potassium or magnesium toxicity.[2][4]

Common side effects include constipation and nausea.[1] When taken by mouth high blood calcium is uncommon.[1] Calcium supplements, unlike calcium from dietary sources, appear to increase the risk of kidney stones.[1] Adults generally require about a gram of calcium a day.[1] Calcium is particularly important for bones, muscles, and nerves.[1]

The medical use of calcium supplements began in the 19th century.[5] It is on the World Health Organization's List of Essential Medicines.[6] It is available as a generic medication.[3] In 2021, it was the 235th most commonly prescribed medication in the United States, with more than 1 million prescriptions.[7][8] Versions are also sold together with vitamin D.[3] In 2020, the combination, calcium/vitamin D was the 215th most commonly prescribed medication in the United States, with more than 2 million prescriptions.[9][10]

Health effects

Bone health

In healthy people, calcium supplementation is not necessary for maintaining bone mineral density, and carries risks that outweigh any benefits.[11] Calcium intake is not significantly associated with hip fracture risk in either men or women.[12] The US Preventive Service Task Force recommends against a daily supplement of calcium or vitamin D.[13][14] Although a slight increase in bone mineral density occurred in healthy children from calcium supplementation, using additional dietary calcium is not justified, according to a 2006 review.[15]

Cardiovascular impact

There is good evidence that 1,000 mg to 1,500 mg of daily calcium supplementation can effect a modest reduction in blood pressure in adults who do not have a blood pressure condition, suggesting that achieving adequate calcium levels may have role in preventing high blood pressure.[16]


The US National Cancer Institute does not recommend the use of calcium supplements for lowering the risk of cancer.[17] There is weak evidence calcium supplementation might have a preventative effect against developing colorectal adenomatous polyps, but the evidence is not sufficient to recommend such supplementation.[18]

Side effects

Excessive consumption of calcium carbonate antacids/dietary supplements (such as Tums) over a period of weeks or months can cause milk-alkali syndrome, with symptoms ranging from hypercalcemia to potentially fatal kidney failure. What constitutes "excessive" consumption is not well known and, it is presumed, varies a great deal from person to person. Persons consuming more than 10 grams/day of calcium carbonate (4 grams of elemental calcium) are at risk of developing milk-alkali syndrome,[19] but the condition has been reported in at least one person consuming only 2.5 grams/day of calcium carbonate (1 gram of elemental calcium), an amount usually considered moderate and safe.[20]

A 2023 systematic review found that calcium supplementation is not associated with myocardial infarction, stroke, heart failure admission, and cardiovascular/all-cause mortality.[21]

Calcium supplements may contribute to the development of kidney stones.[1]

Acute calcium poisoning is rare, and difficult to achieve without administering calcium intravenously. For example, the oral median lethal dose (LD50) for rats for calcium carbonate and calcium chloride are 6.45[22] and 1.4 g/kg,[23] respectively.


Calcium supplements by mouth diminish the absorption of thyroxine when taken within four to six hours of each other.[24] Thus, people taking both calcium and thyroxine run the risk of inadequate thyroid hormone replacement and thence hypothyroidism if they take them simultaneously or near-simultaneously, because significant amount of T4 is adsorbed to calcium carbonate depending on gastric pH levels, preventing absorption of T4 at the intestinal level.[25][24]


Calcium absorption in the gut is influenced by factors such as vitamin D levels, gut acidity, age, estrogen levels, and dietary fiber intake. It decreases with age, low vitamin D levels, hypochlorhydria, low estrogen levels, and a high-fiber diet. Calcium is absorbed both actively and passively in the small intestines, with low vitamin D levels impairing active absorption. Calcium absorption varies with serum 25-hydroxyvitamin D [25(OH)D] levels and is also influenced by dietary factors and genetics. Individuals vary in their ability to absorb calcium, with absorption inversely related to total dietary calcium intake, dietary fiber, alcohol intake, and physical activity, and positively associated with body mass index, dietary fat intake, and serum 1,25(OH2)D and parathyroid hormone levels.[26]


Calcium is excreted from the human body primarily through urine and feces. Several factors can influence the rate of urinary calcium loss, including the intake of caffeine, protein, and sodium and low estrogen levels. Caffeine intake has been associated with bone loss, particularly in women aged 66-77 years. Women consuming more than 300 mg of caffeine per day usually experience greater bone loss in the spine than those consuming less than or equal to 300 mg per day. Genetic variants of the Vitamin D Receptor (VDR) also play a role.[26]


The intravenous formulations of calcium include calcium chloride and calcium gluconate.[1] The forms that are taken by mouth include calcium acetate, calcium carbonate, calcium citrate, calcium gluconate, calcium lactate, and calcium phosphate.[1]

Vitamin D is added to some calcium supplements. Proper vitamin D status is important because vitamin D is converted to a hormone in the body, which then induces the synthesis of intestinal proteins responsible for calcium absorption.[49]


For US dietary supplement and food labeling purposes, the amount in a serving is expressed in milligrams and as a percent of Daily Value (%DV). The labels indicate the weight of the elemental calcium in the supplement, not the total weight of the compound. For instance, in the case of calcium citrate, the label specifies the weight of the elemental calcium, not the entire calcium citrate compound. For calcium labeling purposes 100% of the Daily Value was 1000 mg, but in May 2016 it was revised to 1000–1300 mg.[50] A table of the pre-change adult Daily Values and references for the revision are provided at Reference Daily Intake. Food and supplement companies had until July 2018 to comply with the labeling change.[50]


  1. ^ a b c d e f g h i j "Calcium Salts". The American Society of Health-System Pharmacists. Archived from the original on 18 January 2017. Retrieved 8 January 2017.
  2. ^ a b World Health Organization (2009). Stuart MC, Kouimtzi M, Hill SR (eds.). WHO Model Formulary 2008. World Health Organization. p. 497. hdl:10665/44053. ISBN 978-92-4-154765-9.
  3. ^ a b c British national formulary : BNF 69 (69 ed.). British Medical Association. 2015. pp. 694, 703. ISBN 978-0-85711-156-2.
  4. ^ Hamilton R (2015). Tarascon Pocket Pharmacopoeia 2015 Deluxe Lab-Coat Edition. Jones & Bartlett Learning. pp. 215–216. ISBN 978-1-284-05756-0.
  5. ^ Tegethoff FW (2012). Calcium Carbonate: From the Cretaceous Period into the 21st Century. Birkhäuser. p. 308. ISBN 978-3-0348-8245-3. Archived from the original on 16 January 2017.
  6. ^ World Health Organization (2019). World Health Organization model list of essential medicines: 21st list 2019. Geneva: World Health Organization. hdl:10665/325771. WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO.
  7. ^ "The Top 300 of 2021". ClinCalc. Archived from the original on 15 January 2024. Retrieved 14 January 2024.
  8. ^ "Calcium - Drug Usage Statistics". ClinCalc. Archived from the original on 8 July 2020. Retrieved 14 January 2024.
  9. ^ "The Top 300 of 2020". ClinCalc. Archived from the original on 23 June 2023. Retrieved 7 October 2022.((cite web)): CS1 maint: unfit URL (link)
  10. ^ "Calcium; Vitamin D – Drug Usage Statistics". ClinCalc. Archived from the original on 5 June 2023. Retrieved 7 October 2022.
  11. ^ Reid IR, Bristow SM, Bolland MJ (October 2015). "Calcium supplements: benefits and risks". Journal of Internal Medicine (Review). 278 (4): 354–368. doi:10.1111/joim.12394. PMID 26174589. S2CID 4679930.
  12. ^ Bischoff-Ferrari HA, Dawson-Hughes B, Baron JA, Burckhardt P, Li R, Spiegelman D, et al. (December 2007). "Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomized controlled trials". The American Journal of Clinical Nutrition. 86 (6): 1780–1790. doi:10.1093/ajcn/86.5.1780. PMID 18065599.
  13. ^ Moyer VA (May 2013). "Vitamin D and calcium supplementation to prevent fractures in adults: U.S. Preventive Services Task Force recommendation statement". Annals of Internal Medicine. 158 (9): 691–696. doi:10.7326/0003-4819-158-9-201305070-00603. PMID 23440163. S2CID 23008867.
  14. ^ "Recommendation: Vitamin D, Calcium, or Combined Supplementation for the Primary Prevention of Fractures in Community-Dwelling Adults: Preventive Medication". United States Preventive Services Taskforce. 17 April 2018. Archived from the original on 4 March 2024. Retrieved 4 March 2024.
  15. ^ Winzenberg TM, Shaw K, Fryer J, Jones G (April 2006). "Calcium supplementation for improving bone mineral density in children". The Cochrane Database of Systematic Reviews. 2006 (2): CD005119. doi:10.1002/14651858.CD005119.pub2. PMC 8865374. PMID 16625624.
  16. ^ Cormick G, Ciapponi A, Cafferata ML, Cormick MS, Belizán JM (January 2022). "Calcium supplementation for prevention of primary hypertension". The Cochrane Database of Systematic Reviews (Systematic review). 1 (1): CD010037. doi:10.1002/14651858.CD010037.pub4. PMC 8748265. PMID 35014026.
  17. ^ "Calcium and Cancer Prevention: Strengths and Limits of the Evidence". National Cancer Institute. 4 May 2009. Archived from the original on 29 November 2014. Retrieved 2 November 2014.
  18. ^ Weingarten MA, Zalmanovici A, Yaphe J (January 2008). "Dietary calcium supplementation for preventing colorectal cancer and adenomatous polyps". The Cochrane Database of Systematic Reviews (Review). 2008 (1): CD003548. doi:10.1002/14651858.CD003548.pub4. PMC 8719254. PMID 18254022.
  19. ^ Beall DP, Henslee HB, Webb HR, Scofield RH (May 2006). "Milk-alkali syndrome: a historical review and description of the modern version of the syndrome". The American Journal of the Medical Sciences. 331 (5): 233–242. doi:10.1097/00000441-200605000-00001. PMID 16702792. S2CID 45802184.
  20. ^ Picolos MK, Orlander PR (2005). "Calcium carbonate toxicity: the updated milk-alkali syndrome; report of 3 cases and review of the literature". Endocrine Practice. 11 (4): 272–280. doi:10.4158/EP.11.4.272. PMID 16006300.
  21. ^ Sim MG, Teo YN, Teo YH, Syn NL, Li TY, Yeo LL, et al. (September 2023). "Association Between Calcium Supplementation and the Risk of Cardiovascular Disease and Stroke: A Systematic Review and Meta-Analysis". Heart, Lung & Circulation. 32 (10): S1443–9506(23)04281–6. doi:10.1016/j.hlc.2023.07.008. PMID 37743221. S2CID 262224167.
  22. ^ Lewis RJ (1996). Sax's Dangerous Properties of Industrial Materials (9th ed.). New York, NY: Van Nostrand Reinhold. p. 635. ISBN 978-0-471-37858-7.
  23. ^ ITII. Toxic and Hazardous Industrial Chemicals Safety Manual. Tokyo, Japan: The International Technical Information Institute. 1988. p. 101.
  24. ^ a b Singh N, Singh PN, Hershman JM (June 2000). "Effect of calcium carbonate on the absorption of levothyroxine". JAMA. 283 (21): 2822–2825. doi:10.1001/jama.283.21.2822. PMID 10838651.
  25. ^ Virili C, Antonelli A, Santaguida MG, Benvenga S, Centanni M (2019). "Gastrointestinal Malabsorption of Thyroxine". Endocrine Reviews. 40 (1): 118–136. doi:10.1210/er.2018-00168. hdl:11568/936596. PMID 30476027. Archived from the original on 23 February 2024. Retrieved 15 March 2024.
  26. ^ a b c d e f g h i j k l m Straub DA (June 2007). "Calcium supplementation in clinical practice: a review of forms, doses, and indications". Nutr Clin Pract. 22 (3): 286–96. doi:10.1177/0115426507022003286. PMID 17507729.
  27. ^ Weaver CM (2006). "29 Calcium". In Bowman BA, Russell RM (eds.). Present Knowledge in Nutrition. Vol. I (9th ed.). ILSI Press. p. 377. ISBN 978-1-57881-198-4.
  28. ^ Shkembi B, Huppertz T (2021). "Calcium Absorption from Food Products: Food Matrix Effects". Nutrients. 14 (1): 180. doi:10.3390/nu14010180. PMC 8746734. PMID 35011055.
  29. ^ Hunt C, Nielsen F (2009). "Nutritional Aspects of Minerals in Bovine and Human Milks". Advanced Dairy Chemistry. pp. 391–456. doi:10.1007/978-0-387-84865-5_10. ISBN 978-0-387-84864-8.
  30. ^
  31. ^ "Office of Dietary Supplements - Calcium".
  32. ^ a b Fritz K, Taylor K, Parmar M (2024). Calcium Carbonate. PMID 32965974.
  33. ^ Remington J (2005). Remington: The Science and Practice of Pharmacy. Lippincott Williams & Wilkins. p. 1338. ISBN 978-0-7817-4673-1.
  34. ^ Zhao Y, Martin BR, Weaver CM (October 2005). "Calcium bioavailability of calcium carbonate fortified soymilk is equivalent to cow's milk in young women" (PDF). The Journal of Nutrition. 135 (10): 2379–2382. doi:10.1093/jn/135.10.2379. PMID 16177199. Archived (PDF) from the original on 18 September 2017.
  35. ^ Martini L, Wood RJ (December 2002). "Relative bioavailability of calcium-rich dietary sources in the elderly". The American Journal of Clinical Nutrition. 76 (6): 1345–1350. doi:10.1093/ajcn/76.6.1345. PMID 12450902.
  36. ^ "Office of Dietary Supplements - Calcium". Archived from the original on 17 March 2018. Retrieved 15 March 2024.
  37. ^ White CM (March 2022). "Lead in Mineral or Multivitamin-Multimineral Products". Ann Pharmacother. 56 (3): 339–345. doi:10.1177/10600280211023328. PMID 34096339.
  38. ^ a b Castelo-Branco C, Ciria-Recasens M, Cancelo-Hidalgo MJ, Palacios S, Haya-Palazuelos J, Carbonell-Abelló J, et al. (2009). "Efficacy of ossein-hydroxyapatite complex compared with calcium carbonate to prevent bone loss: a meta-analysis". Menopause. 16 (5): 984–91. doi:10.1097/gme.0b013e3181a1824e. PMID 19407667.
  39. ^ Maton PN, Burton ME (1999). "Antacids Revisited". Drugs. 57 (6): 855–870. doi:10.2165/00003495-199957060-00003. PMID 10400401. Archived from the original on 20 April 2023. Retrieved 15 March 2024.
  40. ^ Garg V, Narang P, Taneja R (2022). "Antacids revisited: Review on contemporary facts and relevance for self-management". Journal of International Medical Research. 50 (3). doi:10.1177/03000605221086457. PMC 8966100. PMID 35343261.
  41. ^ a b c Straub DA (June 2007). "Calcium supplementation in clinical practice: a review of forms, doses, and indications". Nutrition in Clinical Practice. 22 (3): 286–296. doi:10.1177/0115426507022003286. PMID 17507729.
  42. ^ Martin BR, Weaver CM, Heaney RP, Packard PT, Smith DL (June 2002). "Calcium absorption from three salts and CaSO(4)-fortified bread in premenopausal women". Journal of Agricultural and Food Chemistry. 50 (13): 3874–3876. doi:10.1021/jf020065g. PMID 12059174.
  43. ^ a b Bendich A (January 2001). "Calcium supplementation and iron status of females". Nutrition. 17 (1): 46–51. doi:10.1016/s0899-9007(00)00482-2. PMID 11165888.
  44. ^ "Calcium Chloride: Indications, Side Effects, Warnings". Archived from the original on 17 February 2023. Retrieved 15 March 2024.
  45. ^
  46. ^ Remes-Troche JM (2013). "A 'black stomach' due to ingestion of anhydrous calcium chloride". BMJ Case Reports. 2013: bcr2012007716. doi:10.1136/bcr-2012-007716. PMC 3604345. PMID 23283618.
  47. ^ Hagiwara Y, Seki K, Takahashi Y (2020). "Oral chemical burn due to accidental ingestion of calcium oxide food desiccant in a patient with dementia". Journal of International Medical Research. 48 (4). doi:10.1177/0300060520920065. PMC 7223204. PMID 32338100.
  48. ^ Nakagawa Y, Maeda A, Takahashi T, Kaneoka Y (2020). "Gastric Necrosis because of Ingestion of Calcium Chloride". ACG Case Reports Journal. 7 (8): e00446. doi:10.14309/crj.0000000000000446. PMC 7447462. PMID 32903978.
  49. ^ Combs G (2008). The Vitamins. Academic Press. p. 161. ISBN 978-0-12-183490-6.
  50. ^ a b "". Archived from the original on 5 December 2022. Retrieved 18 January 2023.