Calcium is the most abundant mineral in the human body. Average healthy males contain about 2.5 to 3 pounds of calcium while females contain about 2 pounds. Approximately 99 percent of calcium is present in the bones and teeth, which leaves only about one percent in cells and body fluids.

Although only a small amount of calcium is in the blood, the body goes to great lengths to maintain blood-calcium levels within a relatively narrow range. Three regulatory mechanisms control blood-calcium. If levels drop too low, intestinal calcium absorption can increase, calcium can be released from bones, and/or the kidneys reduce calcium excretion. In bones and teeth, calcium exists primarily as hydroxyapatite, which is a calcium carbonate/calcium phosphate crystalline compound that provides rigidity and strength to these tissues.

Dosage Info

Dosage Range

Dosages that have been used in clinical studies range from 500-2,500mg daily. (1) , (2)

Most Common Dosage

1,200mg daily.

1000mg elemental calcium
= ~3,950mg calcium acetate
= ~2,500mg calcium carbonate
= ~3,700mg calcium chloride
= ~4,740mg calcium citrate
= ~11,110mg calcium gluconate
= ~7,690mg calcium lactate
= ~4,000mg microcrystalline hydroxyapatite compound (MCHC)
= ~3,450mg calcium phosphate, dibasic anhydrous
= ~4,350mg calcium phosphate, dibasic dihydrate
= ~2,500mg calcium phosphate, tribasic

Dosage Forms

Tablets, capsules, powder, chewable tablets, functional foods, liposomal sprays, and injections (Rx only).

Adult RDI


Adult ODA



  • Infants <6 months: 210mg (Adequate Intake, AI)
  • Infants 7-12 months: 270mg (AI)
  • Children 1-3 years: 500mg (AI)
  • Children 4-8 years: 800mg (AI)
  • Children 9-18 years: 1,300mg (AI)
  • Adults 19-50 years: 1,000mg (AI)
  • Adults >50 years: 1,200mg (AI)
  • Pregnancy 19 years: 1,000mg (AI)
  • Lactation 19 years: 1,000mg (AI)

Interactions and Depletions



Active Forms

Calcium citrate, aspartate, ascorbate, lactate, phosphate, carbonate, glycinate, malate, amino acid chelates, and microcrystalline hydroxyapatite compound (MCHC).


Calcium absorption in humans is regulated by a biological control system that depends on the following factors: a balance between calcium made available from bone resorption, intestinal absorption, and renal tubular reabsorption as well as the calcium lost to new skeletal formation and kidney and intestinal excretion. When calcium intake is low, the majority of calcium absorption is accomplished by an active transport mechanism in the duodenum. However, when calcium intake is high, passive absorption in the jejunum and ileum becomes the major absorptive process. A small amount of calcium absorption takes place in the large intestine by both active and passive processes.

Toxicities & Precautions


Large doses of calcium are efficiently excreted by the body and do not usually produce toxic effects unless the individual has a history of kidney stones.

Functions in the Body

Bones and Teeth

Most important function is in the development and maintenance of healthy bones and teeth. Need is greatest during periods of rapid growth including childhood, pregnancy, and lactation. (3) , (4)

Muscle Contraction

Helps to initiate muscle contractions. As such, it plays a vital role in the contraction-relaxation cycle that regulates a normal heartbeat.

Blood Clotting

Involved in several steps of the blood clotting mechanism.

Cell Wall Permeability

Regulates the passage of fluids across cellular membranes by affecting cell wall permeability.

Enzyme Function

Activates various enzyme systems responsible for muscle contraction, fat digestion, and protein metabolism.

Nerve Transmission

Plays a role in the regulation and transmission of nerve impulses.

Signal Messenger

Low extracellular calcium signals the release of parathyroid hormone, which increases calcium absorption.

Clinical Applications


In general, calcium supplementation in postmenopausal women slows, but does not arrest osteoporosis. (5)


Calcium supplementation after the 20th week of pregnancy reduces a woman’s risk of developing pregnancy-related hypertension. (6)

Blood Pressure Regulation

Low levels of calcium are associated with high blood pressure, and many studies have shown that calcium supplementation provides hypertensive patients with a slight lowering of blood pressure. However, the gains are so small that calcium cannot be suggested as a primary treatment. (7) , (8)

Kidney Stones

Calcium binds to oxalate, which reduces stone formation. (9) , (10)


In some cases, calcium supplementation provides a modest lowering of blood pressure. (11) , (12)

Cancer Prevention

Several studies report that men with low levels of calcium intake have higher rates of colorectal cancer. (13) Calcium supplementation in high-risk individuals also decreased the rate of abnormal cell division in the colon. (14) , (15)


Calcium supplementation is a simple and effective treatment in premenstrual syndrome, resulting in a major reduction in overall luteal phase symptoms. (16)

Elevated Cholesterol

1,200mg of calcium carbonate daily provided slight improvement, a 4.4 percent lowering of LDL and a 4.1 percent increase of HDL. (17)

Symptoms and Causes of Deficiency

There are three skeletal diseases associated with calcium deficiency. Rickets is the classical calcium deficiency disease. It occurs in children and causes a variety of bone deformities. When this condition develops in adults, it is called osteomalacia. Osteoporosis is associated with a lack of vitamin D, which causes a reduction in the absorption of calcium.

The symptoms of calcium deficiency include muscle cramps, heart palpitations, high blood pressure, brittle or soft bones, tooth decay, back and leg pains, insomnia, and nervous disorders.

    Osteoporosis and osteomalacia are the two main adult conditions caused by calcium deficiency. Bone deformities and fractures are the result. Magnesium deficiency causes various abnormalities in calcium metabolism. Ingestion of foods high in phosphorus (soft drinks and animal protein) promotes the urinary loss of calcium. Intestinal inflammatory conditions can decrease calcium absorption. Other significant factors that can negatively influence calcium levels include caffeine, excess dietary fat and fiber, and lack of exercise.

Dietary Sources

Milk and dairy products are the major source of dietary calcium for most people. Other good sources are dark green leafy vegetables, broccoli, legumes, nuts, and whole grains.


  1. View Abstract: Heaney RP. Calcium supplements: practical considerations. Osteoporos Int. Feb1991;1(2):65-71.
  2. View Abstract: Dawson-Hughes B, Harris SS, Krall EA, Dallal GE. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med. Sep1997;337(10):670-676.
  3. View Abstract: Abrams SA. Calcium turnover and nutrition through the life cycle. Proc Nutr Soc. May2001;60(2):283-9.
  4. View Abstract: O'Brien KO, Nathanson MS, Mancini J, Witter FR. Calcium absorption is significantly higher in adolescents during pregnancy than in the early postpartum period. Am J Clin Nutr. Dec2003;78(6):1188-93.
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  6. View Abstract: Belizan JM, et al. Calcium Supplementation to Prevent Hypertensive Disorders of Pregnancy. N Engl J Med. Nov1991;325(20):1399-405.
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  8. View Abstract: Cappuccio FP, et al. Oral Calcium Supplementation and Blood Pressure: An Overview of Randomized Controlled Trials. J Hypertens. Dec1989;7(12):941-46.
  9. Marshall RW, et al. Relationships Between Calcium and Oxalic Acid Intake in the Diet and Their Excretion in the Urine of Normal and Renal-stone-forming Subjects. Clin Sci. Jul1972;43(1):91-99.
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  11. View Abstract: Griffith LE, et al. The influence of dietary and nondietary calcium supplementation on blood pressure: an updated metaanalysis of randomized controlled trials. Am J Hypertens. Jan1999;12(1 Pt 1):84-92.
  12. View Abstract: Moore TJ. The Role of Dietary Electrolytes in Hypertension. J Am Coll Nutr. 1989;8:68S-80S.
  13. View Abstract: Garland CF, et al. Can Colon Cancer Incidence and Death Rates be Reduced with Calcium and Vitamin D? Am J Clin Nutr. Jul1991;54(1 Suppl):193S-201S.
  14. View Abstract: Rozen P, et al. Calcium supplements interact significantly with long-term diet while suppressing rectal epithelial proliferation of adenoma patients. Cancer. Feb2001;91(4):833-40.
  15. View Abstract: Rozen P, et al. Oral Calcium Suppresses Increased Rectal Epithelial Proliferation of Persons at Risk of Colorectal Cancer. Gut. May1989;30(5):650-55.
  16. View Abstract: Thys-Jacobs S, et al. Calcium Carbonate and the Premenstrual Syndrome: Effects on Premenstrual and Menstrual Symptoms. Premenstrual Syndrome Study Group. Am j Obstet Gynecol. Aug1998;179(2):444-52.
  17. View Abstract: Bell L, et al. Cholesterol-lowering Effects of Calcium Carbonate in Patients with Mild to Moderate Hypercholesterolemia. Arch Intern Med. Dec1992;152(12):2441-44.