Clinician Fact Sheet: Calcium
Clinician Fact Sheet
Calcium
May 2001; Volume 4; S1-S2
Eight million American women and 2 million American men have osteoporosis. Another 18 million have low bone density, which increases their risk of osteoporosis. Although many Americans are aware of the role calcium plays in maintaining bone health, few receive recommended amounts of calcium from their diet. In recent years, our knowledge of the role of calcium in other diseases and conditions (e.g., colon cancer and premenstrual syndrome) has expanded, reinforcing the need for adequate calcium intakes.
Dietary Reference Intakes (DRI)
- 210 mg/d for children 0-6 mo
- 270 mg/d for children 7 mo-1 y
- 500 mg/d for children 1-3 y
- 800 mg/d for children 4-8 y
- 1300 mg/d for children 9-18 y
- 1000 mg/d for adults 19-50 y
- 1200 mg/d for adults 51 y and older
Food Sources
Dietary sources of calcium include dairy products, kale, broccoli, calcium-enriched citrus juices, mineral water, canned fish with bones, and tofu.
Mechanism of Action
- Bones and teeth contain more than 99% of the body’s calcium. Calcium in bone is a reserve source of calcium that can be mobilized to maintain extracellular calcium concentrations.
- Calcium is involved in intracellular regulation, enzyme activation, hormone secretion, initiation of DNA synthesis, and muscle cell function. In heart muscle and nerve terminals, calcium channels open when membranes are depolarized and stored calcium is released.
- Calcium is lost in varying amounts through the feces, urine, sweat, and sloughed skin cells.
Calcium Solubility, Bioavailability, and Absorption
- Although some studies have found calcium citrate to be more bioavailable and absorbable than calcium carbonate,1-3 these studies were performed on fasting patients, which can lead to erratic absorption.4 When ingested as part of a meal, calcium carbonate is equally well absorbed.5
- Calcium absorption is not determined exclusively by the solubility of the calcium salt, but varies with age, environmental and dietary conditions, vitamin D status, and race. Average absorption ranges from 25% in infants to 60% in young adults, and generally decreases throughout adulthood.
- Calcium exhibits threshold absorption. Below the threshold, increased calcium intake improves response; above the threshold, increased calcium intake has no effect. It is recommended that patients split doses above 600 mg.
- Calcium content of various preparations: carbonate, 40%; tricalcium phosphate, 38%; dicalcium phosphate, 31%; bone meal, 31%; oyster shell, 28%; dolomite, 22%; citrate, 21%; lactate, 13%; gluconate, 9%; glubionate, 6.5%.6
Clinical Uses
- To reduce the risk of colorectal cancer.
- To treat diarrhea and rectal epithelial hyperproliferation following intestinal bypass.
- To treat hypocalcemia, chronic hypoparathyroidism, and osteomalacia.
- To prevent and treat osteoporosis, rickets, and latent tetany.
- To bind phosphate in renal failure (calcium carbonate and calcium acetate).
- To treat indigestion (calcium carbonate).
- To reduce fluoride levels in children.
- To treat hypertension.
- To treat premenstrual syndrome.
- To increase fetal bone mineralization when taken by pregnant women with low dietary calcium intake.
- To prevent pregnancy-related hypertension and pre-eclampsia.
- To prevent ischemic stroke.
Adverse Effects/Toxicity
- Routine dietary intake and supplementation in recommended doses are not associated with significant adverse effects; however, gastrointestinal irritation, belching, flatulence, and constipation are common complaints.
- Calcium carbonate can cause acid rebound.
- Intakes exceeding 2 g/d can increase the risk of kidney stones and renal damage; this dose may be lower in patients with idiopathic hypercalciurea.
- Prolonged ingestion of large amounts (greater than 20 g/d) of calcium carbonate can cause hypercalcemia, milk-alkali syndrome, nephrocalcinosis, and renal insufficiency.
- Ingestion of calcium chloride may cause gastrointestinal hemorrhage.
- Epidemiological evidence suggests that high dietary calcium intake might increase the risk of prostate cancer.
Interactions/Nutrient Depletion
- Calcium absorption is increased by: concomitant administration of vitamin D and estrogen.
- Calcium absorption is decreased by: concomitant administration of fluoroquinolones and tetracyclines; mineral oil; stimulant laxatives; wheat bran; and high-phytate soybeans.
- Concomitant calcium administration decreases the absorption of: iron, zinc, magnesium, bisphosphonates, fluoroquinolones, thyroid hormones, and tetracyclines.
- Concomitant use of thiazide diuretics and moderately large amounts of calcium carbonate increase the risk of milk-alkali syndrome.
- Urinary calcium excretion is increased by: concomitant administration of thiazide diuretics; aluminum and magnesium salts; thyroid hormones; and high sodium intake.
- Pretreatment with intravenous calcium gluconate can prevent or reduce the hypotensive effects of intravenous verapamil without affecting the antiarrhythmic effects of verapamil.
- Use of corticosteroids can cause calcium depletion and osteoporosis.
- Calcium carbonate use can alter the results of: serum gastrin, serum lipase, and bone mineral density tests.
- Calcium gluconate use can alter the results of: serum glucose, plasma 11-hydroxycorticosteroids, urinary 17-hydroxycorticosteroids, plasma insulin, I-131 uptake, and serum magnesium tests.
- Hyperparathyroid activity predisposes individuals to increased calcium absorption.
- Calcium use in individuals with high serum phosphate levels should be monitored carefully to prevent precipitation of calcium phosphate and soft tissue calcification.
- Renal insufficiency predisposes individuals to reduced calcium absorption.
- Sarcoidosis results in increased risk of excessive calcium absorption and hypercalcemia.
- Smoking decreases calcium absorption.
References
1. NIH Consensus Development Panel on Optimal Calcium Intake. Optimal calcium intake. NIH Consensus conference. JAMA 1994;272:1942-1948.
2. Dawson-Hughes B, et al. A controlled trial of the effect of calcium supplementation on bone density in postmenopausal women. N Engl J Med 1990;323:878-883.
3. Harvey JA, et al. Superior calcium absorption from calcium citrate than calcium carbonate using external forearm counting. J Am Coll Nutr 1990;9:583-587.
4. Heaney RP, et al. Meal effects on calcium absorption. Am J Clin Nutr 1989;49:372-376.
5. Heaney RP, et al. Absorption of calcium as the carbonate and citrate salts, with some observations on method. Osteoporos Int 1999;9:19-23.
7. Levenson DI, Bockman RS. A review of calcium preparations. Nutr Rev 1994;52:221-232.
Resources
Alternative Therapies in Women’s Health. Atlanta, GA: American Health Consultants; 2000;4:25-32.
Pelton R, et al. Drug-Induced Nutrient Depletion Handbook. Hudson, OH: Lexi-Comp; 1999.
Natural Medicines Comprehensive Database [database online]. Stockton, CA: Therapeutic Research Center, Inc., 2000.
May 2001; Volume 4; S1-S2
Subscribe Now for Access
You have reached your article limit for the month. We hope you found our articles both enjoyable and insightful. For information on new subscriptions, product trials, alternative billing arrangements or group and site discounts please call 800-688-2421. We look forward to having you as a long-term member of the Relias Media community.