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calcium

What can high-calcium foods do for you?

  • Maintain healthy, strong bones
  • Support proper functioning of nerves and muscles
  • Help your blood clot

What events can indicate a need for more high-calcium foods?

  • Frequent bone fractures
  • Muscle pain or spasms
  • Tingling or numbness in your hands and feet
  • Bone deformities and growth retardation in children

Excellent sources of calcium include spinach, turnip greens, mustard greens, and collard greens.

Description

What is calcium?

One of the most abundant minerals in the human body, calcium accounts for approximately 1.5% of total body weight. Bones and teeth house 99% of the calcium in the body, while the remaining 1% is distributed in other areas.

In recent years, consumers have been bombarded with public health messages encouraging the consumption of foods rich in calcium. These messages are aimed at preventing osteoporosis, a disease characterized by brittle and porous bones that now affects more than 20 million individuals in the United States. A calcium-deficient diet is one of the causative factors of osteoporosis.

Our food ranking system - based on nutrient density - shows spinach, turnip greens, mustard greens, and collard greens to be excellent sources of calcium. Our ranking system looks not only at the amount of calcium in food, but also at the caloric content of food and how many calories of a food are necessary to provide the desired amount of calcium. Dairy foods - which are often listed as excellent sources of calcium - turn out to be very good sources of calcium in our ranking system (just one step below turnip greens, and mustard greens) because of their lower nutrient density.

How it Functions

Calcium is best known for its role in maintaining the strength and density of bones. In a process known as bone mineralization, calcium and phosphorous join to form calcium phosphate. Calcium phosphate is a major component of the mineral complex (called hydroxyapatite) that gives structure and strength to bones.

Calcium also plays a role in many physiological activities not related to bones including blood clotting, nerve conduction, muscle contraction, regulation of enzyme activity, and cell membrane function. Because these physiological activities are essential to life, the body utilizes complex regulatory systems to tightly control the amount of calcium in the blood so that calcium is available for these activities. As a result, when dietary intake of calcium is too low to maintain normal blood levels of calcium, the body will draw on calcium stores in the bones to maintain normal blood concentrations, which, after many years, can lead to osteoporosis.

Deficiency Symptoms

Insufficient calcium intake, poor calcium absorption, and/or excessive calcium losses through the urine and feces can cause calcium deficiency. In children, calcium deficiency can cause improper bone mineralization, which leads to rickets, a condition characterized by bone deformities and growth retardation. In adults, calcium deficiency may result in osteomalacia, or “softening of the bone”. Calcium deficiency, along with other contributing factors, can also result in osteoporosis.

Low levels of calcium in the blood (especially one particular form of calcium, called free ionized calcium) may cause a condition called tetany, in which nerve activity becomes excessive. Symptoms of tetany include muscle pain and spasms, as well as tingling and/or numbness in the hands and feet.

Toxicity Symptoms

Excessive intakes of calcium (more than 3,000 mg per day) may result in elevated blood calcium levels, a condition known as hypercalcemia. If blood levels of phosphorous are low at the same time as calcium levels are high, hypercalcemia can lead to soft tissue calcification. This condition involves the unwanted accumulation of calcium in cells other than bone. A Tolerable Upper Intake Level (UL) for calcium of 2,500 milligrams per day was established by the National Academy of Sciences in 1997.

Impact of Cooking, Storage and Processing

The amount of calcium in foods is not adversely impacted by cooking or long-term storage.

Factors that Affect Function

Hypochlorhydria, a condition characterized by insufficient secretion of stomach acid, affects many people and is especially common in the elderly. Lack of stomach acid impairs the absorption of calcium and may lead to poor calcium status.

Adequate intake of vitamin D is necessary for the absorption and utilization of calcium. As a result, vitamin D deficiency, or impaired conversion of the inactive to the active form of vitamin D (which takes place in the liver and kidneys), may also lead to a poor calcium status.

Drug-Nutrient Interactions

The following medications impact the absorption, utilization, and/or excretion of calcium:

  • The corticosteroids (for example, hydrocortisone and prednisone) are a family of anti-inflammatory drugs that are commonly used in the treatment of autoimmune and inflammatory diseases such as asthma, rheumatoid arthritis, and ulcerative colitis. These drugs reduce the body’s ability to activate vitamin D, resulting in decreased calcium absorption and increased calcium excretion in the urine.
  • Aluminum-containing antacids, including Maalox (TM) and Mylanta (TM), may increase the urinary and stool loss of calcium.
  • Thyroid hormones may increase urinary excretion of calcium.
  • Anticonvulsant medications, including Dilantin (TM), are used to control seizure activity in people with epilepsy and brain cancer, and those who have suffered head trauma through injury or stroke. Such medications decrease the activity of vitamin D, resulting in decreased calcium absorption.
  • Certain antibiotics, including gentamicin, erythromycin, neomycin, isoniazid, sulfamethoxazole, tobramycin,and cycloserine, may interfere with calcium absorption and/or utilization.
  • Hormone replacement therapy may decrease calcium excretion and increase calcium absorption in postmenopausal women.

Calcium, especially from supplements, can interfere with the absorption of the following medications:

  • Alendronate (Fosamax (TM)) is used in the treatment and prevention of osteoporosis. Calcium supplements may interfere with alendronate absorption.
  • Since most people who take alendronate also take calcium supplements, it is advisable to take the alendronate at least two hours before or after taking the calcium supplement.
  • Calcium from antacids, dairy products, and supplements can decrease the absorption of tetracycline antibiotics, thereby reducing the effectiveness of these drugs.

Nutrient Interactions

The following nutrients impact the absorption, utilization and/or excretion of calcium:

  • Vitamin D accelerates the absorption of calcium from the gastrointestinal tract.
  • High consumption of potassium reduces the urinary excretion of calcium.
  • High intakes of sodium, caffeine, or protein cause an increase in the urinary excretion of calcium.
  • Certain types of dietary fiber like the fiber found in wheat and oat bran, may interfere with calcium absorption by decreasing transit time (the amount of time it takes for digested foods to move through the intestines), limiting the amount of time during digestion for calcium to be absorbed. Dietary fiber also stimulates the proliferation of “friendly” bacteria in the gut, which bind calcium and make it less available for absorption.
  • Phytic acid, found in whole grains, nuts, and legumes, can bind to calcium to form and insoluble complex, thereby decreasing the absorption of calcium.
  • Oxalic acid, found in spinach, beets, celery, pecans, peanuts, tea and cocoa, can bind to calcium and form an insoluble complex that is excreted in the feces. While research studies confirm the ability of phytic acid and oxalic acid in foods to lower availability of calcium, the decrease in available calcium is relatively small.

Calcium impacts the absorption of the following nutrients:

  • Calcium in food and supplements decreases the absorption of heme and nonheme iron.
  • Magnesium and calcium compete with each other for intestinal absorption. Consequently, calcium supplements should not be taken at the same time as magnesium supplements.

Health Conditions

What health conditions require special emphasis on calcium?

Calcium may play a role in the prevention and/or treatment of the following health conditions:

  • Cataracts
  • Colon cancer
  • High blood pressure
  • Inflammatory bowel disease
  • Kidney stones
  • Osteoporosis
  • Polycystic ovarian syndrome
  • Pregnancy induced hypertension and preeclampsia
  • Premenstrual syndrome

Form in Dietary Supplements

Supplemental calcium is available in a variety of delivery forms including tablets, capsules, chewable tablets, antacids (for example, Tums(TM)) and fortified juices. Some dietary supplement manufacturers even sell chewy chocolate squares fortified with calcium. The different forms of calcium used in the manufacture of calcium supplements fall into three general categories: 1) naturally-derived calcium 2) refined calcium carbonate and 3) chelated calcium. Naturally-derived calcium, also known as unrefined calcium carbonate, appears in dietary supplements as bone meal, oyster shell, limestone, and dolomite (clay). Although these forms are typically less expensive than other forms of supplemental calcium, these supplements may also contain significant amounts of lead, a toxic metal that affects the brain, kidney, and red blood cells. Refined calcium carbonate is the most commonly used form of calcium in supplements. It is relatively inexpensive compared to chelated forms of calcium, but has been shown to be less well-absorbed than other forms. To improve absorption, calcium carbonate should be taken with meals, as the presence of food in the stomach causes the secretion of hydrochloric (stomach) acid, a compound that breaks down calcium carbonate. Chelated calcium is calcium bound to an organic acid, such as citrate, malate, lactate, or gluconate; or to an amino acid, such as aspartate. Research indicates that calcium chelates, especially calcium citrate, are more bioavailable than calcium carbonate. Calcium is also available as hydroxyapatite, the phosphorus-containing building block of the bone mineral matrix.

Food Sources

Introduction to Nutrient Rating System Chart

The following chart shows the foods which are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving; the nutrient density rating; and the food's World's Healthiest Foods Rating. Not all of our Daily Value standards are obtained from the FDA. In most instances, we used FDA Daily Values when available because they are widely recognized and apply to both men and women. However, when unavailable, we've used other science-based research to establish nutritional standards. Underneath the chart is a table that summarizes how the ratings were devised. Read more about our Nutrient Rating System.

Foods Ranked as quality sources of:
calcium
Food Serving
Size
Cals Amount
(mg)
DV
(%)
Nutrient
Density
World's
Healthiest
Foods Rating
Basil, Ground 2 tsp 7.5 63.40 6.3 15.2 very good
Greens, Turnip, Cooked 1 cup 28.8 197.28 19.7 12.3 excellent
Thyme, Ground 2 tsp 7.9 54.16 5.4 12.3 very good
Spinach (boiled, with salt) 1 cup 41.4 244.80 24.5 10.6 excellent
Oregano, Ground 2 tsp 9.2 47.28 4.7 9.3 good
Dill Seed 2 tsp 13.4 66.69 6.7 8.9 very good
Greens, Mustard, Boiled 1 cup 21.0 103.60 10.4 8.9 excellent
Cinnamon, Ground 2 tsp 11.8 55.68 5.6 8.5 very good
Collard Greens, Boiled, Drained 1 cup 49.4 226.10 22.6 8.2 excellent
Rosemary, Dried 2 tsp 7.3 28.16 2.8 7.0 good
Parsley, Fresh 1 oz-wt 10.2 39.12 3.9 6.9 good
Blackstrap Cane Molasses 2 tsp 32.1 117.53 11.8 6.6 very good
Peppermint Leaves, Fresh 1 oz-wt 19.9 68.89 6.9 6.2 very good
Chard, Boiled 1 cup 35.0 101.50 10.2 5.2 very good
Yogurt, Cow Milk, Low Fat 1 cup 155.1 447.37 44.7 5.2 very good
Lettuce, Romaine 2 cup 15.7 40.32 4.0 4.6 good
Kale, Fresh, Boiled 1 cup 36.4 93.60 9.4 4.6 very good
Mozzarella Cheese, Part Skim, Shredded 1 oz-wt 72.1 183.06 18.3 4.6 very good
Celery, Raw 1 cup 19.2 48.00 4.8 4.5 good
Milk, Cow, 2% 1 cup 121.2 296.70 29.7 4.4 very good
Cloves, Ground 2 tsp 14.2 28.40 2.8 3.6 good
Milk, Goat 1 cup 167.9 325.74 32.6 3.5 very good
Broccoli (pieces, steamed) 1 cup 43.7 74.72 7.5 3.1 good
Seeds, Sesame 0.25 cup 206.3 351.00 35.1 3.1 good
Fennel Bulb, Sliced, Raw 1 cup 27.0 42.64 4.3 2.8 good
Cabbage (shredded, boiled) 1 cup 33.0 46.50 4.7 2.5 good
Squash, Summer, All Varieties 1 cup 36.0 48.60 4.9 2.4 good
Green Snap/String Beans, Boiled 1 cup 43.8 57.50 5.8 2.4 good
Garlic 1 oz-wt 42.2 51.31 5.1 2.2 good
Tofu, Raw 4 oz-wt 86.2 100.00 10.0 2.1 good
Seeds, Mustard 2 tsp 35.0 38.92 3.9 2.0 good
Brussels Sprouts, Boiled 1 cup 60.8 56.16 5.6 1.7 good
Oranges 1 each 61.6 52.40 5.2 1.5 good
Asparagus, Boiled 1 cup 43.2 36.00 3.6 1.5 good
Mushrooms, Crimini, Raw 5 oz-wt 31.2 25.52 2.6 1.5 good
World's Healthiest
Foods Rating
Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%

Public Health Recommendations

In 1998, the Institute of Medicine at the National Academy of Sciences issued new Adequate Intake (AI) levels for calcium. The recommendations are as follows:

  • 0-6 months: 210 mg
  • 6-12 months: 270 mg
  • 1-3 years: 500 mg
  • 4-8 years: 800 mg
  • 9-13 years: 1300 mg
  • 14-18 years: 1300 mg
  • 19-30 years: 1000 mg
  • 31-50 years: 1000 mg
  • 51+ years: 1200 mg
  • Postmenopausal women not taking hormone replacement therapy: 1500 mg
  • Pregnant and lactating women (younger than 18 years): 1300 mg
  • Pregnant and lactating women (older than 18 years): 1000 mg

References

  • Bell L, et al. Cholesterol-lowering effects of calcium carbonate in patients with mild to moderate hypercholesterolemia. Arch Intern Med 1992;152:2441-2444.
  • Bostick RM, et al. Effect of calcium supplementation on serum cholesterol and blood pressure. Arch Fam Med 2000; 9:31-39.
  • Buckley LM, et al. Calcium and vitamin D3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. Ann Intern Med 1996; 125:961-968.
  • Cappuccio FP, et al. Epidemiologic association between dietary calcium intake and blood pressure: a meta-analysis of published data. Am J Epidemiol 1995;142:935-945.
  • Cook JD, Dassenko SA, Whittaker P. Calcium supplementation: effect on iron absorption. Am J Clin Nutr 1991;53:106-11.
  • Garland CF, Garland FC, Gorham ED. Calcium and vitamin D: Their potential roles in colon and breast cancer prevention. Ann N Y Acad Sci 1999;889:107-19.
  • Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995.
  • Hallberg L. Does calcium interfere with iron absorption. Am J Clin Nutr 1998;63:3-4.
  • Lee SJ, Kanis JA. An association between osteoporosis and premenstrual symptoms and postmenopausal symptoms. Bone and Mineral 1994;24:127-134.
  • Lininger SW, et al. A-Z guide to drug-herb-vitamin interactions. Prima Health, Rocklin, CA, 2000.
  • Miller JZ, et al. Calcium absorption from calcium carbonate and a new form of calcium (CCM) in healthy male and female adolescents. Am J Clin Nutr 1988;48:1291-4.
  • Minihane AM, et al. Effect of calcium supplementation on daily nonheme-iron absorption and long-term iron status. Am J Clin Nutr 1998;68:96-102.
  • Sakhaee K, Bhuket T, et al. Meta-analysis of calcium bioavailability: A comparison of calcium citrate with calcium carbonate. American Journal of Therapeutics 1999;6:313-321.
  • Thys-Jacobs S, Starkey P, Bernstein D, Tian J. Calcium carbonate and the premenstrual syndrome: effects on premenstrual and menstrual symptoms. Premestrual syndrome study group. Am J Obstet Gynecol 1998;179(2): 444-52.
  • Weaver CM, Proulx WR, Heaney R. Choices for achieving adequate dietary calcium with a vegetarian diet. Am J Clin Nutr 1999;70(suppl):543S-8S.
  • Wu K, Willet WC, Fuchs CS et al. Calcium intake and risk of colon cancer in women and men. J Natl Cancer Inst 2002 Mar 20;94(6):437-46.

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This page was updated on: 2004-11-21 10:56:10

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