Requirements and Supplementation

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Dietary calcium requirements depend in part upon whether the body is growing or making new bone or milk. Requirements are therefore greatest during childhood, adolescence, pregnancy, and breastfeeding. Recommended daily intake (of elemental calcium) varies accordingly: 400 mg for

Calcium supplements can help prevent osteoporosis, which is a condition that occurs when bone breaks down more quickly than it is replaced. In this illustration, the bone above is normal, but the bone below is more porous and therefore more susceptible to fracture. [Custom Medical Stock Photo, Inc. Reproduced by permission.]

Calcium supplements can help prevent osteoporosis, which is a condition that occurs when bone breaks down more quickly than it is replaced. In this illustration, the bone above is normal, but the bone below is more porous and therefore more susceptible to fracture. [Custom Medical Stock Photo, Inc. Reproduced by permission.]

infants 0-6 months, 600 mg for infants 6-12 months, 800 mg for children 1-10 years, 1,200 mg for ages 11-24 years, and 800 mg for individuals over 24 years of age. Pregnant women require additional calcium (RDA 1,200 mg). Many experts believe that elderly persons should take as much as 1,500

mg to help prevent osteoporosis, a common condition in which bones be- osteoporosis: weakening of the bone come weak and fracture easily due to a loss of bone density. Dairy products, structure meats, and some seafood (sardines, oysters) are excellent sources of calcium.

Spinach, beet greens, beans, and peanuts are among the best plant-derived sources.

Calcium absorption is affected by many factors, including age, the amount needed, and what foods are eaten at the same time. In general,



Elemental calcium by weight


Calcium carbonate

• Less well absorbed In persons with decreased stomach acid (e.g., elderly or those on anti-acid medicines)

• Natural preparations from oyster shell or bone meal may contain contaminants such as lead

• Least expensive

Calcium citrate


• Better absorbed, especially by those with decreased stomach acid

• May protect against kidney stones

• More expensive.

Calcium phosphate

38%% or 31%

• Tricalcium or dicalcium phosphate

• Absorption similar to calcium carbonate

Calcium gluconate


• Used intravenously for severe hypocalcemia

• Well absorbed orally, but low content of elemental calcium

• Very expensive

Calcium glubionate


• Available as syrup for children

• Low content elemental calcium.

Calcium lactate


• Well absorbed, but low content elemental calcium.

SOURCE: Gregory, Philip J

(2000) "Calcium Salts." Prescriber's Letter. Document #160313.

growth spurts: periods of rapid growth fat: type of food molecule rich in carbon and hydrogen, with high energy content intestines: the two long tubes that carry out the bulk of the processes of digestion fiber: indigestible plant material which aids digestion by providing bulk pH: level of acidity, with low numbers indicating high acidity acidity: measure of the tendency of a molecule to lose hydrogen ions, thus behaving as an acid hypertension: high blood pressure cancer: uncontrolled cell growth cardiovascular: related to the heart and circulatory system obesity: the condition of being overweight, according to established norms based on sex, age, and height stroke: loss of blood supply to part of the brain, due to a blocked or burst artery in the brain calcium from food sources is better absorbed than calcium taken as supplements. Children absorb a higher percentage of their ingested calcium than adults because their needs during growth spurts may be two or three times greater per body weight than adults. Vitamin D is necessary for intestinal absorption, making Vitamin D-fortified milk a very well-absorbed form of calcium. Older persons may not consume or make as much vitamin D as is optimal, so their calcium absorption may be decreased. Vitamin C and lactose (the sugar found in milk) enhance calcium absorption, whereas meals high in fat or protein may decrease absorption. Excess phosphorous consumption (as in carbonated sodas) can decrease calcium absorption in the intestines. High dietary fiber and phytate (a form of phytic acid found in dietary fiber and the husks of whole grains) may also decrease dietary calcium absorption in some areas of the world. Intestinal pH also affects calcium absorption—absorption is optimal with normal stomach acidity generated at meal times. Thus, persons with reduced stomach acidity (e.g., elderly persons, or persons on acid-reducing medicines) do not absorb calcium as well as others do.

Calcium supplements are widely used in the treatment and prevention of osteoporosis. Supplements are also recommended, or are being investigated, for a number of conditions, including hypertension, colon cancer, cardiovascular disease, premenstrual syndrome, obesity, stroke, and pre-eclampsia (a complication of pregnancy). There are several forms of calcium salts used as supplements. They vary in their content of elemental calcium, the amount effectively absorbed by the body, and cost. Whatever the specific form, the supplement should be taken with meals to maximize absorption.

Calcium is one of the most important macronutrients for the body's growth and function. Sufficient amounts are important in preventing many diseases. Calcium levels are tightly controlled by a complex interaction of hormones and vitamins. Dietary requirements vary throughout life and are greatest during periods of growth and pregnancy. However, recent reports suggest that many people do not get sufficient amounts of calcium in their diet. Various calcium supplements are available when dietary intake is inadequate. see also Minerals; Osteomalacia; Osteoporosis; Rickets.

Donna Staton Marcus Harding


Berkow, Robert, ed. (1997). The Merck Manual of Medical Information, Home Edition. Whitehouse Station, NJ: Merck & Co.

National Research Council (1989). Recommended Dietary Allowances, 10th edition. Washington, DC: National Academy Press.

Olendorf, Donna; Jeryan, Christine; and Boyden, Karen, eds. (1999). The Gale Encyclopedia of Medicine. Farmington Hills, MI: Gale Research.

Internet Resources

Food and Nutrition Board (1999). Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press. Available from <>

Gregory, Philip J. (2000) "Calcium Salts." Prescriber's Letter Document #160313. Available from <>

vitamin: necessary complex nutrient used to aid enzymes or other metabolic processes in the cell

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