Calcium Information: Forms of Calcium, Deficiency, Absorption

The most abundant mineral in the human body is calcium; the average male has roughly three pounds of calcium and the average female has roughly two pounds. Most calcium (99%) is found in the bones and teeth (National Research Council, 1989; Whitney et al, 1996) with the remaining 1% found in the soft tissues and watery parts of the body, where calcium helps to regulate normal processes of the body (Whitney et al, 1996).

According to Sourer, 1995; Whitney et al, 1996; Sizer et al, 1997, calcium functions include:

  • Construction, formation and maintenance of bone and teeth. This function helps reduce the occurrence of osteoporosis.
  • Blood clotting systems and, also, helps in wound healing.
  • Controlling blood pressure, nerve transmission and release of neurotransmitters.
  • Acting as an essential component in the production of enzymes and hormones that regulate digestion, energy and fat metabolism.
  • Transporting ions (electrically charged particles) across the membrane.
  • Muscle contraction.
  • Maintaining all cells and connective tissues in the body.

Forms of Calcium

There are two types of calcium: One type is tightly bound within the bone and the other more accessible type of calcium is found on the bone. The skeleton serves as a bank of minerals for the body. The body can borrow from the skeletal stores when blood calcium levels drop and return calcium to bones as needed.

A constant supply of calcium is necessary throughout our lifetime, but is especially important during phases of growth, pregnancy and lactation (breast feeding). About 10-40% of dietary calcium is absorbed in the small intestine with the help of vitamin D (Somer, 1995; Mahan et al, 1996). The level of calcium absorption from dietary sources drops to 7 in postmenopausal women (Sourer, 1995). The body will absorb more calcium if there is a deficiency.

There are many forms of calcium supplements currently available, such as calcium carbonate, calcium citrate, calcium gluconate, oyster shell, scallop shell, eggshell, milk products and, the latest, coral calcium. While there has been much debate over which type is best, it is clear that whatever form is taken, it needs to be absorbed by the body to provide any benefit.

Calcium Absorption

Calcium may be helpful to reduce the incidence of premature heart disease, especially if adequate intakes of magnesium are, also, maintained, and it may help to prevent periodontal disease (gum disease). Factors that improve calcium absorption are adequate amounts of protein, magnesium, phosphorous and vitamin D. There are a variety of drugs that impair or interfere with the absorption of calcium (drugs that interfere), so more calcium might be required to compensate.

Calcium Deficiency

Calcium deficiency in conjunction with high sodium intake is related to a higher risk of hypertension. Calcium deficiency can lead to loss of calcium from the bone (initially from the jaw and the backbone), which can lead to deformity and can cause extreme nerve sensitivity, muscle spasms and leg cramps (called tetany) (Sourer, 1995, McCarron et al, 1987; McCarron et al, 1991). Calcium deficiency can increase risk of bone disorders, such as osteoporosis. Conditions that reduce calcium absorption, which can lead to calcium deficiency, are:

  • High or excessive intake of oxalates and phytates, found in foods such as spinach and unleavened whole wheat products.
  • Consumption of alcohol, coffee, sugar or medications such as diuretics, tetracycline, aluminum containing antacids or stress.
  • Lack of exercise can reduce calcium absorption, as well as cause an increase in calcium losses.

More about Calcium Research Results

Here are a few more facts about calcium as discovered through various research activities:

  • Calcium, magnesium, zinc, fluoride and phosphorous work together to form and maintain bones and teeth (Somer, 1995; Mahan et al, 1996).
  • The ratio of calcium to phosphorous and calcium to magnesium are important in the absorption, use, and excretion of these minerals (Somer, 1995; Mahan et al, 1996).
  • Optimal calcium absorption depends on adequate amounts of vitamin D to be available (Somer, 1995; Mahan et al, 1996).
  • Calcium competes with magnesium, copper, zinc and manganese for intestinal absorption (Somer, 1995).
  • Calcium requirements go up in the presence of excess dietary protein, fat or phosphorous (phosphorous is abundant in most carbonated soda drinks) (Somer, 1995).
  • Calcium citrate increases absorption of aluminum from foods whereas other types of calcium reduce aluminum and lead absorption. (Somer, 1995).
  • Calcium may help control blood pressure by working against the negative effects of sodium chloride (Somer, 1995; Mahan et al, 1996).
  • The ratio of calcium to magnesium plays a role in heart disease development (Somer, 1995).

Dietary Sources of Calcium

Sources of calcium include milk and milk products, such as low-fat and nonfat cheese, cottage cheese, and yogurt. Lactose (sugar found in milk products), aids in calcium absorption in infants, but probably is not required in adults (Mahan et al, 1996). Other sources of calcium include these calcium rich foods: dark green leafy vegetables, spinach, kale, turnip greens, cabbage, collard, mustard, seaweeds, alfalfa, broccoli, canned fish (especially sardines, clams, oysters, and salmon with bones) and cooked dried beans and peas.

Lactose-intolerant people or those allergic to cow's milk and dairy products can get an adequate supply of calcium from dry green leafy vegetables.

Watch for Substandard Coral

Do not buy "Cheap Coral". It is not a bargain. Genuine Coral is expensive to harvest, ship and process properly. The stores and many web sites are filled with brands that cut corners such as:
  • Blending the Okinawa coral with other forms of calcium or coral from other parts of the world.
  • Selling low-grade coral or high-lead-content coral.
  • Selling it in caplet form, which is not absorbable due to binding agents and fillers. Capsules are much better utilized by humans.

Calcium Toxicity

As with many things, more is not necessarily better. Calcium is no exception to that rule, and if you consume too much calcium, especially if that calcium is through calcium supplements, negative results can occur. For instance:

  • Very large doses (several grams) of calcium may cause blood calcium levels to rise and lead to calcium deposits in soft tissue, such as the heart and kidney (Somer, 1995).
  • Large intakes of calcium may reduce zinc and iron absorption and impair vitamin K metabolism (Somer, 1995; Gregor, 1988).
  • Very high blood levels of calcium can cause heart or lung failure. Calcium ascorbate or calcium citrate are safe, less toxic sources than those from oyster shell, which may have lead levels that exceed the amount considered safe for children (Whiting, 1994).
  • Calcium-citrate-malate is a well-absorbed form of supplementary calcium (Smith, 1987).

Research shows that skeletal diseases such as osteomalacia (softening of the bones), osteoporosis (porous, fragile bones, with decreased bone density, which can result in spontaneous fractures) although caused by a calcium deficiency, does not respond to calcium therapy alone. Research conducted in Paris, France by noted biophysicist Louis Kervan, and in the United States by Dr. Richard Barmakian shows that fractured bones did not heal at all when high amounts of calcium were present. They heal fair to poorly when moderate amounts of calcium are present. But they heal extremely well when relatively low amounts of calcium are present with an abundance of silica.


  • Recommended Dietary Allowances. Subcommittee on the Tenth Edition of the RDA's Food and Nutrition Board Commission on Life Sciences. National Research Council: 10th Edition, Washington, DC: National Academy Press; 1989a; 174-184.
  • Whitney EN, Rolfes SR. Water and the Major Minerals. In: Understanding Nutrition. Seventh Edition, St. Paul, MN: West Publishing Company; 1996; 448-454.
  • Somer E. Minerals. In: The Essential Guide to Vitamins and Minerals, New York, NY Harper Perennial: New; 1995; 89-94.
  • Mahan LK and Escott-Stump S. Minerals In: Krause's Food, Nutrition and Diet Therapy, 9th Edition, Philadelphia, PA. WB. Saunders Company, 1996; 124-130.
  • Sizer F. and Whitney E. Water and Minerals, In: Nutrition Concepts and Controversies 7th Edition. Belmont, CA; Wadsworth Publishing Co;1997;292-295. McCarron D, Morris C, Bukoski R. 1987. "The calcium paradox of essential hypertension." Am J Med 82:27-33.
  • McCarron K, Reusser M. 1991. "The integrated effects of electrolytes on blood pressure." Nutr Rep 9:57,62,64.
  • Dietary Reference Intakes (DRI), Institute of Medicine, Food and Nutrition Board, based on Adequate Intakes (AI) National Academy of Sciences, National Academy Press: Washington, D.C. 1998.
  • Gregor J. L. "Effect of variations in dietary protein, phosphorous, electrolytes and vitamin D on calcium and zinc metabolism." In C. E. Bodwell and J. W. Erdman, Jr., eds. Nutrient Interactions. New York, NY, Marcel Dekker, Inc; 1988.
  • Whiting S. 1994. "Safety of some calcium supplements questioned." Nutr Rev 52;95-97.
  • Smith K. T. 1987. "Calcium absorption from a new calcium delivery system (CCM)." Calcif Tissue Int. 41(6):3 51-2.
  • Compilation of research courtesy of Dr. Larry J. Milam, DHM,
    and the University of Natural Medicine, Santa Fe, NM.

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