The most important and most plentiful mineral in our body is calcium. It is estimated that this major mineral comprises nearly two percent of the entire body weight of an average adult. This percentage may be better noted by the average weight of calcium in pounds in both men and women. Studies suggest that adult males conserve nearly two to three pounds of calcium in their bodies, while females maintain an average of one to two pounds. 
The majority of calcium, virtually 99%, is stored in our skeletal structure and teeth. The remaining percent is stored in soft tissues, cell membranes, and bodily fluids. Many individuals supplementing calcium in their diets think of this mineral as being inert, or not having the ability to move or act in bodily processes. We consume this mineral and often times assume that calcium in just stored as a density and protection mechanism for various conditions that are related to both tooth and bone structure. This, however, is untrue. Calcium is constantly flowing into and out of bone.
When certain percentages of calcium are low, bones release stored calcium to optimize blood serum levels. The same is true for the opposite. If blood levels are too rich in calcium, bones will absorb this excess, and the remaining amounts are either absorbed in the intestinal tract or excreted via urine.
There are certain nutrients that directly coincide with our ability to absorb calcium from dietary sources. In the complexity of calcium absorption, vitamin D, parathyroid hormone, and, the amino acid lysine, provide a synergistic effect on overall calcium absorption and its associated metabolic processes within the body. Also of importance are nutrients consumed in the diet that hinder calcium absorption. Nutrients and compounds such as phosphorus, iron, oxalic acid, phytic acid, and fiber, all adversely effect the absorption of this vital mineral.
There are various forms of calcium consumed in the various dietary foods and nutritional supplements we consume to achieve our daily adequate intakes. The average adult readily absorbs approximately 30-40% of all ingested dietary calcium. Listed below are the most common forms of calcium, listed in order of their bioavailability:
- Calcium aspartate
- Calcium citrate
- Calcium carbonate
- Calcium gluconate
- Calcium lactate
- Calcium chloride
Calcium aspartate remains one of the most soluble forms of supplemental calcium. Often categorized as an amino acid, it is actually a calcium salt, formed from the binding of calcium and the amino acid aspartic acid. Aspartic acid is critical in the many delivery mechanisms of calcium to various sites within the body. The combination of a mineral and amino acid provide for far greater absorption, assimilation, and usage. Calcium aspartate has been utilized for muscle cramps, spasms, pain, insomnia, anxiety, and muscular tension. Calcium citrate and aspartate may also be beneficial for individuals concerned with the acid-based balance of their bodies.
Calcium is required for the important processes of growth, maintenance, reproduction (protein structuring of DNA and RNA), tooth and bone growth, the metabolism of lipids, and also helps to maintain the integrity of cell membranes and their permeability at any given time. It may also assist persons in the maintenance of a regular heartbeat, and be equally beneficial for proper nerve transmission and functioning. Calcium is also crucial in the development of many enzymes (e.g. lipase) which allow our body to digest nutrients needed for the maintenance of our overall health.
|Food||Measurements||Mg of Calcium|
|Molasses cane, third extraction or blackstrap||1 cup: 328g||2243|
|Cheese gruyere||1 pkg:170g||1718|
|Cheese edam||1 pkg:198g||1447|
|Sesame seeds whole, dried||1 cup:144g||1404|
|Pizza with cheese topping||1 pizza:520g||1149|
|Tofu fried, prepared w/calcium sulphate||100g||961|
|Molasses cane, second extraction or medium||1 cup:328g||951|
|Endive raw||1 head:513g||928|
|Tofu raw, firm, prepared w/calcium sulphate||½ cup:126g||860|
|Molasses cane, barbados||1 cup:328g||803|
|Cheese blue||1 cup:328g||712|
|Cake plain or cupcake||1 cake: 1109g||709|
|Potatoes au gratin, dry mix, prepared with water, whole milk and butter||5 ½ oz pkg:822g||682|
|Almond butter||1 cup:250g||675|
|Pancake and waffle mix dry||1 cup:147g||661|
|Cake devil’s food, w/eggs||1 cake:1107g||653|
|Baking powder||1 tbsp:13.5g||650|
|Seaweed agar, dried||100g||625|
|Rhubarb pie baked||1 pie:945g||605|
|Welsh rabbit||1 cup:232g||582|
|Collards chopped||10 oz pkg:284g||571|
|Tofu raw, firm, prepared w/calcium sulphate||¼ block:81g||553|
|Molasses cane, first extraction or light||1 cup:328g||541|
|Lambsquarters cooked||1 cup chopped:180g||464|
|Pumpkin pie baked||1 pie:910g||464|
|Milk shake vanilla||1 glass:313g||457|
|Yogurt plain, skim milk||1 tub:227g||452|
|Soup cream of celery, canned||1 can:602g||452|
|Tofu raw, regular, prepared w/calcium sulphate||½ cup:124g||434|
|Soup cream of mushroom, canned||1 can:602g||433|
|Cabbage raw||1 head:908g||427|
|Tostada with guacamole||2 tostadas:261g||423|
|Wheat flour white self-raising, enriched||1 cup:125g||423|
|Potatoes O’brien||1 dish: 1162g||418|
|Tofu raw, regular prepared w/calcium sulphate||¼ block:116g||406|
|Kale raw||10 oz pkg:284g||386|
|Soup tomato, canned||1 can:602g||385|
|Cheese parmesan||1 oz:28g||385|
|Almonds dried||1 cup kernels:142g||377|
|Macaroni and cheese||1 cup:200g||362|
|Carob flour||1 cup:103g||358|
|Collards cooked||1 cup chopped:170g||357|
|Rhubarb cooked||1 cup:240g||348|
|Turnip greens||10 oz pkg:284g||335|
|Eggs yolk only||1 cup:243g||333|
|Spinach frozen||10 oz pkg: 284g||315|
Average Intake of Calcium in the Typical American Diet:
The “Other Foods” category includes eggs (1.7%), fats and oils (0.1%), sugars and sweeteners (0.8%), and miscellaneous foods (2.6%). 
The clinical application for calcium supplementation in diet has been widely observed. Dietary consumption of calcium on a daily basis is needed to provide our bodies for an array of processes associated with maintenance of our current health, and for assistance in the prevention of future diseases/afflictions.
The most popular use of calcium is within its ability to provide growth and maintenance for both tooth and bone structure. Calcium not only prevents the likelihood of one developing conditions such as osteomalacia and osteoporosis, but its supplementation is also equally critical in periods of rapid growth (i.e. childhood, pregnancy).  It is important to note that the bone densities we have in the latter stages of our lives are a direct result of calcium intake during the first three decades of our lives.
Bone health has been an topic of interest in the media concerning pre and postmenopausal women. The roles of calcium have also been highlighted concerning the prevention and treatments of specific bone diseases. But many of these reports are misleading. Although calcium supplementation is beneficial and may dramatically slow the symptoms associated with certain bone-related diseases, it will not stop the onset of osteomalacia, nor osteoporosis in postmenopausal women.  It remains true, however, that women may derive greater health benefit from higher concentrations of calcium in not only conditions associated with tooth and bone structures, but also with hormonal regulation. Calcium may assist in symptoms associated with PMS (pre-menstrual syndrome), and directly aid in bone mineral density preservation of post-menopausal women. [6-8]
In relation to our tooth and gum structures, calcium supplementation combined with vitamin D may slow the rate of tooth disease and tooth loss.  It may also protect against diseases associated with the gums (gingivitis), particularly in females.
Lower concentrations of calcium in the blood have also been linked to many cardiovascular-associated problems in both men and women. High blood pressure, elevated cholesterol, and the possibilities of stroke, have all been targeted in clinical application. Studies have shown that calcium supplementation from a dietary or external source (a nutritional supplement), can improve and decrease blood pressure and blood cholesterol levels. Cholesterol levels monitored in subjects participating in research studies have shown dramatic decreases in cholesterol levels with dosages of calcium administered in ranges from 1,500 milligrams to 2,000 milligrams per day.  Research indicates that both high cholesterol and blood pressure may increase the incidence of stroke.  For this reason, many medical practitioners encourage the supplementation of calcium for all three of these acute and chronic conditions.
The effect of calcium supplementation in relation to preeclampsia is of serious interest to many researches in the medical community. This is a pregnancy-induced increase in the overall systolic blood pressure levels that can lead to complications within the third trimester of pregnancy. Calcium supplementation, usually through the form of prenatal vitamins, may offer protection against this particular complication of pregnancy. 
Calcium supplementation for cancer patients has also received much attention in the last decade. Colorectal cancer (cancer of the colon) has been thoroughly researched in combination with calcium supplementation. Studies have included calcium in union with vitamin D and milk in the diets of patients suffering from colon cancer.  Findings indicate that these nutrients may specifically reduce the risk of not only colon cancer, but also prostate and breast cancers. 
Other areas of studies in regards to the effects of calcium supplementation on the body include obesity and insomnia. Although one can not attribute the supplementation of calcium alone to improving these conditions, an improvement was seen in both afflictions during clinical research. In insomnia for instance, calcium supplementation proved more effective and readily absorbed before bed time. It has been suggested that this calcium supplementation promotes a more restful, rather than restless, sleep.
The Dietary Reference Intakes and Recommended Daily Allowances of calcium are listed below. The Recommended Dietary Allowances (RDA) for calcium are based upon serving sizes and are divided into three separate age demographics; pediatrics, adolescents, and adults.
|0-6 months||210 mg/day|
|7 months-1 year||270 mg/day|
|Ages 19-51||1,000 mg||1,000 mg|
|Under 19||1,300 mg||1,3000 mg|
|Over 19||1,000 mg||1,000 mg|
It is important to note that Adequate Intakes (AI) have been set for calcium. The Food and Nutrition Board of the National Academy of Sciences has set this intake at 1,000 milligrams per day for men and women aged 19 - 50, and 1,200 milligrams per day for individuals older than 50 years of age.
Calcium toxicities occur many times when one exceeds the amount of 2,500 milligrams per day over an extended duration. Signs and symptoms may include;
- upset stomach
- prolonged vomiting
- kidney toxicity
- irregular heartbeat/rhythm
- loss of appetite
- mental confusion
“Mega dosing” with calcium-containing supplements may enhance the risk of an individual developing either calcium kidney stones, or calcium deposits in body tissues. 
Individuals at risk for an overdose of calcium include persons with various forms of cancer, individuals with kidney ailments (i.e. dialysis or disease), and those suffering from hyperparathyroidism. Calcium supplementation is not recommended in these individuals because of the increased risks associated to various toxicity conditions.
Deficiencies of calcium are seen in specific conditions of both children and adults. In children, Rickets is of a major concern to a child’s overall skeletal health and development. Although Rickets is primarily caused by a D vitamin deficiency, recent studies have indicated that proper dietary intake of calcium in children may be as important, if not more important, than vitamin D in the prevention and formation of this childhood condition.  The deficiency that causes Rickets is rare in the Western block of the world, due to the fortification of vitamin D in milk and milk-containing products.
In adults, a prolonged deficiency of calcium will likely result in osteomalacia and/or osteoporosis. This is seen primarily in women, and it is estimated that 25% of American women do not receive adequate intake of this mineral.  The effects of osteoporosis in women are caused by either too little bone mass accumulation during the first three decades of life, or an increased rate of bone loss during menopause. Men can also suffer from this condition, but it is very uncommon.
A deficiency in calcium will also create an increased intake of lead by the teeth and various bone structures located throughout the body. This toxic metal is a substance that may lead to other complications not directly associated solely to calcium.
Possible Drug Interactions
Because of the extreme importance of calcium in our bodily processes throughout the entirety of our lives, possible drug interactions that may inhibit the absorption of calcium are listed:
- Alendronate (osteoporosis medication)
- Antacids, Aluminum-containing
- Blood pressure medications
- Cholesterol-lowering medications
- Digoxin (irregular heartbeat medication)
- Gentamicin (antibiotic)
- Metformin (medication used to treat type II diabetes)
- Quinolone antibiotics
- Seizure medications
1. Herbert, Victor. “Vitamins and Minerals Plus Antioxidant Supplements” Total Nutrition Ed. Victor Herbert, M.D., Genell J. Subak-Sharpe, M.S. New York: Saint Martin’s Griffin, 1995. 94-118.
2. Gerrior SA, Zizza C., 1994. Nutrient Content of the U.S. Food Supply, 1909 - 1990. Home Economics Research Report No. 52. U.S. Department of Agriculture, Washington, D.C
3. Abrams SA. Calcium turnover and nutrition through the life cycle. Proc Nutr Soc. May2001;60(2):283-9.
4. 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.
5. Dawson-Hughes B. Calcium supplementation and Bone Loss: A Review of Controlled Clinical Trials. Am J Clin Nutr. Jul 1991;54(1):274S-80S.
6. Thys-Jacobs S, Starkey P, Bernstein D, Tian J. Calcium carbonate and the premenstrual syndrome: effects on premenstrual and menstrual symptoms. Premenstrual Syndrome Study Group. Am J Obstet Gynecol. 1998;179:444-452.
7. Lobo RA, Roy S, Shoupe D, et al. Estrogen and progestin effects on urinary calcium and calciotropic hormones in surgically- induced postmenopausal women. Horm Metab Res. 1985;17(7):370-373.
8. Ruml LA, Sakhaee K, Peterson R, et al. The effect of calcium citrate on bone density in the early and mid-postmenopausal period: a randomized placebo-controlled study. Am J Ther. 199;6:303-311.
9. Krall EA, Wehler C, Garcia Rl, et al. Calcium and vitamin D supplements reduce tooth loss in the elderly. Am J Med. 2001 Oct 15;111(6):452-456.
10. Allender PS, Cutler JA, Follman D, Cappuccio FP, Pryer J, Elliot P. Dietary calcium and blood pressure: a meta-analysis of randomized clinical trials. Ann Intern Med. 1996;124(9):825-831.
11. Iso H, Stampfer MJ, Manson JE, et al. Prospective study of calcium, potassium, and magnesium intake and the risk of stroke in women. Stroke. 1999;30(9):1772-1779.
12. Walker JJ. Pre-eclampsia. Lancet. 2000;356(9237): 1260- 1265.
13. Kampman E, Slattery ML, Caan B, Potter JD. Calcium, vitamin D, sunshine exposure, dairy products and colon cancer risk (United States). Cancer Causes Control. 2000:11:459-466.
14. Chan JM, Stampfer MJ, Ma J, Gann PH, Gaziano JM, Giovannucci EL. Dairy products, calcium, and prostate cancer risk in the Physicians’ Health Study. Am J Clin Nutr. 2001;74(4):549- 554.
15. Standing Committee on the Scientific Evaluation of Dietary Intakes, Food and Nutrition Board, Institute of Medicine. 1997. Dietary Reference Intakes for Calcium, Phosphorus, and Magnesium, Vitamin D, and Flouride, National Academy Press, Washington D.C.
16. Thatcher TD, Fischer PR, Pettifor JM, et al. A comparison of calcium, vitamin D, or both for nutritional rickets in Nigerian children. N Engl J Med. 199;341:563-568.