Calcium is the most abundant cation in the human body. It is needed for so many different functions in the body, from bones, to blood clotting, your muscles [contraction and relaxation] etc. The skeleton provides structural support for organs and muscles. People often think of bones as a static piece of the body, where very little change occurs, but that is a totally incorrect perception. Bone is a dynamic part of the body and calcium is constantly flowing into, and out of it. It also stores essential minerals such as phosphorus and magnesium.
     Teeth and bones contain about 99% of the body's calcium and are dependent upon calcium for strength and structure; the remaining 1% is circulated in blood. It activates enzymes in various metabolic pathways and aids in blood clotting. Calcium as food or dietary supplements is ingested in the form of relatively insoluble salts. The mineral is absorbed in the ionized form and must be released from these salts. Both an active and passive transport mechanisms are responsible for absorption of calcium in the small intestine. During digestion, calcium is freed from calcium complexes into a soluble form, which can be ionized for absorption.

Required For:
* Calcium is needed for the formation and maintenance [mineralization] of bones, the development of teeth and healthy gums. Bone remodeling for the formation of sturdy skeletal mass during linear bone growth.
* It is necessary for blood clotting, stabilizes many body functions and is thought to assist in bowel cancer, has a natural calming and tranquilizing effect and is necessary for maintaining a regular heartbeat and the transmission of nerve impulses [neuromuscular activity], helps with lowering cholesterol, muscular growth, the prevention of muscle cramps, and stimulation of secretory activity in endocrine, exocrine and neurocrine cells.
* Calcium provides energy, breaks down fats, maintains proper cell membrane permeability, and helps to keep the skin healthy, the regulation of contraction and relaxation in cardiac and skeletal muscle. * This mineral also stops lead from being absorbed, acts as an important intracellular messenger, and is instrumental in the regulation of various enzymes, probably through calmodulin.
* Furthermore it also helps with protein structuring in DNA and RNA.

Deficiency:
     Calcium exists in bone in the form of hydroxyapatite, which comprises approximately 40% of the weight of bone. Prolonged bone re-absorption from chronic dietary deficiency, malabsorption or other factor results in osteoporosis - from either too little bone mass accumulation during growth or higher rate of bone loss at menopause. Osteoporosis is a bone-thinning condition disease that results in reduction in mass of bone per unit of volume which can lead to small and not-so-small fractures and is increasingly being found in younger women as dairy products and meat consumption increases.
     Osteomalacia results from deficiency or loss of calcium salts due to vitamin D deficiency. It is softening of the bone in adults, usually caused by a failure of normal bone calcification. Osteopenia is reduction of bone mass due to an imbalance between bone breakdown and bone formation. Resorption rates are higher than bone formation rates, resulting in demineralization and ultimately osteoporosis. Dietary calcium deficiency also has been associated with increased risk of hypertension, and colon cancer - two things that are directly tied to the consumption of animal products.
     When it is in short supply, a variety of symptoms from aching joints, eczema, elevated blood cholesterol, heart palpitations, brittle nails, hypertension (high blood pressure) and insomnia can become evident. Muscle cramps, nervousness, numbness in the arms and legs, rheumatoid arthritis, convulsions, depression and delusions have also been noted. Deficiency can result from a low dietary intake of calcium, reduction of stomach acid, high protein intake, low vitamin D status and increased GI motility.
     Hypocalcemia is frequently asymptomatic and is often seen with underlying disorders (e.g., cataracts, basal ganglia calcification, and chronic candidiasis in some patients with idiopathic hypoparathyroidism). Clinical manifestations are primarily neurologic. Slowly developing insidious hypocalcemia may produce mild encephalopathy.
     The most characteristic syndrome of hypocalcemia is tetany, resulting from severe hypocalcemia. Tetany is characterized by sensory symptoms consisting of paresthesia of the lip, tongue, fingers and feet. Other symptoms include carpopedal spasm, generalized muscle aching, and spasm of facial musculature.
     Vitamin D deficiency may be due to inadequate intake, a decreased exposure to sunlight, hepatobiliary disease or intestinal malabsorption. It is associated with rickets in children and osteomalacia in adults. A diet lacking calcium, vitamins D, C, K, magnesium, zinc and phosphorus may all increase the risk of osteoporosis. This can cause skeletal weakness and increased bone resorption resulting in bone fractures.

     Deficiency or absence of parathyroid hormone (hypoparathyroidism), a hormone deficiency characterized by low serum calcium and high serum phosphorus concentrations, is commonly seen with chronic tetany. Other incidences of hypocalcemia, due to the result of:
   Renal tubular disease
   Mg depletion
   Renal failure
   Septic shock
   Acute pancreatitis
   Excessive secretion of calcitonin
   Idiopathic hypoparathyroidism
   Pseudohypoparathyroidism
   Hypoproteinemia

RDA:

Recommended Daily Allowance
Age	mg
Infants 0 to 6 months 7 to 12 months	210 270
Children 1 to 3 years 4 to 8 years	500* 800*
Males/Females 9 to 13 years 14+ years 19+ years 50+	1300* 1300* 1000* 1200*
Pregnancy <= 18 years 19 to 50 years	1300* 1000*
Lactation <= 18 years 19 to 50 years	1300* 1000*
The maximum safe level of calcium is 2.5grams/day.

     *There are dramatic differences between international and U.S.-based recommendations for calcium intake, which primarily reflect differences in protein consumption, since protein intake interferes with calcium absorption. For adults older than 50 years, the World Health Organization recommends an intake of 400-500 mg of calcium per day from a variety of sources.¹ For the same age group, the U.S. Institute of Medicine (IOM) recommends a calcium intake of 1,200 mg per day.² The IOMs recommendations for younger adults and children are also higher than those of health organizations in other countries.³
Animal protein (beef, poultry, fish, and egg) causes calcium to be excreted in the urine. A person following a diet that does not include animal protein may have lowered calcium needs. For example, a vegan consuming a healthy "low" protein, low sodium diet may only need as little as 500 mg of calcium daily. A person consuming a high protein, high sodium diet may need as much as 2000 mg of calcium per day.

References
[1] Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. In: Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, eds: National Academy Press; 1997.
[2] Lanou AJ, Berkow SE, Barnard ND. Calcium, dairy products, and bone health in children and young adults: a reevaluation of the evidence. Pediatrics. 2005;115(3):736-743.
[3] Cumming RG. Calcium intake and bone mass: A quantitative review of the evidence. Calcif Tissue Int. 1990;47:194-201.

Toxicity:
     Excess calcium supplementation [via pill or dairy] has been associated with some mineral imbalances such as zinc, but combined with a magnesium deficiency it may cause deposits to form in your kidneys, which could cause kidney stones.

Enhanced By:
     It is recommended to take one to two parts of calcium and phosphorus to one part of magnesium.
Vitamin D as well as vitamins A and C are beneficial to have around this nutrient and it is great when taking a supplement that it is chelated with amino acids.

When More May Be Required:
     If you suffer from osteoporosis, are lacking in Vitamin D, if you have a gum disease or eat processed foods, ingest excess protein, fat, sugar or caffeine, salt or fizzy soda drinks. Drinking bottled water with a low mineral content could require more dietary calcium and so may the consumption of alcohol, taking a birth control pill, diuretic (water pill) antacids or if you are on hormone replacement therapy.

Negatively Affected By:
     Phosphorus, sodium, alcohol, coffee and white flour aids the loss of calcium from the body, while too much low-quality protein, fat and sugars [from eggs, flesh, milk, carbonated sugar water and other junk"foods"] can have a negative effect with the absorption thereof. Tetracycline and calcium bond together which impairs the absorption of both.

Interesting Notes:
     Estrogen promotes deposits of calcium in the bones. Independent studies show that those who consume the most milk, fortified with vitamin D, have higher rates of osteoporosis than those who consume little, and vegans suffer from this condition the least.

Bioabsorption rates:

calcium lactate [dairy] = 28% and has the bonus 'nutrients' known as saturated fat and cholesterol as well as natural and artificial disease-promoting growth hormones.

calcium carbonate = 26%

tri-calcium phosphate = 32%

Calcium carbonate is more difficult to absorb on an empty stomach, it needs an acidic environment to enhance absorption [so have a piece of fruit!].

Calcium absorption levels of plant foods:

Deep green vegetables = 50-70%
(broccoli, Brussel sprouts, Chinese and green cabbage, kale, kohlrabi, etc.)

Almonds = 21%

Beans = 17%

Spinach, cooked = 5%

The percent of calcium absorbed decreases as the calcium load increases; therefore calcium carbonate absorption is greatest in doses of 500 mg or less, with food.

     Since calcium citrate is highly soluble in acid, it is better absorbed on an empty stomach. The citrate form does not need gastric acid for absorption. Calcium lactate [stolen milk if not coming from the drinkers' own mother or surrogate] can be absorbed at various pHs and does not need to be taken with food for absorption for these reasons.
     Elemental calcium refers to the amount of calcium found in a product because calcium alone is unstable. Calcium phosphate is insoluble and is believed (bad faith) to be poorly absorbed despite having a higher absorption rate than milk...
     Absorption declines with age and inadequate vitamin D intake and varies among individuals: the average absorption being more efficient in males than females. Young infants and approximately 30% of elderly have low secretion of hydrochloric acid by gastric parietal cells. It has been established that low hydrochloric acid secretion can lead to decreased absorption of some minerals. Conflicting results have been reported in clinical studies on the effects of intraluminal gastric pH values on calcium absorption.
     Calcium absorption can be decreased by high intake of foods that contain oxalic acid (spinach, chard, beet greens), phytic acid in unleavened whole grains, intake of phosphorus-containing foods (meat, eggs and dairy or soda), stress, lack of movement, diazide diuretics, laxatives or aluminum-containing medications.
NOTE: decreased does not mean blocked

Food Sources:
     Beans, nuts, molasses and fruit as well as green leafy vegetables supply good, healthful amounts of calcium. One cup or 8 oz of fruits and vegetables like broccoli, turnip greens, mustard greens, legumes and dried fruits contain anywhere from 56 to 300 mg of calcium.
Vegan Diet Promotes Atheroprotective Antibodies In Patients With Rheumatiod Arthritis

Avoid Flesh:
     Animal protein [in fish, poultry, red meat, eggs, and dairy products] tends to leach calcium from the bones and encourages its passage into the urine. Plant protein [in beans, grains, and vegetables] does not appear to have this effect.¹

Regarding Milk:
     Cows milk is the perfect nutritious food...for calves, not humans. Although many people think of calcium in the diet as good protection for their bones, this is not at all the whole story. In fact, in a 12-year Harvard study of 78,000 women, those who drank milk three times a day actually broke more bones than women who rarely drank milk.²
     Similarly, a 1994 study of elderly men and women in Sydney, Australia, showed that higher dairy product consumption was associated with increased fracture risk. Those with the highest dairy product consumption had approximately double the risk of hip fracture compared to those with the lowest consumption.³
     Although Americans consume high levels of calcium, nearly three-fourths of which is in the form of dairy products,⁴ they also sustain high rates of osteoporosis and osteoporosis-related fractures.^5,6 Osteoporosis and hip fracture rates are higher in developed countries with higher calcium intakes than in sub-Saharan Africa or Asia.^7,8

References
[1] Remer T, Manz F. Estimation of the renal net acid excretion by adults consuming diets containing variable amounts of protein. Am J Clin Nutr 1994;59:1356-61.
[2] Feskanich D, Willett WC, Stampfer MJ, Colditz GA. Milk, dietary calcium, and bone fractures in women: a 12-year prospective study. Am J Publ Health 1997;87:992-7.
[3] Cumming RG, Klineberg RJ. Case-control study of risk factors for hip fractures in the elderly. Am J Epidemiol 1994;139:493-503.
[4] United Nations. Report of a joint Food and Agriculture Organization of the United Nations/World Food Organization of the United Nations expert consultation. Human vitamin and mineral requirements [ftp://ftp.fao.org/es/esn/nutrition/vitmi.html. Accessed June 2, 2007.
[5] Abelow B, Holford T, Insogna K. Cross-cultural association between dietary animal protein and hip fracture: a hypothesis. Calcif Tissue Int. 1992;50:14-18.
[6] Cooper C, Campion G, Melton L. Hip fractures in the elderly: a world-wide projection. Osteoporos Int. 1992;2:285-289. [7] Riggs B, Melton L, III. Osteoporosis: etiology, diagnosis, and management, 2nd ed.: Lippincott-Raven; 1995.
[8] World Health Organization. WHO Technical Report Series 916: Geneva, Switzerland; 2003.