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Calcium (Ca) is one of the most important macroelement that is essential for maintaining homeostasis in the body. It is very important in strengthening and rebuilding bones. 99% occurs in the body in the form of hydroxyapatite and builds bone tissue. The remaining 1% of calcium resources is located in intra- and extracellular fluid, where plays an important role in many physiological processes, such as muscle contraction, release of hormones, blood clotting or nerve conduction. Moreover, calcium has anti-allergic, anti-inflammatory and antioedematous properties.

Calcium in blood serum may occur in the ionized form (approx. 50%), as phosphate, citrate, carbonate, suphate or lactate (about 10%) complexes, as well as calcium bounded to the proteins, mainly to the albumins (approx. 40%). Calcium in the ionized form is responsible for many physiological processes.

Total amount of calcium in the body is 1,4 – 1,6% of body weight, that means about 1,0 – 1,2 kg. The correct concentration of calcium in blood serum can vary between 8,8 – 10,4 mg/dl (2,20 – 2,60 mmol/l).

Recommended calcium intake is:

  • for children, youths, women and people over 50 years old: 1 200 – 1 300 mg/day,
  • for the rest of the adults: 900 – 1 000 mg/day.

The main factors affecting calcium concentration in blood serum are:

  • the amount of calcium in food,
  • degree of absorption from the digestive tract,
  • degree of excretion in the urine.

A condition in which there is the decrease of the concentration of total calcium in blood serum to value under 2,25 mmol/l and/or reduced concentration of ionized calcium to below 0,95 mmol/l is called hipocalcemia. A slight reduction in the calcium concentration below correct ones, does not give ant symptoms. Clinical signs of a significant recuction in the concentration of calcium in the blood affects most common, the neuromuscular system (tingling, numbness, status epilepticus), and the most distinctive symptom of deficiency of calcium are explicit of latent tetany.

Hypercalcemia is a condition in which the increased concentration of total calcium in the blood serum is above 2,60 mmol/l and/or ionized calcium above 1,25 mmol/l.  The cause of hypecalcemia may be: cancer, endocrine system and granulomatous diseases, medications, overdosing of vitamin D and A, as well as overdosing of calcium intake. Symptoms of hypercalcemia are not always characteristic and can affect many systems and organs: kidneys, digestive tract, cardiovascular (blood overpressure, left ventricular hypertrophy, vulvular calcification) or nervous system.

Factors that can lead to calcium deficiency are:

  • diet deficient in calcium,
  • diet rich in substances which reduces the absorption of calcium (oxalates, Mg, Zn, Cu, Sn, Na, K ions, phosphates, tetracyclines),
  • diet deficient in substances that increase the absorption of calcium (vitamin D, lactose, proteins),
  • inadequate calcium absorption from gastrointestinal tract (digestive disorders, malabsorption, shortage of active metabolites of vitamin D, hyperthyroidism of parathyroid glands),
  • inadequate release of calcium from bones,
  • excessive loss in the urine,
  • excessive deposition of calcium in the bones or soft tissues.

Bioavailability of calcium

Calcium occurs in almost all food products but the quantity and bioavailability are different. In physiological conditions it is absorbed both in duodenum and small intestine. Calcium from diet is absorbed up to 40%  and the degree of absorption is regulated by many factors such as: age, pregnancy, level of calcium in the body, concentration of vitamin D and the amount of vegetable substances in diet.

Factors affecting the increase of calcium absorption are: vitamin D, some of the proteins, bile acids, the presence of lactose (sugar contained in milk), acidic environment of intestinal.

In turn, factors that reduce calcium absorption are: oxalates (available in e.g. sorrel or beetroot leaves), zinc, copper, tin, potassium and sodium ions, phosphates, an increase on the pH of the food content, an excess of saturated fats in the diet, tetracycline.

Also the consumption of strong coffee, strong tea, large quantities of salt, smoking, consuming excessive quantities of alcohol and the use of sedatives, contraceptives, antibiotics and anticonvulsants may affect calcium metabolism disorder.

In dietary supplements containing calcium compounds, it occurs most commonly in the forms of calcium salts, such as calcium citrate, calcium malate, calcium lactate, calcium lactobionate, calcium gluconate, calcium lactogluconate, calcium gluconolactobionian, calcium carbonate and calcium phosphate. Calcium is obtained from natural sources (oyster shells, egg shells, dolomite). Inorganic calcium chelates have poor absorption. The best absorbed are organic calcium chelates (citrates, lactates, gluconates). The majority of dietary supplements containing calcium should be taken with a meal, although calcium citrate and calcium malate can be consumed regardless of the meals.

The percentage of absorbed calcium is inversely proportional to the dose of taken calcium. The efficiency of absorption of calcium from supplements is higher when the intake is in doses of 500 mg or less.

The beneficial effects of calcium:

  • protection against the development of osteoporosis– there are a lot of reports, confirming that calcium supplementation decreases the risk of osteoporosis as consequences of postmenopausal loss of bone mass, as well as prevents the development of secondary osteoporosis in patiens with asthma and rheumatoid arthritis treated with glucocosricoids.
  • large number of studies indicates a beneficial effect of the diet rich in calcium for the weight reduction and in particular reduction of the fat content. the influence of calcium on weight reduction is mainly affecting the inhibition of lipogenesis, escalation of lipolysis and absorption reduction of fatty acids in the intestine as a result of the creation of insoluble salt. however, there is a greater severity of the action of calcium from diary products that from supplements.
  • impact on lowering blood pressure– a beneficial effect of calcium is observed especially in people that are sensitive to sodium.

The powder from the eggshells is a rich source of natural calcium of high bioavailability. Eggshell is formed in chicken in the biomineralization process, 95% of its composition are inorganic compounds (mainly calcium carbonate) and about 5% of organic compounds (proteins- about 1%, lipids, lipoproteins- about 2-4%). The responsible factor for the characteristic color of the shells is pigment- biliverdin.

Natural sources of calcium tend to be particularly interesting, because of the content of other valuable for human health elements, which can have a positive effect on metabolism. Eggshells in addition to calcium, provides a large amount of significant for organism microelemnts, such as selenium, zinc, copper and strontium.

In comparison with calcium carbonate obtained synthetically, eggshells features similar calcium content, but they contain more selenium, strontium but less fluorine. However, in the preparations of the shells of crustaceans t can be observed that the content of magnesium, iron, fluorine and strontium is higher but content of calcium is worse that in eggshells.

In the eggshells it can be observed the smallest percentage of heavy metals, such as: chromium, lead, aluminum, vanadium and cadmium. This is probably due to the fact that the main task of eggshells is to protect developing embryos from harmful factors in the external environment and providing him adequate conditions for development. Heavy metals are extremely dangerous for organism development (mainly for the nervous system), therefore, they are not embedded in the shell even if they are present in the environment or feed to ensure the protection of the developing embryo.

Among the elements present in the eggshell, noteworthy is strontium, which is used for many years in the treatment of osteoporosis. The actions of strontium are to stimulate activities of osteoblasts (ossific cells) and inhibiting osteoclasts (osteoclastic cells). Strontium content in the eggshell is large enough to show beneficial affect on bone structure, however too small to cause any side effects.

In addition to these organic compounds in the eggshells, there are also the polypeptides and carbohydrates, which also have and important role in the calcium management of the body and its absorption in the intestine. All of these factors are crucial in the prevention and treatment of osteoporosis. In addition, studies have shown that undershell membrane, which is a component of eggshell powder, has influence on reducing the stiffness of the knee. What’s more, because of the presence of lysozyme it has antibacterial properties.

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