Calcium

3.4 percent of the earth's crust contains calcium, making it one of the most abundant elements. In nature, it is in the form of insoluble or poorly soluble salts. The most common are: limestone (calcium carbonate), dolomite (double calcium and magnesium carbonate) and gypsum (calcium sulphate).

Calcium was discovered in 1808 by Sir Humphrey Davy, the name comes from the Latin word calcis, which means lime.

Calcium is a silvery white, shiny, soft metal. It belongs to the group of alkaline earth metals. It is bivalent in compounds.

Natural sources of calcium

Generally, about 800 mg of calcium is ingested daily through diet. Natural sources are milk, yogurt, cheese, kelp, oats, broccoli, almonds, spinach, soy, walnuts, prunes.

Fate in the organism

Calcium ions are absorbed in the small intestine by active transport and passive diffusion. Only one-third to one-fifth of the calcium ingested with food is absorbed. Absorption depends on a number of factors. It is increased by amino acids, triglycerides, lactose, acidic medium, reduced by phytates, caffeine, alcohol, alkaline medium, fiber, phosphates, oxalates.10 - 20 percent of calcium is excreted in the urine, 80 percent in the feces amounts of endogenous calcium), while 97 to 99 percent of it is reabsorbed. Renal tubular reabsorption of filtered calcium is under hormonal control (mostly parathyroid hormone). The loss through the skin is minimal, but it increases with sweating. Excretion through hair, nails and breast milk is also minimal. The most important factors of strict control of calcium concentration are vitamin D, parathyroid hormone and calcitonin. Parathyroid hormone affects the release of calcium from the bones, increases intestinal absorption and increases renal reabsorption and increases phosphate excretion. Calcitonin reduces bone reabsorption and increases urinary excretion. Vitamin D (its active form 1,15-cholecalciferol) increases intestinal absorption of both calcium and phosphates and reduces their excretion in the urine.

Physiological role and pharmacological effect

Calcium is the most abundant mineral in the human body. The total amount of calcium in the body of an adult is 900 to 1200 g, of which 99 percent is in the bones. Small amounts of this mineral are in the extracellular fluid, it is also found in the structure of the cytoplasm and soft tissues. Approximately 50 percent of plasma calcium is in ionic form, 10 percent is in nonionic form, and 40 percent is bound to albumin. Intracellular concentration of ionized calcium is strictly regulated by ion exchange between cell and environment. Calcium is involved in many vital processes in the human body, is essential for bone ossification, is required for normal contractility of transverse striated and smooth muscles, participates in regulating cell membrane permeability, accelerates blood clotting, has a strong effect on central nervous system and excretory secretion. in synapses.

Lack

Calcium deficiency is relatively common and increased intake in some periods of life is extremely important, especially during growth and old age. Low, low calcium intake, along with some other factors, can lead to negative calcium balance and accelerated bone loss, which is common in postmenopausal women. It is the cause of osteoporosis, one of the most common diseases in old age (it occurs 6- to 8 times more often in women). This disease affects more than 200 million people worldwide (more common in whites and yellows, less common in blacks). Bones become brittle, fractures are common (especially vertebrae, femurs and joints).

Hypocalcaemia

Hypocalcaemia occurs when extracellular calcium levels are below 1.5 pmol / L. The causes are usually insufficient calcium intake with food, reduced absorption, impaired bone mineralization or lack of vitamin D and its metabolites. Parathyroid dysfunction and acute pancreatitis can also be the cause. Symptoms include paresthesias, tetany, laryngospasm, muscle spasm, grand mal, irritability, depression, psychosis, prolonged QT interval, mal absorption, and intestinal cramps.

Toxicity

Excess calcium intake may lead to hypercalcaemia, hypercalciuria and renal impairment.

Hypercalcaemia

Hypercalcaemia is a condition of increased concentration of calcium ions in extracellular fluid (greater than 2.7 pmol / L). The most common cause is increased total absorption from the gut or excessive dissolution of bone minerals. Hypercalcaemia causes depression of the nervous system, spasm of smooth muscle, especially blood vessels and intestines, and heart muscle. As a result, due to spasm of the smooth muscles of the digestive system, anorexia, constipation, nausea, vomiting. Excess calcium is deposited in soft tissues in the form of calcium phosphate.

Interactions

Calcium is one of the most commonly used food supplements, so the possibility of interactions with drugs and food ingredients is common. The timing of taking oral calcium supplements is extremely important. People over the age of 65 are recommended to take it immediately after a meal due to reduced gastric acid secretion, and younger people one to one to two hours after a meal to avoid the possibility of reduced absorption due to certain food ingredients (phytates, fiber, oxalates, fats) or increased intake of tobacco, alcohol, coffee (more than 8 cups a day). Prolonged use of calcium supplements with increased intake of dairy products can cause lactic acid syndrome.

Calcium channel blockers
Concomitant use of calcium channel blockers and calcium can significantly reduce the effectiveness of these medicines.

Thiazide diuretics
Thiazide diuretics affect the mechanism of calcium excretion and may cause hypercalcaemia due to significantly reduced excretion.

Tetracycline antibiotics
Calcium forms complexes with these drugs, thus reducing their therapeutic concentration and consequent effectiveness, so it is recommended to take at intervals of 2 to 3 hours.

Estrogen hormones
Estrogen hormones (in hormone replacement therapy or contraceptives) increase calcium absorption.

Vitamin A
Concomitant use of higher doses of vitamin A (25000 IU / day) and calcium supplements is contraindicated because vitamin A stimulates bone loss from bone and can thus cause hypercalcemia.

Vitamin D
Concomitant use of vitamin D and calcium, especially active forms, significantly increases calcium absorption and can cause hypercalcaemia. Monitoring of serum calcium levels is recommended for long-term use. Iron
Concomitant use should be avoided as reduced iron absorption occurs. It is recommended to take it every 2 to 3 hours.