Vitamin D total (D2 + D3)
Vitamin D is a fat-soluble substance - D2 (ergocalciferol) and D3 (cholecalciferol), 1.25 (OH) 2D3 (1,25-dihydroxyvitamin D3, calcitriol). 1,25 (OH) 2D3 (1,25 - dihydroxy vitamin D3, Calcitriol) is produced from cholecalciferol or ergocalciferol. Vitamin D3 is provided by food and can be formed as a result of endogenous synthesis in the skin caused by ultraviolet radiation, while vitamin D2 is provided only through food.
Cholecalciferol precursors - previtamin D3 - are synthesized in the epidermis of previtamin D3 by ultraviolet radiation. Previtamin D3 is converted to cholecalciferol by thermal isomerization. In the epidermis, Colecalciferol Vitamin D - binds to the binding protein and in this form, it is located in the blood and transported to the liver.
Vitamin D-binding proteins also transport other cholecalciferol and ergocalciferol derivatives, including 1,25 (OH) 2D3. Cholecalciferol is found in many foods, especially fish oils, mammals, poultry, fish, and egg yolks.
Ergocalciferol is formed in plant cells by ergosterol. The main source of ergocalciferol - is 1,25 (OH) 2D3 (1,25 - dihydroxy vitamin D3, calcitriol), bread, and milk. Ergocalciferol is digested in the intestine and transported with the binding protein of vitamin D to the liver.
For diagnostic purposes, the total content of cholecalciferol and ergocalciferol and their derivatives in serum is usually determined.
D2 and D3 are hormonally inactive.
In melene, cholecalciferol and ergocalciferol are transformed into 25 (OH) D3 (25-hydroxyvitamin D3, calcidiol) by 25-hydroxylation. 25 (OH) D3? is the major circulating metabolites of cholecalciferol and ergocalciferol. Therefore, a concentration of 25 (OH) D3 can be judged on the body content of all forms of vitamin D. When testing is necessary it should be taken into account that the maximum vitamin level is in summer and the minimum is in winter. The hormonal activity of 25 (OH) D3 is 10-100 times lower than the activity of 1.25 (OH) 2D3. 25 (OH) D3 is formed in the liver in combination with the binding protein of vitamin D in the blood where it is then transported to the kidneys. Cells of the proximal renal tubule 25 (OH) D3 undergo hydroxylation at position 1- or position 24. The result is an active hormonal form of vitamin D - 1.25 (OH) 2D3 (calcitriol) or an inactive hormonal form - 24, 25 (OH) 2D3.
Both of these reactions are catalyzed by a mitochondrial enzyme 1-alpha-hydroxylase.
The rate of formation of 1,25 (OH) 2D3 depends on the amount and composition of food and the concentration of serum calcium, phosphorus, PTH, calcitonin, estrogen, growth hormone, and insulin. PTH directly stimulates the synthesis of 1,25 (OH) 2D3, activating 1 alpha-hydroxylase. Changes in calcium and phosphorus concentrations affect PTH-mediated synthesis of 1,25 (OH) 2D3: hypocalcemia decreases and hypophosphatemic PTH secretion is increased, hypercalcemia and hyperphosphatemia are suppressed.
Like PTH, 1,25 (OH) 2D3 regulates bone restructuring, stimulating intestinal calcium absorption. Due to the effect of 1,25 (OH) 2D3, the concentration of calcium ions in the extracellular fluid is maintained at the level required for the mineralization of the organic bone matrix.
Vitamin D receptors are found not only in the small intestine and bones but also in the kidneys, pancreas, skeletal muscle, smooth muscle cells of the brain, breast, colon, gonad, endothelium, cardiac myocytes, lymphocytes, monocytes.
The main role of vitamin D in the body is related to the regulation of calcium metabolism. Vitamin D levels can vary, depending on age (older people are more likely to see a drop in vitamin D levels), by season (high in summer, lower in winter), nature of food you eat, population ethnic and geographical, decrease in the level of vitamin D in the blood during pregnancy. Perve? The well-known role of vitamin D in calcium metabolism, recent studies show that a sufficient amount of vitamin D is associated with the risk of reducing various cancers, diabetes, multiple sclerosis, cardiovascular disease, tuberculosis. Vitamin D is involved in the regulation and differentiation of immune system cells, directly and indirectly