The Importance of Vitamin D in the Body
Vitamin and its metabolites
By vitamin D is meant a whole group of substances soluble in fats (D1, D2, D3, D4). Some of them, for example, D2 (ergokadtsiferol) and D3 (cholecalciferol), were known 80 years ago. These substances were discovered by the German biochemist Professor A. Windaus, who spent a long time studying sterols and proved that they are the precursors of vitamin D.
The main effects of this substance are divided into two groups: classical and nonclassical (or pleiotropic). They are carried out by metabolites of vitamin D, which are biologically active substances. The active form of the metabolite 25 (OH) D, which is formed only when the substances 25 (OH) D2 and 25 (OH) D3 is present in the body, correspond directly to the receptors of the nuclei. These forms are formed by a primary synthesis in the hepatic cells, then enter the intestine. Subsequently, in the renal tubules under the influence of many enzymes they undergo several complex metabolic reactions (an important role is recognized here for 1-alpha-hydroxylase). And all these transformations end with the formation of vitamin D – the hormone, which is responsible for the connection with the nuclear receptors.
Recently, the concepts and ideas about the vitamin in the body and its metabolism have changed significantly. The numerous discoveries made in recent years have allowed us to look at this substance in a new way. From the current point of view, this vitamin is a steroid hormone, in the synthesis of which many substances that exhibit biological activity (proteins, cholesterol, etc.) participate.