D-Hormone
The Pro-D hormone synthesized by the body itself is cholecalciferol or (formerly) vitamin D3. Under the influence of UV-B, this is produced in the skin from a cholesterol derivative which is formed in the liver. The actual active form of D3 is calcitriol, which is synthesized in the kidney. In the diet, D3 is mainly found in fatty fish or is added to foods as a dietary supplement.
It has the function of a so-called prohormone in the body and is converted to the hormone calcitriol. Due to its formation and effect, vitamin D is considered to be similar to hormones. It plays an important role in the metabolism of the minerals calcium and phosphate, so it is extremely important for bone formation. Among other things, calcitriol promotes the absorption of calcium from the intestine and, together with the parathyroid gland, controls the level of calcium in the blood. In renal insufficiency less calcitriol is produced in the kidney and a calcium deficiency (hypocalcemia) develops.
Es trägt dazu bei, die Knochen-Stammzellen zu differenzieren, hilft bei der ausgeglichenen Regulation des Kalziumauf und -abbaus und verhindert die Freisetzung von überschüssigem Kalzium aus den Knochen. Ein D-Hormon-Mangel führt mittelfristig bei Kindern zu Rachitis und bei Erwachsenen zu Osteomalazie.