[New findings on the metabolism and importance of the D vitamins, with special reference to the use of vitamin D].

Animal-experimental examinations show that the peroral or intramuscular application of a high dose of vitamin D2 or of D3 leads to a toxic effect of these compounds on the osteocytes and that the hypercalcaemia evoked by this is mainly to be traced back to an increased deliberation of calcium from the bones. After application of a larger dose of vitamin D the activation mechanism in the liver and in the kidneys is much inhibited for several weeks so that no formation of 1,25-hydroxy-vitamin-D takes place; consequently, no furthering effect on the mineralisation of the bones is performed. Therefore, it is recommended to use physiological doses in the prevention of rachitis (500-1,000 IU a day). During the pregnancy the activity of the enzymes which participate in the activation of the D-vitamins increases in the liver and the kidneys. The kidneys of the fetuses are able to form 1,25-hydroxy-vitamin-D. Vitamin D and 25-hydroxy-vitamin-D transgress through the placenta into the fetuses. Due to the adaptation mentioned and the increased formation of 1,25-hydroxy-vitamin-D the absorption of calcium and phosphate increases during pregnancy. Recent pathobiochemical knowledge concerning the metabolism of the D-vitamins in several diseases are described.