[Frontiers in vitamin D; basic research and clinical application. Vitamin D and secondary hyperparathyroidism]

In chronic kidney disease (CKD) , phosphate retention and low 1, 25-dihydroxyvitamin D [1, 25 (OH) ₂D] due to a decrease in the number of functioning nephrons had long been considered to contribute to the pathogenesis of secondary hyperparathyroidism (SHPT) . The discovery of fibroblast growth factor 23 (FGF23) drastically changed our understanding and provided new implication of the development of SHPT. In addition, CKD impairs the maintenance of normal 25-hydoxyvitamin D [25 (OH) D] levels which can act directly on the parathyroid glands to repress PTH synthesis. Active vitamin D therapy is widely used for the treatment of SHPT. However, the active form of vitamin D, 1, 25 (OH) ₂D and its analogs increase the calcium and phosphate levels by increasing the intestinal calcium and phosphate absorption. To suppress PTH secretion without these potential complications, several vitamin D analogs including paricalcitol, maxacalcitol and doxercalciferol are already in clinical use. A novel therapeutic concept in new vitamin D therapies are expected to improve patient outcome.