**4. Vitamin D deficiency: clinical implications in renal disease**

The major mechanisms for abnormal VD metabolism and VD deficiency were outlined in the section above. Of particular importance is hyperphosphatemia, caused by initial renal damage, leading to higher FGF-23 levels, which in turn suppresses CYP27B1 activity and increases 1,25VD catabolism. Suboptimal VD levels are the basis of the abnormal calcium-phosphate metabolism in renal disease. Currently, the term CKD-associated mineral bone disorder (CKD-MBD) is used to define the wide spectrum of CKD-related abnormalities in calcium-phosphate metabolism, as their importance spans beyond bone health.
