FGF23 and chronic kidney disease: In advanced CKD (stages G4–G5), the strategy focuses on controlling CKD-Mineral and Bone Disorder (CKD-MBD), which is governed by high FGF23 acting as a barrier: High FGF23 actively suppresses the 1α-alpha-hydroxylase enzyme in the kidney, impairing the conversion of 25(OH)D to active 1,25(OH)2D.