FGF23 and chronic kidney disease: In addition, deficiency of klotho—more commonly observed in chronic kidney disease (CKD) but also present in AKI—contributes to vitamin D insufficiency through two mechanisms: (1) by exacerbating AKI due to the loss of its inherent renoprotective functions, and (2) by promoting FGF-23–mediated suppression of vitamin D activation [48].