As the impact of Vitamin D supplementation on arterial vasomotor and stiffness function, endothelial and bone biomarkers has not been investigated systematically, this study tested the effect of treatment with oral cholecalciferol on endothelial function, arterial stiffness, biomarkers of endothelial cell activation and serum FGF-23, in relatively healthy non-diabetic CKD stage 3 and 4 patients with low levels of vitamin D. The gene discussed is FGF23; the disease is chronic kidney disease.