CYP27B1 and Renal insufficiency: Taken together, the currently available evidence suggests that in patients with CKD, nutritional vitamin D formulations (ergocalciferol, cholecalciferol, and calcifediol) are less effective in PTH suppression and management of SHPT compared to activated compounds, and this might mainly be due to the reduced activity of 1-α hydroxylase (CYP27B1) related to renal failure.