Alternatively, it could also suggest the presence of pathways that convert 25(OH)D3 to 1,24,25(OH)3D3 independently of a 1,25(OH)2D3 intermediary as suggested by Martineau et al.16 In a study of participants with moderate to severe CKD, cholecalciferol supplementation increased levels of 25(OH)D3 substantially, but the change in 24,25(OH)2D3 was more than proportional to the increase in 25(OH)D suggesting that supplementation increased delivery of 25(OH)D to CYP24A1 and/or increased CYP24A1 activity21. Here, CYP24A1 is linked to chronic kidney disease.