RTRs with vitamin D insufficiency , defined as circulating @-hydroxyvitamin D levels of less than @ ng/ml ( or @ nmol/l ) , will be randomized between @ and @ months after transplantation to blinded groups to receive vitamin D@ ( cholecalciferol ) either at high or low dose ( respectively , @,@ UI or @,@ UI every @ weeks for @ months then monthly for @ months ) with a follow-up of @ years .