LAUSR

BACKGROUND Although nonhuman animal models have strongly suggested that vitamin D suppresses the renin-angiotensin system (RAS) and albuminuria, human data are largely lacking. The aim of this study was to examine the relationship between 25-hydroxyvitamin D [25-(OH)D] level and albuminuria and urinary angiotensinogen (UAGT) level in renal transplant recipients (RTRs). We also planned to investigate the effect of calcitriol treatment on albuminuria and UAGT level in these patients. METHODS AND RESULTS A total of 124 nondiabetic RTRs participated in this study. UAGT level was positively correlated with the urinary albumin-creatinine ratio (UACR) in all patients (r = 0.855; P < .001). The mean UACR (P = .036) and UAGT/urinary creatinine (UCr) level (P = .02) were significantly higher in RTRs with low 25-(OH)D than in RTRs with normal 25-(OH)D level. RTRs with low 25-(OH)D level were randomized to receive either 0.25 μg/d calcitriol (n = 40) or placebo (n = 40). All of the parameters were assessed again 12 months later in both groups. The mean UACR (P = .014) and UAGT/UCr level (P = .012) were significantly lower in the calcitriol group than in the placebo group at the end of the study. CONCLUSIONS Low 25-(OH)D status may be related to the elevation in albuminuria and UAGT, and calcitriol may have a beneficial effect on albuminuria through the inhibition of intrarenal RAS in RTRs.