Impact of vitamin D on proteinuria, insulin resistance, and cardiovascular parameters in kidney transplant recipients

Abstract

Low vitamin D levels prevalent in patients with chronic kidney disease have been reported to be associated with proteinuria, insulin resistance, and cardiovascular disease. Kidney transplant recipients are also susceptible to low vitamin D levels but their clinical significance is uncertain. This study investigated the prevalence and association of vitamin D insufficiency with proteinuria, insulin resistance, and cardiovascular parameters among 95 living donor kidney transplant recipients. Levels of 25-hydroxyvitamin D [25(OH)D] were stratified into an insufficient group [25(OH)D≤30 ng/mL; n=19] versus a normal group [25(OH)D>30 ng/mL; n=76]. Proteinuria (urinary protein-creatinine [P/C]≥0.2 mg/mg), insulin resistance (homeostasis model assessment of insulin resistance [HOMA-IR]) and cardiovascular parameters were compared between groups. Twenty percent of subjects showed vitamin D insufficiency. Proteinuria was higher among the vitamin D insufficient than the normal group (47.4% vs 18.7%; P=.02). 25(OH)D levels inversely correlated with urinary P/C ratio and intact parathyroid hormone (I-PTH) levels (r=-.24, P=.02 and r=-.23, P=.02, respectively). No correlations were observed between 25(OH)D levels and HOMA-IR scores or cardiovascular parameters. On univariate analysis, proteinuria and i-PTH levels were independent predictors of vitamin D insufficiency (P<.01 and P=.03, respectively). Multivariate analysis demonstrated proteinuria to be a significant predictor of vitamin D insufficiency (odds ratio=4.526; P=.03). In conclusion, vitamin D insufficiency was common and significantly associated with proteinuria among kidney transplant recipients. Additional studies are needed to clarify the causal relationship of vitamin D insufficiency with proteinuria and to determine the role of vitamin D supplementation to attenuate the development of proteinuria.