25 (OH) vitamin D levels and renal disease progression in patients with type 2 diabetic nephropathy and blockade of the renin-angiotensin system.

BACKGROUND AND OBJECTIVES: Experimental studies show that 25 (OH) vitamin D is a suppressor of renin biosynthesis and that vitamin D deficiency has been associated with CKD progression. Patients with type II diabetes and CKD have an exceptionally high rate of severe 25 (OH) vitamin D deficiency; however, it is not known whether this deficiency is a risk factor for progression of diabetic nephropathy. This study aimed to investigate whether there is an association of 25 (OH) vitamin D deficiency with disease progression in type II diabetic nephropathy.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: 25 (OH) vitamin D levels were measured at baseline and 4 and 12 months in 103 patients included in a multicenter randomized controlled trial to compare the efficacy of combining an angiotensin-converting enzyme inhibitor and an angiotensin receptor blocker with the efficacy of each drug in monotherapy to slow progression of established diabetic nephropathy during 2006-2011. The primary composite endpoint was a >50% increase in baseline serum creatinine, ESRD, or death. All study participants were included in the analysis.

RESULTS: Fifty-three patients (51.5%) had 25 (OH) vitamin D deficiency (<15 ng/ml). After a median follow-up of 32 months, the endpoint was reached by 23 patients with deficiency (43.4%) and 8 patients without (16%). Multivariate Cox regression analysis adjusted for urinary protein/creatinine ratio, estimated GFR, and baseline aldosterone showed that 25 (OH) vitamin D deficiency was associated with the primary endpoint (hazard ratio, 2.88; 95% confidence interval, 1.84 to 7.67; P=0.04).

CONCLUSIONS: These results show that 25 (OH) vitamin D deficiency is independently associated with a higher risk of the composite outcome in patients with type II diabetic nephropathy.