Background/Aims: Vitamin D (VD) is widely recognized as renal protective. However, whether VD supplementation provides benefit to patients with diabetic nephropathy (DN) remains controversial. Here, we performed a meta-analysis to systematically evaluate the impact of VD supplementation on indexes of renal function, inflammation and glycemic control in DN patients, and to explore the potential renal protective mechanism of VD. Methods: We searched Pubmed, Embase, Cochrane Library, and three major Chinese biomedical databases (CNKI, WANGFANG and VIP) for randomized controlled trials (RCTs) examining the effects of VD or its analogs in DN patients, published between September 2007 and July 2018. Quality assessment and data extraction were performed independently by two authors, according to the Cochrane systematic review methods. Meta-analysis based on the extracted results were performed via Revman 5.2 software. Results: We included 20 RCTs representing 1,464 patients with DN in this meta-analysis. VD supplementation significantly reduced 24-hour urine protein [MD = -0.26; 95% CI (-0.34, -0.17); P < 0.00001; I2 = 95%], UAER [MD = -67.36; 95% CI (-91.96, -42.76); P < 0.00001; I2 = 97%], hs-CRP [MD = -0.69; 95% CI (-0.86,-0.53); P < 0.00001; I2 = 0%], TNF-α [MD = -56.79; 95% CI (-77.05, -36.52); P < 0.00001; I2 = 89%] and IL-6 [MD = -0.73; 95% CI(-1.03, -0.44); P < 0.00001; I2 = 0%]. However, VD supplementation failed to decrease SCr [MD = -0.83; 95% CI (-3.67,2.02); P = 0.57; I2 = 0%] or increase eGFR [MD = 2.13; 95% CI (-2.06, 6.32); P = 0.32; I2 = 0%]. In addition, VD supplementation showed no impact on indexes of glycemic control, such as HbA1c [MD = 0.01; 95% CI (-0.09, 0.11); P = 0.84; I2 = 0%] and FBG [MD = -0.05; 95% CI (-0.29, 0.20); P = 0.70; I2 = 0%]. Analysis of 24-hour urine protein, SCr, eGFR, hs-CRP or HbA1c revealed no difference between subgroups based on the type of VD supplementation, including calcitriol, alfacalcidol and vitamin D3, and the dose or duration of calcitriol usage. Conclusion: In patients with DN, VD supplementation provides beneficial effects on 24-hour urine protein and inflammation indexes, but not on SCr, eGFR or glycemic control indexes. More RCTs that comprehensively evaluate the impact of VD supplementation on indexes of renal function, inflammation and glycemic control in DN atients are required in order to reach conclusive results.
Effects of Vitamin D Supplementation on Renal Function, Inflammation and Glycemic Control in Patients with Diabetic Nephropathy: a Systematic Review and Meta-Analysis