Effect of Vitamin D Supplementation on Kidney Function in Adults with Prediabetes: A Secondary Analysis of a Randomized Trial

Background And Objectives: Low serum 25-hydroxyvitamin D (25[OH]D) concentration has been associated with higher levels of proteinuria and lower levels of eGFR in observational studies. In the Vitamin D and Type 2 Diabetes (D2d) study, we investigated the effect of vitamin D supplementation on kidney outcomes in a population with prediabetes.

Design, Setting, Participants, & Measurements: Overweight/obese adults with high risk for type 2 diabetes (defined by meeting two of three glycemic criteria for prediabetes) were randomized to vitamin D 4000 IU per day versus placebo. Median duration of treatment was 2.9 years (interquartile range 2.0-3.5 years). Kidney outcomes included () worsening in Kidney Disease: Improving Global Outcomes (KDIGO ) risk score (low, moderate, high, very high) on two consecutive follow-up visits after the baseline visit and () mean changes in eGFR and urine albumin-to-creatinine ratio (UACR).

Results: Among 2166 participants (mean age 60 years, body mass index 32 kg/m, serum 25(OH)D 28 ng/ml, eGFR 87 ml/min per 1.73 m, UACR 11 mg/g, 79% with hypertension), 10% had moderate, high, or very high KDIGO risk score. Over a median follow-up of 2.9 years, there were 28 cases of KDIGO worsening in the vitamin D group and 30 in the placebo group (hazard ratio, 0.89; 95% confidence interval [95% CI], 0.52 to 1.52]). Mean difference in eGFR from baseline was -1.0 ml/min per 1.73 m (95% CI, -1.3 to -0.7) in the vitamin D group and -0.1 ml/min per 1.73 m (95% CI, -0.4 to 0.2) in the placebo group; between-group difference was -1.0 ml/min per 1.73 m (95% CI, -1.4 to -0.6). Mean difference in UACR was 2.7 mg/g (95% CI, 1.2 to 4.3) in the vitamin D group and 2.0 (95% CI, 0.5 to 3.6) in the placebo group; between-group difference was 0.7 mg/g (95% CI, -1.5 to 2.9).

Conclusions: Among persons with prediabetes, who were not preselected on the basis of serum 25(OH)D concentration, vitamin D supplementation did not affect progression of KDIGO risk scores and did not have a meaningful effect on change in UACR or eGFR.