What is the optimal level of vitamin D in non-dialysis chronic kidney disease population?

AIM To evaluate thresholds for serum 25(OH)D concentrations in relation to death, kidney progression and hospitalization in non-dialysis chronic kidney disease(CKD) population.METHODS Four hundred and seventy non-dialysis 3-5 stage CKD patients participating in OSERCE-2 study, a prospective, multicenter, cohort study, were prospectively evaluated and categorized into 3 groups according to 25(OH)D levels at enrollment(less than 20 ng/mL, between 20 and 29 ng/mL, and at or above 30 ng/mL), considering 25(OH)D between 20 and 29 ng/mL as reference group. Association between 25(OH)D levels and death(primary outcome), and time to first hospitalization and renal progression(secondary outcomes) over a 3-year followup, were assessed by Kaplan-Meier survival curves and Cox-proportional hazard models. To identify 25(OH)D levels at highest risk for outcomes, receiver operating characteristic(ROC) curves were performed.RESULTS Over 29 ± 12 mo of follow-up, 46(10%) patients dead, 156(33%) showed kidney progression, and 126(27%) were hospitalized. After multivariate adjustment, 25(OH)D < 20 ng/mL was an independent predictor of all-cause mortality(HR = 2.33; 95%CI: 1.10-4.91; P = 0.027) and kidney progression(HR = 2.46; 95%CI: 1.63-3.71; P < 0.001), whereas the group with 25(OH)D at or above 30 ng/mL did not have a different hazard for outcomes from the reference group. Hospitalization outcomes were predicted by 25(OH) levels(HR = 0.98; 95%CI: 0.96-1.00; P = 0.027) in the unadjusted Cox proportional hazards model, but not after multivariate adjusting. ROC curves identified 25(OH)D levels at highest risk for death, kidney progression, and hospitalization, at 17.4 ng/mL [area under the curve(AUC) = 0.60; 95%CI: 0.685-0.69; P = 0.027], 18.6 ng/mL(AUC = 0.65; 95%CI: 0.60-0.71; P < 0.001), and 19.0 ng/m L(AUC = 0.56; 95%CI: 0.50-0.62; P = 0.048), respectively.CONCLUSION25(OH)D < 20 ng/mL was an independent predictor of death and progression in patients with stage 3-5 CKD, with no additional benefits when patients reached the levels at or above 30 ng/m L suggested as optimal by CKD guidelines.