Serum 25-Hydroxyvitamin D Deficiency and the 5-Year Incidence of CKD

Background: Low serum 25-hydroxyvitamin D (25[OH] D) levels have been associated with chronic kidney disease in cross-sectional studies. However, this association has not been studied prospectively in a large general population-based cohort. Study Design: Prospective cohort study. Setting & Participants: 6,180 adults 25 years or older participating in the baseline and 5-year follow-up phases of the Australian Diabetes, Obesity and Lifestyle (AusDiab) Study. Predictor: Serum 25(OH) D levels <15 ng/mL were considered deficient. Outcomes & Measurements: Incident chronic kidney disease was defined as being negative at baseline but positive after 5 years for (1) reduced estimated glomerular filtration rate (eGFR; <60 mL/min/1.72 m(2)) or (2) albuminuria (spot urine albumin-creatinine ratio >= 2.5 mg/mmol [>= 22.1 mg/g] for men and >= 3.5 mg/mmol [>= 30.9 mg/g] for women). Results: 623 (10.9%) participants were vitamin D deficient, 161 developed incident reduced eGFR, and 222 developed incident albuminuria. In participants with and without vitamin D deficiency, annual age-standardized incidences were 0.92% (95% CI, 0.56%-1.30%) and 0.59% (95% CI, 0.51%-0.68%), respectively, for eGFR <60 mL/min/1.72 m(2) and 1.50% (95% CI, 1.06%-1.95%) and 0.66% (95% CI, 0.56%-0.76%), respectively, for albuminuria. In multivariate regression models, vitamin D deficiency was associated significantly with the 5-year incidence of albuminuria (OR, 1.71; 95% CI, 1.12-2.61; P = 0.01), but not reduced eGFR (OR, 0.93; 95% CI, 0.53-1.66; P = 0.8). Limitations: The observational nature of the study does not account for unmeasured confounders. Only baseline 25(OH) D level was measured and therefore may not accurately reflect lifetime levels. Differences in baseline characteristics of participants who were included compared with those excluded due to missing data or follow-up may limit the applicability of results to the original AusDiab cohort. Conclusions: Our prospective cohort study shows that vitamin D deficiency is associated with a higher annual incidence of albuminuria and reduced eGFR and independently predicts the 5-year incidence of albuminuria. These associations warrant further exploration in long-term prospective clinical trials. Am J Kidney Dis. 62(1):58-66. (C) 2013 by the National Kidney Foundation, Inc.