25-hydroxyvitamin D Levels and chronic kidney disease in the AusDiab (Australian Diabetes, Obesity and Lifestyle) study

Background: Low 25-hydroxy vitamin D (25(OH) D) levels have been associated with an increased risk of albuminuria, however an association with glomerular filtration rate (GFR) is not clear. We explored the relationship between 25(OH) D levels and prevalent chronic kidney disease (CKD), albuminuria and impaired GFR, in a national, population-based cohort of Australian adults (AusDiab Study). Methods: 10,732 adults >= 25 years of age participating in the baseline survey of the AusDiab study (1999-2000) were included. The GFR was estimated using an enzymatic creatinine assay and the CKD-EPI equation, with CKD defined as eGFR <60 ml/min/1.73 m(2). Albuminuria was defined as a spot urine albumin to creatinine ratio (ACR) of >= 2.5 mg/mmol for men and >= 3.5 for women. Serum 25(OH) D levels of <50 nmol/L were considered vitamin D deficient. The associations between 25(OH) D level, albuminuria and impaired eGFR were estimated using multivariate regression models. Results: 30.7% of the study population had a 25(OH) D level <50 nmol/L (95% CI 25.6-35.8). 25(OH) D deficiency was significantly associated with an impaired eGFR in the univariate model (OR 1.52, 95% CI 1.07-2.17), but not in the multivariate model (OR 0.95, 95% CI 0.67-1.35). 25(OH) D deficiency was significantly associated with albuminuria in the univariate (OR 2.05, 95% CI 1.58-2.67) and multivariate models (OR 1.54, 95% CI 1.14-2.07). Conclusions: Vitamin D deficiency is common in this population, and 25(OH) D levels of <50 nmol/L were independently associated with albuminuria, but not with impaired eGFR. These associations warrant further exploration in prospective and interventional studies.