• Yun Jung Oh, Myounghee Kim, Hajeong Lee, Jung Pyo Lee, Ho Kim, Sejoong Kim, Kook-Hwan Oh, Kwon Wook Joo, Chun Soo Lim, Suhnggwon Kim, Yon Su Kim, and Dong Ki Kim.
• Department of Internal Medicine, Seoul National University Hospital, Seoul, Korea.
• Nephrol. Dial. Transplant. 2012 Jun 1;27(6):2396-403.

BackgroundVitamin D deficiency is known as an important risk factor for mortality in patients with chronic kidney disease (CKD). Nevertheless, the association of renal function itself with vitamin D status or serum 25-hydroxyvitamin D (25OHD) level has not been investigated thoroughly.MethodsWe examined the association between the estimated glomerular filtration rate (eGFR) and serum 25OHD levels using data from the 4th Korean National Health and Nutritional Examination Survey 2008. Generalized additive models (GAMs) were used to examine the relationship between eGFR and serum 25OHD levels and to estimate a threshold value of eGFR that predicts changes in serum 25OHD levels.ResultsThe mean serum 25OHD level was 20.4 ± 9.1 ng/mL, and the overall prevalence of vitamin D deficiency was 29.9% in this population. The prevalence of vitamin D deficiency began to increase at eGFR levels <45 mL/min/1.73 m(2). After adjustment, the logistic regression of dichotomized eGFR levels with a cut-point of 45 mL/min/1.73 m(2) yielded an increased odds ratio for vitamin D deficiency. Additionally, the continuous relationship between eGFR and 25OHD levels was explored using GAMs adjusted for various confounding factors. In this analysis, the difference from the mean serum 25OHD started to increase below an eGFR threshold of 55.4 mL/min/1.73 m(2), which suggests that renal function is directly related to the serum 25OHD levels in patients with CKD Stages 3-5.ConclusionAlthough moderate renal dysfunction (eGFR < 45 mL/min/1.73 m(2)) is an important predictor of vitamin D deficiency, serum 25OHD levels start to decrease below an eGFR level of ~60 mL/min/1.73 m(2) independent of other risk factors. These results suggest that more careful attention to 25OHD levels may be needed when patients reach Stage 3 CKD.

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