Association of 1,25-Dihydroxyvitamin D Levels With Physical Performance and Thigh Muscle Cross-sectional Area in Chronic Kidney Disease Stage 3 and 4

Background: Declines in 1,25-dihydroxyvitamin D (1,25(OH)(2)D) levels and physical functioning follow the course of chronic kidney disease (CKD). Although the molecular actions of vitamin D in skeletal muscle are well known, and muscle weakness and atrophy are observed in vitamin D-deficient states, there is little information regarding vitamin D and muscle function and size in CKD. Objective: To examine associations of vitamin D with physical performance (PF) and muscle size. Design: Cross-sectional. Setting: CKD clinic. Subjects: Twenty-six patients (61 +/- 13 years, 92% men) with CKD stage 3 or 4. Main Outcome Measures: Gait speed, 6-minute walk, sit-to-stand time, 1-legged balance, and thigh muscle cross-sectional area (MCSA), measured by magnetic resonance imaging (MRI). Results: Overall, 73% were 25-hydroxyvitamin D(25(OH)D) deficient (n = 10) or insufficient (n = 9) (Kidney Disease Outcomes Quality Initiative guidelines). 25(OH)D level was associated with normal gait speed only (r = 0.41, P = .04). Normal and fast gait speed, the distance walked in 6 minutes, and sit-to-stand time were best explained by 1,25(OH)(2)D and body mass index (P < .05 for all) and 1-legged stand by 1,25(OH)(2)D (r = 0.40, P < .05) only. There were no associations of age, estimated glomerular filtration rate (eGFR), intact parathyroid hormone (iPTH), or albumin with any PF measures. MCSA was associated with eGFR (r = 0.54, P < .01) only. Variance in MCSA was best explained by a model containing 1,25(OH)(2)D, plasma Ca2+, and daily physical activity (by accelerometry) (P < .05 for all). Once these variables were in the model, there was no contribution of eGFR. Conclusion: These results suggest that 1,25(OH)(2)D is a determinant of PF and muscle size in patients with stage 3 and 4 CKD. (C) 2012 by the National Kidney Foundation, Inc. All rights reserved.