Although excessive vitamin C is clearly dangerous for CKD patients, there is debate as to current recommendations, especially with regard to the potential role of vitamin C in anemia management. The National Kidney Foundation Kidney Disease Outcomes Quality Initiative Clinical Practice Guidelines and Clinical Practice Recommendations for Anemia in Chronic Kidney Disease (Am J Kidney Dis. 2006;47[5 Suppl 3]:S11-S145) notes that, “in the opinion of the Work Group, there is insufficient evidence to recommend the use of vitamin C (ascorbate) in the management of anemia in patients with CKD.” However, studies examining ascorbic acid supplementation in dialysis patients hope to demonstrate the benefit of its use, particularly for patients with erythropoietin (EPO)-resistant anemia.
A study led by Attallah of EPO-hyporesponsive anemia in 42 MHD patients who also had high serum ferritin of unknown etiology, utilized IV ascorbic acid 300 mg administered thrice weekly for six months along with standard anemia management care (Am J Kidney Dis. 2006;47:644-654).
Results for the patients in the intervention group demonstrated that “vitamin C improved responsiveness to EPO, either by augmenting iron mobilization from its tissue stores or through antioxidant effects.” Although the IV ascorbic acid provided in this study was reported to be well-tolerated, the authors note that “future studies should measure oxalate levels and biologically relevant ascorbate levels and determine the optimum dosing regimen that optimizes effect and minimizes potential toxicity.”
In addition to the potential benefits of vitamin C for anemia management, the importance of adequate vitamin C with regard to improving cardiovascular outcomes in MHD patients is also the subject of research. A study by Deicher and colleagues of 138 incident MHD patients examined baseline levels of plasma vitamin C and followed the cohort for occurrence of cardiovascular event (J Am Soc Nephrol 2005;16:1811-1818).
Results showed that low total vitamin C plasma concentrations (less than 32 μmol/L) were associated with an almost fourfold increased risk for fatal and major nonfatal cardiovascular events compared with MHD patients who had higher plasma vitamin C levels (greater than 60 μmol/L).
With 10%-25% of MHD patients thought to be vitamin C-deficient (i.e., less than 10 μM) due to “dietary restriction, concerns about oxalosis, losses during dialysis and accelerated catabolism” (Nephrol Dial Transplant 2007;22:328-331), practice considerations include the need for routinely prescribed renal multivitamins, strategies to improve patient usage, and ongoing research to determine adequate serum vitamin C levels and the potential benefits of supplementation.