Data suggest that ascorbic acid can improve responsiveness to erythropoietin in anemic patients.
The importance of adequate vitamin C, or ascorbic acid, as an antioxidant and in collagen synthesis is well-established; however, there are special concerns with regard to avoiding excessive amounts in CKD.
Current recommendations for maintenance hemodialysis (MHD) patients advise supplementation with ascorbic acid 75-90 mg daily (Nephrol Dial Transplant. 2007;22[Suppl 2]:ii45-ii87) to replace the losses of this water-soluble vitamin that occur during dialysis.
This amount of vitamin C is found in most renal multivitamins, i.e., vitamin combinations prescribed specifically to need the needs of MHD patients, though estimates from the Dialysis Outcomes and Practice Patterns Study (DOPPS) indicate that renal multivitamins are prescribed for only about 70% of dialysis patients in the United States (Am J Kidney Dis. 2004; 44[5 Suppl 2]:61-67).
Regarding the benefits of renal multivitamin use, the authors report that “patients taking such vitamins had a 16% lower mortality risk than patients not taking water-soluble vitamins, after adjustment for age, sex, race, comorbid conditions, hemoglobin, serum albumin, body mass index, time on HD, average facility single-pool Kt/V, and average facility normalized protein catabolic rate.” Since dietary sources of vitamin C are often restricted because of concerns about potassium, a daily renal multivitamin can be an important part of standard care for dialysis patients.
Because vitamin C is excreted by the kidney, intake greater than 100-200 mg/day should be avoided in CKD to avoid oxalosis, which is the accumulation of the metabolic by-product of ascorbic acid. Many organs and tissues of the body can be affected by oxalate deposits, including the kidneys.
Cases of acute renal failure (ARF) have been documented. Recently, Nankivell and Murali reported oxalosis resulting in graft failure in a kidney transplant recipient who had been taking self-prescribed doses of vitamin C 2,000 mg daily as a dialysis patient for the three years prior to transplant (N Engl J Med. 2008;358:e4).
Similarly, a case report by McHugh and colleagues (Anaesth Intensive Care. 2008;36:585-588) describes mortality from vitamin C-induced ARF. Oxalosis was confirmed on autopsy in this patient, who, unbeknownst to physicians, had been ingesting “several grams per day” of vitamin C in the belief that it would be beneficial for his health.