The effects and toxicity of vitamin C supplementation in stable hemodialysis outpatients

Abstract

The present study was undertaken to evaluate the effects and toxicity of vitamin C supplementation (VCS) in 61 clinically stable hemodialysis outpatients.
All patients were given VC, 500mg daily, for 2 years and observed for a further 2 years without VCS. VCS significantly increased plasma levels of ascorbic acid up to 7.8mg/dl (mean 3.3±0.4 SEM) which fell after withdrawal to within the normal range (mean 1.2±0.2mg/dl). Hyperoxalemia was aggravated by VCS (mean 61.5±3.3μmol/l, range 33.3 to 165.5) while plasma oxalate levels in the unsupplemented period decreased to 36.3±3.3μmol/l, (p<0.01). There was no difference in creatinine, hematocrit, blood transfusion requirement, morbidity (including hospitalisation) or mortality between the two periods of time in the same patients. In conclusion, we could not find any beneficial efects on morbidity or mortality as a result of using VCS in stable hemodialysis outpatients, however, secondary hyperoxalemia was aggravated. As a result of these observations it appears that VCS is harmful and unnecessary in these patients provided they are on an adequate diet.