Vitamin C supplementation in kidney failure: effect on uraemic symptoms

Vitamin C (ascorbate) deficiency and symptoms consistent with deficiency (fatigue, myalgia, dyspnoea, gingivitis, cardiovascular instability and depression) are common in patients with renal failure. This study aimed to determine if supplementation with ascorbate in patients with severe renal failure improved symptoms or cardiovascular stability, or was associated with adverse effects.

The study was a 3-month, double-blind, randomized trial of ascorbic acid 250 mg or matching placebo given thrice weekly. Subjects were clinically stable and either received conventional dialysis or had an estimated glomerular filtration rate of <20 mL/min. Symptoms were measured using the Kidney Dialysis Quality of Life-Short Form (KDQOL-SF™) symptom subscale, and the study was 80% powered to detect a change of 10 in the KDQOL-SF™.

Ninety-nine subjects were randomized, and ascorbate deficiency was present in 40% at baseline. Mean symptom scores at follow-up were similar in the two groups (P-value=0.19). There was a trend to slightly worse nausea scores in the ascorbate group after controlling for the level of baseline nausea (P=0.09), and there was no impact on cardiovascular stability. Compliance appeared adequate at 91%, and deficiency was corrected in most (85%) of the subjects in the active treatment group.

This study indicates that ascorbate supplementation does not improve symptoms or cardiovascular stability in those with severe renal impairment, but is associated with a trend towards worse nausea.