RESUMEN
PURPOSE: Whey protein has antioxidant properties through its amino acid cysteine, which enhances the biosynthesis of glutathione, the most abundant antioxidant non-protein in mammalians. Glutathione influences vitamin C recycling and increases its protective effect on oxidative stress (OS). The aim of this study was to analyse the effect of whey protein and vitamin C supplementation on OS biomarkers in chronic haemodialysis (HD) patients. METHODS: This pioneer trial was a randomised, double-blind, pilot study in patients from a dialysis clinic. Patients were randomised into three groups (1:1:1) and stratified by HD frequency (2 or 3 times/week). Sachets containing protein powder (20.0 g) with/without vitamin C (0.25 g) or placebo (20.0 g of white rice flour) with vitamin C (0.25 g) were supplemented after each HD session, 3 times/week for 8 weeks. Blood samples were collected at the baseline period and after 8 weeks for the measurement of reduced glutathione (GSH), oxidised glutathione (GSSG), the GSH:GSSG ratio, malondialdehyde, vitamin C, and glutathione peroxidase-1. RESULTS: Twenty-two patients were enrolled, of which 18 concluded the trial, 6 per group (18.2%, n = 4 losses during follow-up). The vitamin C group presented decreased GSH levels after supplementation (p = 0.053) and a decreasing tendency in the GSH:GSSG ratio (non-statistically significant), while MDA levels significantly decreased only in the whey protein-supplemented groups (p ≤ 0.05). CONCLUSION: The results suggest a pro-oxidant effect of 0.25 g of vitamin C alone in chronic HD patients. CLINICAL TRIAL REGISTRATION: https://ensaiosclinicos.gov.br/ , RBR-65b8f4.