Antioxidants are believed to prevent many types of disease. Some previous studies have suggested that dietary supplementation with vitamin C results in a decrease in the level of one of the markers of oxidative damage, 8-oxoguanine, in the DNA of peripheral blood mono-nuclear cells (PBMC). UK investigators investigated the effect of different dose levels of dietary supplementation with vitamin C on oxidative DNA damage. A double-blind placebo-controlled RCT was carried out using three different levels (80, 200 and 400 mg) of dietary vitamin C supplementation in a healthy population of 160 volunteers; supplementation was for a period of 15 weeks followed by a 10-week washout period. Peripheral blood samples were obtained every 5 weeks from baseline to 25 weeks. An increase in PBMC vitamin C levels was not observed following supplementation in healthy volunteers. There was no effect found on 8-oxoguanine measured using HPLC with electrochemical detection for any of the three supplemented groups compared to placebo. 8-oxoadenine levels were below the limit of detection of the HPLC system used.