The effects of vitamin C supplementation on biomarkers of oxygen radical generated damage in human volunteers with “low” or “high” cholesterol levels

Abstract

A human volunteer study was conducted to test the effect of vitamin C supplementation on biomarkers of oxygen radical-mediated damage in individuals with a range of serum cholesterol levels. A group of 48 non-smokers, 24 men and 24 women, was selected from a panel of over 100 volunteers to give as wide a range of serum cholesterol levels as possible. None of the volunteers was taking medication to control cholesterol levels and they maintained their normal dietary habits so as not to compromise their cholesterol status. Volunteers were allocated to three groups of 16, each consisting of four males with low cholesterol levels (< 6 mmol/L) matched for age and build with four males with high cholesterol levels (> 6 mmol/L) and eight females matched in the same way. A three-treatment, three-treatment period, cross-over design was adopted to take account of any temporal differences in response. The three treatments given were placebo, 60 mg vitamin C/day (the recommended daily allowance) and 6 g vitamin C/day. Each treatment was given for 14 days with 6 weeks between the treatment periods. All procedures were performed to the standards of Good Clinical Practice. Blood samples were taken at the end of each treatment period. Serum was assayed for cholesterol whilst vitamin C, total antioxidant capacity, lipid peroxidation breakdown products and ras p21 protein levels were measured in plasma. Lymphocytes were examined for DNA damage using the Comet assay and chromosome aberration test. The Comet assay was conducted with and without challenge with hydrogen peroxide and the chromosome aberration test with and without challenge with bleomycin. Vitamin C supplementation caused a statistically significant increase in plasma vitamin C concentrations and total antioxidant capacity but did not affect cholesterol levels or ras p21 protein levels. There was a non-significant dose-related decrease in lipid peroxidation breakdown products with vitamin C supplementation. No effect on DNA damage was observed in the Comet assay, either with or without hydrogen peroxide challenge, or in the chromosome aberration test without bleomycin. However, a statistically significant increase in bleomycin-induced aberrations was found after vitamin C supplementation. This may be due to effects of vitamin C on iron status. Comparison of male and female subjects showed statistically significant differences in plasma vitamin C levels, the antioxidant capacity of the plasma and the number of chromosome aberrations induced by bleomycin challenge of lymphocytes in vitro. The results were the same for both low and high cholesterol subjects. This study provides no evidence of a beneficial effect on any of the biomarkers studied of vitamin C supplementation over a short-term supplementation period of 2 weeks in a population of healthy, non-smoking individuals eating a nutritionally adequate diet.

Protective effect of vitamin C on 8-hydroxy-2′-deoxyguanosine level in peripheral blood lymphocytes of chronic hemodialysis patients

“…Some investigators have reported a reduction in ex vivo or in vivo DNA oxidation in lymphocytes after vitamin C supplementation in healthy volunteers [25,35,36], whereas others have shown no change [37] or even yielded mixed results with a decreased in some types of oxidized DNA bases and an increase in others [38,39]. However, this inconsistency is likely due to technical problems associated with gas chromatography-mass spectrometry analysis in some studies [38,39].…”

Does vitamin C act as a pro‐oxidant under physiological conditions?

“…More recently, the comet assay has been gaining acceptance due to its capacity to detect low levels of basal DNA damage without artifactual oxidation (48,57,58) (Table 2). A recent study examined DNA damage in lymphocytes with this assay (57). Nonsmoking subjects were given placebo, 60 and 6000 mg/day of vitamin C for 2 wk each, with 6 wk in between treatment periods.…”

Does Dietary vitamin E or C Decrease Egg Yolk Cholesterol?

“…Vitamin C has been shown to significantly reduce lipid peroxide levels [39] and protect LDL-C from oxidation, thus facilitating LDL's normal binding to membrane receptors on the liver and therefore expedite its removal from the blood by LDL-C catabolic pathways. However, some researchers reported that vitamin C did not protect plasma lipids [40] or LDL [41,42] from oxidation and suggested that this is because vitamin C is hydrophilic and does not bind to lipoproteins [42]. Although the underlying mechanisms are not yet fully understood, it is reasonable to assume that the hypocholesterolemic properties of vitamin C are most profound when total serum cholesterol is very high [43].…”