Researchers looked at the grape juice supplement's effects on the activity of NADPH oxidase in white blood cells (neutrophils), the main producer of the superoxide anion that may significantly increase oxidative stress.
Oxidative stress has been linked to an increased risk of various diseases including cancer, Alzheimer's, and cardiovascular disease.
The effects of the grape juice supplement or a vitamin E supplement were studied in haemodialysis patients since this procedure is "well-recognised" to activate NADPH oxidase in neutrophils, said the researchers from Madrid's Hospital Ramon y Cajal, the Universidad de Alcala, and CIBER Fisiopatologia Obesidad y Nutricion.
The results are published in this month's issue of the American Journal of Clinical Nutrition .
Study details Thirty-two haemodialysis patients were randomly assigned to receive supplements of vitamin E and/or the red grape juice, a placebo, or no supplementation for two weeks.
At the end of the study, lead author Patricia Castilla reports that only the red grape juice supplement was associated with lowed blood levels of total cholesterol and apolipoprotein B (apoB).
ApoB is the main apolipoprotein of LDL cholesterol and is responsible for the transport of cholesterol to tissues.
In high concentrations it has been linked to plaque formation in the blood vessels, although the mechanism behind this is not clear.
Furthermore, the red grape juice also increased HDL cholesterol levels.
Both active supplements reduced the activity of neutrophil NADPH oxidase ex vivo , as well as reducing blood levels of oxidised LDL-cholesterol.
When the supplements were used together the "effects were intensified," said the researchers.
"Regular ingestion of concentrated RGJ by haemodialysis patients reduces neutrophil NADPH-oxidase activity and plasma concentrations of oxidized LDL and inflammatory biomarkers to a greater extent than does that of vitamin E," wrote the researchers.
"This effect of RGJ consumption may favor a reduction in cardiovascular risk."
Building on earlier studies The same researchers report in the same journal in 2006 initial results of their studies with the red grape juice and heart health.
Both healthy and hemodialysis patients were used in that earlier study, and the researchers reported that, in addition to reductions in markers of inflammation levels of plasma monocyte chemoattractant protein 1 (MCP-1), an inflammatory biomarker associated with CVD, were reduced by 56 per cent at the end of the supplementation period.
To read NutraIngredients.com's reporting of the earlier study, click here .
Sports nutrition Grape juice and grape extracts have previously been linked to improvements in oxidative stress markers after excessive exercise.
High intensity exercise can bring on oxidative stress, where free radicals attack tissue and increase ageing.
In 2006 researchers from San Antonio Catholic University in Spain, showed that a drink containing black grape, raspberry and red currant concentrates reduced protein oxidation by 23 per cent following excessive exercise.
Similar tests for a placebo crossover showed protein oxidation increased by 12 per cent ( Clinical Nutrition , doi: 10.1016/j.clnu.2005.11.007).
Moreover, Berkem - now part of Naturex - reported that supplements of a polyphenol-rich Bordeaux grape extract increased power during exercise by 21 per cent.
Their Powergrape ingredient is being marketed to the sports nutrition market.
Source: American Journal of Clinical Nutrition April 2008, Volume 87, Pages 1053-1061 "Comparative effects of dietary supplementation with red grape juice and vitamin E on production of superoxide by circulating neutrophil NADPH oxidase in hemodialysis patients" Authors: P. Castilla, A. Davalos, J.L. Teruel, F. Cerrato, M. Fernandez-Lucas, J.L. Merino, C.C. Sanchez-Martin, J. Ortuno, M.A. Lasuncion