And the concentrated juice worked for both healthy subjects and hemodialysis patients - the latter are at a higher risk of cardiovascular complications.
Previous research with grape juice has shown that the polyphenol rich juice could reduce the oxidation of LDL (bad) cholesterol.
This led to Gerber Foods, distributor of Welch's purple grape juice in the UK, announcing at the end of 2005 that it had been approved by the heart health charity Heart UK, and now carries the charity's logo on its packaging.
New research from Spain appears to confirm and extend these cardiovascular benefits, reporting positive results of supplemental red grape juice on both healthy subjects and hemodialysis patients.
"We show for the first time that red grape juice supplementation improves the lipoprotein profile by decreasing plasma concentrations of LDL and increasing those of HDL and greatly reduces the plasma concentrations of oxidised LDL and MCP-1, an inflammatory biomarker," wrote the researchers in the American Journal of Clinical Nutrition (Vol. 84, pp. 252-262).
The scientists, led by Miguel Lasuncion from the Biochemical Investigation Service at the Ramon and Cajal Hospital in Madrid, recruited 15 healthy subjects and 22 subjects receiving hemodialysis. Participants were instructed to drink 100 mL of red grape juice concentrate every day for two weeks, and blood samples taken to follow levels of blood lipids and the inflammatory marker, MCP-1.
Three hours after ingestion of the red grape juice, a 25 per cent rise in plasma concentrations of quercetin were recorded, indicating the polyphenols were rapidly absorbed.
It was found that after two weeks of supplementation, both health subjects and hemodialysis patients had reductions in LDL-cholesterol levels, oxidised LDL levels, and total cholesterol levels. Levels of HDL-cholesterol increased for all the red grape juice supplemented subjects.
The ratio of total cholesterol to HDL cholesterol, reported to be the most specific lipid risk factor for CVD, decreased for healthy subjects after both seven and 14 days, compared to baseline (reductions of 0.18 and 0.6, respectively).
Larger reductions in the ratio were observed for the hemodialysis patients, falling by 0.58 after seven days, and 1.14 after 14 days.
CVD causes almost 50 per cent of deaths in Europe, and is reported to cost the EU economy an estimated €169bn ($202bn) per year. According to the American Heart Association, 34.2 per cent of Americans (70.1m people) suffered from some form of cardiovascular disease (CVD) in 2002.
In a separate experiment only for the hemodialysis patients, the researchers investigated the effects of the red grape juice on markers of inflammation by supplement the diets for three weeks with the same dose of the juice used in the other experiments.
It was found that 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.
The mechanism behind the benefits observed is not known, said the researchers. However, no significant changes in serum levels of the antioxidants vitamin E, lycopene, beta-carotene, and vitamin C suggest that grape juice does not function by sparing the other antioxidants.
"Therefore, other antioxidants, probably polyphenols, are likely to be responsible for the observed effects of red grape juice consumption on antioxidant capacity," said the authors.
But the results are in agreement with other studies that have linked red wine consumption, polyphenol-rich green tea or pine bark extracts to improved cardiovascular risk factors.
"Dietary supplementation with concentrated red grape juice exerts hypolipidemic, antioxidant, and anti-inflammatory actions in both healthy subjects and patients with end-stage renal disease," wrote the authors.
"These effects may be considered to be beneficial for the prevention of cardiovascular disease."