Scientists from the University of California, Davis, carried out the first human clinical trial of grape seed extract with people suffering from metabolic syndrome (MetS), a condition that affects an estimated 40 per cent of the US adult population.
MetS is a condition characterised by central obesity, hypertension, and disturbed glucose and insulin metabolism. The syndrome has been linked to increased risks of both type 2 diabetes and CVD.
The new research, presented at last weekend's American Chemical Society Meeting and Exposition in Atlanta, divided 20 male and female volunteers with diagnosed MetS into three groups, and supplemented their normal diets with a placebo, or grape seed extracts with 150 or 300 milligrams of extract.
After one month, all participants taking the supplements had a significant decrease in both systolic and diastolic blood pressure.
"Participants in the two groups receiving grape seed extract experienced an equal degree of reduced blood pressure. The average drop in systolic pressure was 12 mm Hg. The average drop in diastolic pressure was eight mm Hg," said lead author Tissa Kappagoda.
While both extracts produced similar decreases in blood pressure, the scientists observed that the 300 mg extract also reduced blood levels of oxidised LDL-cholesterol, which ahs been linked to an increased risk of heart disease by a variety of experimental, genetic and epidemiological studies.
"Generally, the higher the initial oxidised LDL level was, the greater the drop by the end of the study," said Kappagoda.
Grape seed extracts are rich sources of antioxidants such as catechins and flavan-3-ols, and subsequent dimmers, trimers, and tetramers. These polyphenols compounds are found in highest concentrations in the seed of grapes, which can contain as much as eight per cent polyphenols by weight.
The proposed mechanism of antioxidant activity of grape seed extract involves intercepting the damaging free radicals that are produced by oxidation of LDL-cholesterol.
The extracts, supplied by Polyphenolics, a division of Constellation Wines US, who also funded the study, have already received the generally recognised as safe (GRAS) certification from the FDA.
The news comes hot-on-the-heels of similar positive results for grape seed extracts, with Masquelier's Original OPCs (oligomeric proanythocyanidins), Anthogenol, being reported to reduce free radical damage of endothelial cells (cells that line the wall of blood vessels).
Recent ex vivo experiments by Japanese researchers reported that Anthogenol reduced oxidative stress of cell cultures by 60 per cent.