Polyphenols, antioxidant phytonutrients such as resveratrol, anthocyanins, catechins, and quercetin, are believed to help the body's cells resist damage by free radicals. The same disease-fighting properties are thought to be delivered by both fresh grapes and red wine.
In the current study, however, the researchers from the University of Connecticut and Columbia University used a lyophilized grape powder consisting of 92 percent carbohydrate and rich in flavans, anthocyanins, quercetin, myricetin, kaempferol, and resveratrol.
They set out to evaluate the effects of grape polyphenols on key risk factors for coronary heart disease in pre- and post-menopausal women.
Heart disease is traditionally thought of as affecting more men than women, but in fact it is the number one killer of women in America, according to the American Heart Association.
In 2002 493,690 women in the US died of heart disease, compared with 256,503 for all forms of cancer combined.
The study, published in the August issue of the Journal of Nutrition (135:1911-1917), involved 24 pre-menopausal women and 20 post-menopausal women, who were assigned to one of two groups.
For the first four-week period, one group consumed 36g of lyophilized grape powder, and the other received a placebo with an equal ratio of fructose and dextrose and energy content similar to the grape powder (554KJ).
After a three-week washout, the two groups were switched for a second four-week period.
Plasma triglyceride concentrations were reduced by 15 percent in the pre-menopausal women after they had taken the grape powder, and 6 percent in the post-menopausal women. Plasma LDL ('bad') cholesterol and apolipoproteins B and E were also lower with the grape powder, and cholesterol ester transfer protein activity was decreased by around 15 percent.
The grape powder did not appear to affect LDL oxidation, but whole-body oxidative stress was "significantly reduced", and levels of plasma tumor necrosis factor-alpha, which is associated with inflammation also decreased.
These observations caused the researchers to conclude: "Through alterations in lipoprotein metabolism, oxidative stress, and inflammatory markers, LGP intake beneficially affected key risk factors for coronary heart disease in both pre- and postmenopausal women."
This is not the first time the benefits of grape polyphenols have been observed by the Connecticut research team. In 2003, the Journal of Nutrition published an earlier study whereby female guinea pigs that had had their ovaries removed were used as a model for menopausal women.
In this instance, the guinea pigs were fed either a control diet or a diet containing grape powder for 12 weeks. The results bore similarities to those observed in the human subjects - that is, in the grape powder group plasma triglycerides were 39 per cent lower, very low density lipoprotein (VLDL) cholesterol was 50 per cent lower, phospholipids were 30 per cent lower and concentrations of cholesterol in the aorta were 33 per cent lower.
Blood levels of LDL cholesterol concentrations did not differ between groups.