Researchers at the University of California, Irvine report that the benefits appear to go beyond that of resveratrol alone, the polyphenol often touted as the bioactive compound in grapes and red wine.
The benefits, possibly due to synergistic effects between the grape compounds, were observed to occur by blocking a cellular signalling pathway known as the Wnt pathway, linked to more than 85 per cent of colon cancers.
The results are set to be presented tomorrow in San Francisco at the Society for Integrative Oncology's Fourth International Conference.
"This is truly exciting, because it suggests that substances in grapes can block a key intracellular signalling pathway involved in the development of colon cancer before a tumour develops," said Dr. Randall Holcombe, lead researcher on the study.
Building on previous in vitro studies using exclusively resveratrol, Holcombe at co-workers recruited colon cancer patients and randomly assigned them to receive a resveratrol pill (20 milligrams per day), or a beverage of grape powder in water (80 or 120 grams of powder per day).
The resveratrol supplements were not associated with any effect on colon tumours.
However, tissue samples from the colon of patients receiving the low dose grape powder drink showed significant reductions in Wnt signalling.
Curiously, no effects were observed at the higher dose beverage.
Previous studies have linked resveratrol to having a positive effect on extending survival rates of mice and preventing the negative effects of high-calorie diets.
It has also been linked to diabetes, heart health and obesity.
Resveratrol - an antioxidant - is also found in raspberries, peanuts and blueberries, which in turn fall under the umbrella group of superfoods.
In red wine, the amount of resveratrol in a bottle can vary between types of grapes and growing seasons, and can vary between 0.2 and 5.8 milligrams per litre.
But nearly all dark red wines - merlot, cabernet, zinfandel, shiraz and pinot noir - contain resveratrol.
Holcombe and co-workers state that they are uncertain as to why the lower dose of grape powder was more effective than the higher one.
Work is ongoing in the field, and Holcombe confirmed that a clinical cancer prevention study is currently under design to see how a daily diet of 80 grams of grapes affects Wnt signalling.
The pilot study follows an epidemiological survey by UC Irvine researchers investigating the wine consumption habits of 499 colorectal cancer patients.
The study, published recently in the journal Nutrition and Cancer, reported that moderate wine consumption was associated with improved survival statistics.
Indeed, 75 per cent of such patients were alive after 10 years of initial diagnosis, compared to 47 per cent of such patients who did not regularly drink wine.
"Our epidemiologic study suggests that wine consumption may influence survival among a subset of colorectal cancer patients, specifically those with family history of the disease," said Dr. Jason Zell, co-authors of the epidemiological study.
"These findings could reflect unique genetic and environmental interactions among familial colorectal cancer patients, but further studies are needed to test this theory.
Studies such as Dr. Holcombe's with grape powder extract and resveratrol are important as they offer potential explanations for our findings."
"These findings suggest that we should do additional research and clinical studies on grapes and other natural products that may prove effective in helping to prevent cancer," he said.
Colorectal cancer accounts for nine per cent of new cancer cases every year worldwide.
The highest incidence rates are in the developed world, while Asia and Africa have the lowest incidence rates.
It remains one of the most curable cancers if diagnosis is made early.
Source: Society for Integrative Oncology's Fourth International Conference Clinical Botanical Research: Session IV, November 16, 2007 "Freeze dried grape powder inhibits a panel of Wnt pathway target genes in normal colonic mucosa: Results of a pilot trial in patients with colon cancer" Authors: R.F. Holcombe, M. Stamos,C. Hope, K. Planutis, A.V. Nguyen, A. Crase, S. Sakowsky