But when the body's system for processing estrogen gets out of balance, dangerous estrogen metabolites appear. These toxic compounds react with DNA in breast cells and jump-start the growth of tumors.
Now Eleanor G. Rogan, PhD, and colleagues at the University of Nebraska show that resveratrol decreases the processing of estrogen into these dangerous compounds. Perhaps more importantly, it also blocks interactions between estrogen metabolites and cellular DNA.
And that's not all. Rogan's team finds that resveratrol increases production of an enzyme that destroys dangerous estrogen metabolites.
"Resveratrol has the ability to prevent the first step that occurs when estrogen starts the process that leads to cancer," Rogan says in a news release. "We believe that this could stop the whole progression that leads to breast cancer down the road."
Even so, there's a hopeful sign: Resveratrol had anticancer effects at very low doses.
"This is dramatic because it was able to be done with fairly low concentrations of resveratrol," Rogan says.
A resveratrol concentration of 10 micromoles per liter was able to keep estrogen metabolites from interacting with DNA. A glass of red wine has a resveratrol concentration between 9 and 28 micromoles per liter.
However, a 2007 study in the U.K. suggested that even very high doses of resveratrol do not achieve blood concentrations as high as those needed for anticancer effects.
Resveratrol is a naturally occurring antioxidant found in the skins of red grapes, red wine, red or purple grape juice, peanuts, blueberries, and cranberries. It's also available in dietary supplements.
Although many health claims have been made for resveratrol, the risks and benefits of taking this supplement have not been formally tested in definitive clinical trials.
Rogan and colleagues report their findings in the July issue of Cancer Prevention Research.