Gary D. Stoner of the Ohio State Comprehensive Cancer Center fed rats an anthocyanin-rich extract of black raspberries and found that the extract was nearly as effective in preventing esophageal cancer in rats as whole black raspberries containing the same concentration of anthocyanins.

This study demonstrates the importance of anthocyanins as preventive agents in black raspberries and validated similar in vitro findings, Stioner said.

"Our data provide strong evidence that anthocyanins are important for cancer prevention," Stoner said in a statement.

Stoner and his colleagues have conducted clinical trials using whole berry powder, which has yielded some promising results, but required patients to take up to 60 grams, or 2.1 ounces, of powder a day.

"Now that we know the anthocyanins in berries are almost as active as whole berries themselves, we hope to be able to prevent cancer in humans using a standardized mixture of anthocyanins," said Stoner.

The findings are published in the journal Cancer Prevention Research.