Black raspberries may contain compounds that prevent esophageal cancer and keep precancerous growths from becoming malignant.

According to the report rats injected with a cancer-causing compound were less likely to develop cancer of the esophagus when black raspberries comprised 5% to 10% of their daily diet. The findings add to a growing body of evidence linking berries with lower cancer risk.

Raspberries contain many vitamins, minerals, plant compounds and antioxidants known as anthocyanins that may protect against cancer. While it is not clear how these compounds fight off cancer, the researchers recommend that individuals include a serving of fresh or frozen berries in their daily diet.

In the study, researchers injected rats with NMBA, a chemical that has been shown to cause esophageal cancer. Some rats consumed a diet comprised of 5% to 10% black raspberries before and/or after receiving injections, while other rats were fed diets that did not include raspberries.

Rats that consumed the greatest amount of black raspberries both 2 weeks before and up to 30 weeks after NMBA injections had 49% fewer tumors than rats whose diets did not include black raspberries, the researchers report.

Additionally, tumors that had developed in rats fed raspberries only after receiving the injections were found to decrease in size after 15 weeks.

After 25 weeks, rats fed diets of 5% to 10% black raspberries saw the number of esophageal tumors decrease by 43% to 62%. A diet containing 5% black raspberries was more effective than a diet containing 10% black raspberries.

There may be a threshold over which protective compounds such as antioxidants, which normally neutralize disease-causing free radicals, actually damage DNA in the presence of a carcinogen like NMBA.

Esophageal cancer is the fifth leading cause of cancer death in the world, according to the report. Just 8% to 12% of individuals will survive 5 years after being diagnosed with the disease.

Cancer Research 2001;61:6112-6119