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Berries Seem to Burst with Cancer Protection

Gary Stoner, PhDBerries may be among the most beneficial fruits to eat for cancer prevention. Scientists are beginning to find out why.

Research is providing new evidence that berries not only contain strong antioxidants that help to prevent cell damage that precedes cancer: they also appear to affect genes that are associated with inflammation and the growth of cancer.

What the Studies Show

Gary Stoner, PhD, professor at the Medical College of Wisconsin, has been studying the potential of berries for cancer prevention for more than two decades.

In his studies, Dr. Stoner found that a diet of freeze-dried black raspberries or strawberries can inhibit esophageal cancer in rats 30-70 percent and colon cancer up to 80 percent. In these studies, the berries were freeze-dried then ground into a powder.

From recent early phase clinical studies, Dr. Stoner and his colleagues found that black raspberry and strawberry powders are safe and well tolerated. His current pilot studies are focusing on people who are at high risk for cancer to explore whether black raspberry and strawberry powder might slow growth of precancerous lesions among people who are at high risk.

The Science

Berries contain a group of phytochemicals called "polyphenols." Two particularly active types of these anti-cancer compounds that work together are:

  • anthocyanins, a class of flavonoids that gives berries their color
  • ellagitannins, the source of ellagic acid

Berries also contain simple phenols such as quercetin and ferulic acid and they are loaded with vitamin C, the mineral manganese, plus dietary fiber.

In one study, patients diagnosed with an inherited condition that increases their risk for colon cancer were given black raspberry powder mixed with water to drink and in the form of rectal suppositories for nine months. The study found a 36 percent regression of rectal polyps in these patients.

Berries and Breast Cancer

Animal studies on the effect of blueberries and black raspberries on estrogen-positive breast tumors have shown good potential as well. AICR grantee Harini Aiyer, PhD, Postdoctoral Research Fellow at Lombardi Cancer Center, Georgetown University School of Medicine, found that a six-month diet of black raspberries reduced breast tumor volume in rats by 70 percent. A six-month diet of blueberries reduced tumor volume by 60 percent.

Harini Aiyer, PhD

In cell culture studies, Dr. Aiyer also found that adding ellagic acid to estrogen-positive cells treated with tamoxifen made them less likely to become resistant to the effects of the drug. Although promising, further studies are needed.

"If estrogen acts as fuel for some breast cancers, we may be able to use ellagic acid, which acts like an anti-estrogen, to cut off the fuel supply," says Dr. Aiyer.

Enjoy a Variety of Berries

While berries' protective effects on humans are still being studied, Drs. Stoner and Aiyer both suggest eating 4-5 servings of berries per week. Fresh, unsweetened frozen or canned berries are all good choices.

"There may be merit to mixing berry types," says Dr. Stoner. "They may not do things the exact same way, but they all seem to have a positive effect."

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