March 14, 2008

Study tracks link between cancer, vegetables

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Jay Fowke, Ph.D., is studying the link between a diet rich in certain vegetables and a decreased risk for breast cancer. (photo by Neil Brake)

Study tracks link between cancer, vegetables

Researchers with Vanderbilt-Ingram Cancer Center and the Shanghai Cancer Institute in China have discovered a possible link between a diet rich in certain vegetables and a decreased risk for breast cancer.

The study appears in the March issue of the American Journal of Clinical Nutrition.

Corresponding author Jay Fowke, Ph.D., assistant professor of Medicine, said 3,035 women diagnosed with breast cancer were identified through the Shanghai Cancer Registry. They were closely matched with 3,037 women randomly chosen from the general population.

The women filled out questionnaires about their diet, including consumption of cruciferous vegetables like Chinese cabbage, bok choi and turnips.

Americans typically eat more broccoli, kale and cauliflower in the cruciferous vegetable family.

While there was only a small positive relationship between a diet high in these vegetables and the risk of breast cancer for the overall study population, there was a striking risk reduction — 50 percent — among women with a certain genetic profile.

“Cruciferous vegetables contain some compounds that may have a cancer-inhibitory effect,” explained Fowke. “Here we were able to identify a group of women who seem to particularly benefit from a high intake of these vegetables.”

Researchers identified three forms of the GSTP1 genotype among the cancer patients: Ile/Ile, Ile/Val and Val/Val. “Women who consumed more of these cruciferous vegetables and who also had the Val/Val genetic polymorphism had a lower breast cancer risk. So we cautiously interpreted this as diet being a factor that may reduce the impact of genetic susceptibility in overall breast cancer risk,” said Fowke.

The Vanderbilt-Ingram researchers focused on cruciferous vegetables because they contain two chemicals — isothiocyanates and indole-3-carbinol — which may affect carcinogenesis by triggering cell death or by shifting estrogen metabolism. Studies by other researchers have suggested cruciferous vegetables may reduce the risk of lung, stomach, colorectal and bladder cancers.

“We have known for some time that certain foods, like soy foods, appear to interfere with the development of breast cancer because they contain plant estrogens,” said Fowke.

“The protective effect from cruciferous vegetables in this study was certainly suggestive of a risk reduction, but researchers need to replicate this finding in other studies.”

Scientists were able to isolate the specific genetic profile linked with a positive dietary impact because the women in the study submitted DNA through blood and cheek cell samples. Wei Zheng, M.D., Ph.D., M.P.H., professor of Medicine, is the principal investigator for the Shanghai Breast Cancer study.

“The Shanghai Breast Cancer Study is one of the largest and most comprehensive epidemiological studies conducted to date for this common cancer,” according to Zheng.

Fowke said researchers are a long way from recommending genetic screening for women.

“We are not at the point where we should broadly scan the population for genetic polymorphisms. We are simply trying to understand the interaction between genes and diet and perhaps five or 10 years down the road this information would provide a piece of the cancer puzzle.”