Cruciferous vegetables may lower risk for breast cancer

When your mother told you to eat your vegetables it appears that maternal wisdom had a scientific basis.

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 at Vanderbilt-Ingram, 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 there. 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.

“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.”

While there was only a small positive relationship between a diet high in these vegetables and a reduction in breast cancer risk for the overall study population, there was a striking risk reduction – 50 percent – among women with a certain genetic profile. Researchers identified three forms of the GSTP1 genotype among the cancer patients: Ille/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 called 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., professor of Medicine at Vanderbilt-Ingram 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. “We have published over 100 research papers in this study addressing a large range of significant issues related to the etiology and survival of breast cancer. The results reported by Dr. Fowke may have significant implications in breast cancer prevention.”

While women in this study answered questionnaires about their diets, researchers want to measure more precisely the intake of cruciferous vegetables. To aid in future studies they are collecting urine samples which contain biomarkers for the beneficial chemicals.

Authors for this paper include: Sang-Ah Lee, Wei Lu, Chuangzhong Ye, Ying Zheng, Qiuyin Cai, Kai Gu, Yu-Tang Gao, Xiao-ou Shu and Wei Zheng.