Black Cohosh Tied to Breast Cancer Spread

Black Cohosh May Not Promote New Breast Tumors but May Spur Breast Cancer Spread, Lab Tests Show

By Miranda Hitti
WebMD Health News

Reviewed By Louise Chang, MD

Nov. 11, 2008 -- Black cohosh, a supplement taken to ease menopausal symptoms, may have a mixed relationship with breast cancer.

That's according to a study published recently in Cancer Research.

In the study, female mice with a genetic predisposition for breast cancer ate either normal chow or chow laced with black cohosh throughout their adult lives.

The mice in the black cohosh group weren't more likely than the other mice to develop breast cancer. But they were more likely to have their breast cancer spread to their lungs.

That's "concerning," researcher Vicki Davis, PhD, tells WebMD.

Davis, an assistant professor of pharmacology-toxicology at Duquesne University in Pittsburgh, notes that the black cohosh dose used in the study is equivalent to the amount typically recommended for women, but it remains to be seen if the results apply to women, to other types of cancer, and to cancer's spread to organs other than the lungs.

It's also not yet clear if the timing of exposure to black cohosh makes a difference. "Whether we needed black cohosh to be present as the tumors were developing in order for them to be more aggressive, we don't know that," Davis says.

Supplements Industry Responds

Davis' study is "interesting," Andrew Shao, PhD, tells WebMD. He's the vice president for scientific and regulatory affairs at the Council for Responsible Nutrition, a trade group for the supplements industry.

He points out that in Davis' study, the mice were on black cohosh throughout their adult lives, while women typically take black cohosh for several months.

Shao also notes conflicting data about black cohosh and breast cancer. He says some studies suggest that black cohosh "could even reduce the risk of breast cancer" and that "there are no human studies that suggest that it's a problem."

In their paper, Davis and colleagues acknowledge the mixed findings from other studies on black cohosh and breast cancer. But they note issues with some of those studies, such as a lack of a comparison group in a German study of breast cancer patients and a high dose of black cohosh extract used in a study done on cells.

Shao admits that there haven't been any randomized clinical trials to directly test black cohosh for its effects on breast cancer in people.

Shao's advice: "If one does have breast cancer and is looking to try to alleviate some of the symptoms associated with menopause, be in touch with your practitioner, your health care provider. Don't make these decisions in a vacuum."

SOURCES: Davis, V. Cancer Research, Oct. 15, 2008; vol 68: pp 8377-8383. Vicki Davis, PhD, assistant professor, department of pharmacology-toxicology, Duquesne University, Pittsburgh. Andrew Shao, PhD, vice president, scientific and regulatory affairs, Council for Responsible Nutrition.

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