"Although there is no direct evidence that any herbal medicines can increase or decrease breast cancer risk, some herbs can have estrogen-like actions and thus raise concern about their long-term use," said Barbour Warren, a research associate with BCERF and the co-author of the fact sheet "Herbal Medicines and Breast Cancer Risk," which is available free on BCERF's Web site at http://envirocancer.cornell.edu/ .
"Some of these substances may prove to have beneficial effects -- and, in fact, may become part of conventional medicine in the future -- but for now, the lack of any regulatory oversight has set up a marketplace for herbal supplements, which is such a mess that women should have lots of reservations in taking these supplements," Warren said.
He points to not only a lack of well-designed clinical trials but also to a lack of any regulations regarding effectiveness or quality control in formulating these supplements and says that women with a high risk of breast cancer should be particularly cautious.
According to Warren, 23 percent of middle-aged women in the United States use herbal medicines, often to treat premenstrual or menopausal symptoms and premenstrual syndrome, to aid in breastfeeding or to decrease breast cancer risk.
Warren reviewed the literature on herbal supplements and breast cancer risk for his report, which was reviewed by two international experts in the field as well as the five scientists on the BCERF staff.
"Just because herbal medicines are 'natural' products does not mean that they are safer than conventional medicines," he said. "The ingredients in herbal medicines can also have adverse effects and lead to