Studies have not established the effect of rhubarb on breast cancer
Rhubarb is a good source of vitamin C, calcium, magnesium and dietary fiber. Rhubarb contains the carotenoids lutein and zeaxanthin, which have been shown to have some anticancer activities. Rhubarb has also been shown to have anti-inflammatory, anti-atherosclerosis and plaque-stabilizing actions in laboratory animals.
Cancer-related effects of eating rhubarb
Rhubarb contains the polyphenol (Z)-3,5,4-Trimethoxystilbene, a resveratrol analog that has been shown to arrest the growth of human colon cancer cells in a dose dependent manner. Piceatannol, another polyphenol in rhubarb, has been shown to exert immunosuppressive, antileukemic, and antitumorigenic activities, including inhibition of the proliferation of human bladder and prostate cancer cells. The most abundant anthraquinone of rhubarb, emodin (which has traditionally been used as a laxative) has been shown to induce apoptosis in human pancreatic, liver, prostate and breast cancer cell lines. Rhein, another component of rhubarb, has been found to induce apoptosis of nasopharyngeal cancer cells. Because rhubarb typically does not comprise a large portion of the diet of any group of people, there are no population-based studies that specifically isolate any associations between consuming rhubarb and the risk of cancer.
Additional comments
Rhubarb is a component of Essiac™ tea, a herbal tea sometimes used as a cancer treatment. While the tea has been shown in the laboratory to have potent antioxidant and DNA-protective activity, one careful study found no observable action of Essiac™ against prostate cancer cells.
Rhein, a constituent of rhubarb, is the major component of several traditional Chinese herbal medicines, including laxatives and stomach remedies. Rhein herb-drug interactions, especially cytochrome P450 (CYP)-mediated interactions, may cause an enhancement or attenuation in the efficacy of prescription drugs.
There are some available rhubarb-based herbal remedies designed to treat menopausal symptoms in women and containing the phenolic gallylglucoside lindleyin. Lindleyin is a phytoestrogen which has demonstrated estrogenic activity. We recommend against using such remedies for breast cancer patients, survivors and those at high risk for breast cancer since their safety has not been demonstrated. In particular, it is possible that lindleyin could promote beast cancer through its estrogenic activity. Rhubarb should not be consumed by pregnant women since it may trigger uterine contractions.
Consuming large amounts of rhubarb to obtain the possible benefit of its anticancer components would be impractical since a great deal of sweetener is required to counteract rhubarb's sourness and since the gastrointestinal effects could be overwhelming. However, we would not recommend consuming concentrated rhubarb extracts or pills since their safety and efficacy have not been established.
Rhubarb leaves should not be consumed since they are poisonous. People with a history of kidney stones should avoid rhubarb, since consumption of rhubarb has been shown to increase urinary oxalate due to the plant's relatively high oxalate content.
Note that while we are continually searching for new evidence specifically concerning this food, there is not much interest in it among breast cancer researchers, so few studies are available.