Studies have not established the effect of fennel on breast cancer
Fennel (Foeniculum vulgare) belongs to the umbelliferae family, which also includes carrots, celery, dill, parsnips, parsley, cumin, and coriander. All parts of the fennel plant are edible (bulb, stalk, leaves and seeds). Fennel is a good dietary source of vitamin C, potassium, and fiber, and a fair source of folate, manganese, and molybdenum. Fennel also contains various phytochemicals, including limonene, rutin, quercetin, and kaempferol, all of which have demonstrated chemopreventive activities. Fennel contains the terpenoid anethole, which has been reported to have both estrogenic and chemopreventive effects, as well as estragole, which acts as a rodent carcinogen in large doses. Fennel has been shown to have antioxidant, antifungal, antibacterial and antithrombotic properties.
Fennel seed tea and other fennel preparations have been used in some traditional medicine systems to sooth colic in babies, and to help expel gas and treat indigestion in adults. Other traditional uses include enhancing breast milk production, promoting menstrual flow, easing childbirth, and inducing abortion. Methanolic extracts of fennel have been shown to be cytotoxic to human melanoma, live cancer and breast cancer cells. A fennel seed diet was shown to prevent carcinogen-induced skin cancer in mice in another study.
Breast cancer-related effects of consuming fennel
Information concerning fennel consumption as it relates to risk of breast cancer is limited. Fennel seed is a very good source of melatonin, which protects against breast cancer in several ways, including by reducing aromatase activity within the breast, thereby reducing estrogen production. However, reports that fennel has been used to increase breast milk production are concerning because they suggest that fennel acts directly on breast tissue. Fennel has been shown to have estrogenic and progesterone-binding properties, although not all studies agree on this. Until more information becomes available, it appears inadvisable for breast cancer patients, survivors and those at high risk to consume more than modest amounts of fennel, fennel seed, or fennel seed tea. Fennel oil should be avoided.
Additional comments
Women who are pregnant or nursing should not consume fennel or fennel seed since fennel can stimulate the uterus.
Fennel has been shown to impair the absorption of the antibiotic ciprofloxacin (Cipro) and in all likelihood would interfere similarly with other fluoroquinolone antibiotics. Consuming fennel can also interfere with Warfarin (coumadin) and other blood-thinning therapy since it is a source of a plant coumarin.
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.