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. 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. A methanolic extract of fennel was shown to be cytotoxic to human melanoma cells in one study. 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. 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, fennel seed tea or fennel essential oil.
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.
Selected studies
A striking and frequent cause of premature thelarche in children: Foeniculum vulgare Journal of Pediatric Surgery, November 2008The present journal article describes a connection that has been found between use of Foeniculum vulgare (fennel) preparations and premature thelarche. Premature thelarche is characterized by breast development in infants and young children with no other signs of puberty. Although it is normally caused by adrenal or ovarian hormonal disorders, hypothyroidism, or use of exogenous hormones or drugs, premature thelarche may also be associated with long-term use of herbal medicine. Long-term use of preparations such as Foeniculum vulgare, which is used to reduce colic, help eliminate gas, and regulate intestinal function in children, may cause premature thelarche. The use of such preparations should be limited, according to the authors.
Cytotoxic and xenoestrogenic effects via biotransformation of trans-anethole on isolated rat hepatocytes and cultured MCF-7 human breast cancer cells Biochemical Pharmacology, July 2003
The current study was designed to investigate the impact of trans-anethole (anethole), a component of fennel, on metabolism, and to evaluate the estrogen-like activity of anethole and its metabolites. These were studied in freshly isolated rat hepatocytes and MCF-7 human breast cancer cells. Incubation of hepatocytes with anethole (0.25–2.0 mM) was found to result in concentration- and time-dependent cell death, accompanied by loss of cellular ATP and reduction in adenine nucleotide pools. Anethole at a weakly toxic level (0.5 mM) was found to be metabolized to 4-methoxycinnamic acid (4MCA), 4-hydroxy-1-propenylbenzene (4OHPB), and the monosulfate conjugate of 4OHPB. 4OHPB was found to be more toxic than either anethole or 4MCA, based on effect on cell viability and adenine nucleotide levels. The addition of 2,6-dichloro-4-nitrophenol (50 μM), an inhibitor of sulfotransferase, was found to heighten the anethole-induced cytotoxicity associated with losses of ATP, PAPS, and 4OHPB sulfate, and symmetrically increased the unconjugated 4OHPB concentration. Like diethylstilbestrol (DES) and bisphenol A (BPA), which are known estrogenic compounds, 4OHPB competitively displaced 17β-estradiol bound to the estrogen receptor alpha in a concentration-dependent manner. 4OHPB also was found to induce concentration-dependent proliferation of MCF-7 breast cancer cells, whereas neither anethole nor 4MCA influenced cell proliferation. However, at high concentrations, 4OHPB was cytotoxic (unlike anethole and 4MCA). The authors conclude that the anethole induces a cytotoxic effect at higher concentrations in rat hepatocytes and an estrogenic effect at lower concentrations in MCF-7 cells based on the concentrations of the hydroxylated intermediate, 4OHPB.
