The relationship between grapefruit and breast cancer risk is highly speculative and has to do with how estrogen is metabolized in the body. Elevated levels of estrogen are associated with an increased risk of breast cancer.[1] Normally, the cytochrome P450 enzyme CYP3A4 metabolizes estrogen into a form that is more easily removed from the body. However, grapefruit inhibits this enzyme, raising the question of whether grapefruit might lead to elevated estrogen in the body and potentially an increased risk of breast cancer.
Although biologically plausible, research has not provided a clear answer. In one observational study, higher grapefruit consumption was associated with an increased risk of breast cancer. However, in two other studies, no association was found.[2][3] Furthermore, a study examining the effects of grapefruit on endogenous estrogen levels in postmenopausal women reported unclear and contradictory effects. Whole grapefruit did not affect levels of estrone (E1) or estradiol (E2), while fresh grapefruit juice, bottled juice, and soda all lowered E2 — the opposite of what was hypothesized.[4]
Grapefruit has been reported to increase the plasma concentration of estrogen taken orally.[5] Because grapefruit inhibits CYP3A4 primarily in the intestines rather than the liver,[5] the interaction between grapefruit and estrogen might only be relevant when estrogen is being taken orally, rather than being produced naturally in the body.
References
- ^Key T, Appleby P, Barnes I, Reeves G, Endogenous Hormones and Breast Cancer Collaborative GroupEndogenous sex hormones and breast cancer in postmenopausal women: reanalysis of nine prospective studiesJ Natl Cancer Inst.(2002 Apr 17)
- ^Elizabeth A Spencer, Timothy J Key, Paul N Appleby, Carla H van Gils, Anja Olsen, Anne Tjønneland, Françoise Clavel-Chapelon, Marie-Christine Boutron-Ruault, Marina Touillaud, Maria-José Sánchez, Sheila Bingham, Kay Tee Khaw, Nadia Slimani, Rudolf Kaaks, Elio RiboliProspective study of the association between grapefruit intake and risk of breast cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC)Cancer Causes Control.(2009 Aug)
- ^Kim EH, Hankinson SE, Eliassen AH, Willett WCA prospective study of grapefruit and grapefruit juice intake and breast cancer risk.Br J Cancer.(2008 Jan 15)
- ^Kristine R Monroe, Frank Z Stanczyk, Kathleen H Besinque, Malcolm C PikeThe effect of grapefruit intake on endogenous serum estrogen levels in postmenopausal womenNutr Cancer.(2013)
- ^Weber A, Jäger R, Börner A, Klinger G, Vollanth R, Matthey K, Balogh ACan grapefruit juice influence ethinylestradiol bioavailability?Contraception.(1996 Jan)