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Eating grapefruit increases breast cancer risk
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Monroe KR, Murphy SP, Kolonel LN, Pike MC. Prospective study of grapefruit intake and risk of breast cancer in postmenopausal women: the Multiethnic Cohort Study. Br J Cancer. 2007 Jul 10; [Epub ahead of print] Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089-9175, USA. AbstractIn vitro and in vivo studies have shown that cytochrome P450 3A4 (CYP3A4) is involved in the metabolism of oestrogens. There is evidence that grapefruit, an inhibitor of CYP3A4, increases plasma oestrogen concentrations. |
COMMENT: This new research suggests that once again, fruit is no necessarily good for you. Postmenopausal women who regularly eat grapefruit are at increased risk of developing breast cancer, US research suggests.
Indeed, the risk appears to be increased by 25-30% for the highest intake of grapefruit of just one quarter (c.60g) per day compared with not ever eating the fruit.
K Monroe (University of Southern California, Los Angeles) and colleagues used prospective data from the Hawaii-Los Angeles Multiethnic Cohort to determine the effect of grapefruit intake on breast cancer risk in women who had stopped menses naturally or following an oophorectomy.
This study involved over 118,000 women, and asked about their dietary intake of certain foods. The team identified 1657 incident cases of breast cancer in this cohort of African-American, Japanese-American, Latino, Native Hawaiian, and Caucasian women.
Monroe and team comment that grapefruit is well known to interfere with the metabolism of many drugs via the cytochrome P450 3A4 pathway, the same pathway that is used to metabolize estrogen.
"Since it is well established that estrogen is associated with breast cancer risk, it is plausible that regular intake of grapefruit would increase a woman's risk of breast cancer," they write in British Journal of Cancer.
The team found that half of the studied cohort reported eating grapefruit at some point, with 7% reporting that they ate at least 60 g of grapefruit or more per day.
"Grapefruit intake was significantly associated with an increased risk of breast cancer," state Monroe and team. Indeed, the relative risk was 1.3 for those in the highest intake category of 60 g per day.
Furthermore, the team observed that the risk of breast cancer was increased among women who used estrogen or progestin replacement therapy, and among those who had never received hormone replacement therapy (HRT).
Interestingly, the risk of breast cancer associated with eating grapefruit was higher in women who had never used HRT.
Monroe and colleagues caution that their results need further validation, and as they were unable to assess the additional effect of drinking grapefruit juice, the potential risk could be underestimated.
Last updated 26 July 2007
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