Does Eating Grapefruit Daily Cause Breast Cancer? | Robert A. Erickson, M.D.

From time to time I have patients read something on the Internet about avoiding eating grapefruit with their medications or avoiding this fruit if they or a family member has had breast cancer. The hypothesis is that in some way grapefruit or grapefruit juice will raise estrogen levels in women or in some way interfere with medications. So I did a little research on this topic because at first glance it didn’t make sense to me.

A study was published in the July 2007 edition of The British Journal of Cancer on how daily grapefruit consumption might put women at an increased risk for developing breast cancer. The study was conducted by researchers at UCLA and the University of Hawaii. There appeared to be an “association” between grapefruit consumption and a 30% increased risk of breast cancer development in over 50,000 postmenopausal women studied. This risk did not change whether a woman was taking hormonal replacement therapy or not. This conclusion did not make a lot of sense to me. It also didn’t make sense to other scientists and physicians. I would like to stress an important point to our readers – many times a dramatic headline will appear where one thing is “associated with” something else. There is a big difference between association and causation.

Later that same year another paper was published in the very same medical journal. This study was a prospective study conducted by researchers at Harvard Medical School and affiliated groups using data from the Nurses’ Health Study. The Nurses’ Health Study followed the health and illnesses of 121,700 female registered nurses beginning in 1976 over a 20 year period of time. It assessed risk factors for cancer and cardiovascular disease. This study was among the largest investigations into risk factors for major chronic diseases in women ever conducted. The Harvard study findings were opposite those from the UCLA/Hawaii study and are summarized as follows:

    • Eating grapefruit lowered the overall risk of breast cancer in women not using hormonal replacement (meaning the use of artificial hormones) by roughly 22%

    • Certain forms of breast cancer (ER and PR negative cancers, which can be more aggressive) showed a 40% lower risk of development among grapefruit consumers.

    • There was no correlation between eating grapefruit or drinking grapefruit juice and higher levels of estrogen.

“Our findings do not support an adverse effect of consumption of grapefruit or grapefruit juice on risk of breast cancer or on endogenous hormone levels.”

Going back to the European Prospective Investigation into Cancer and Nutrition (EPIC) study published in 2009, in this study information on usual individual dietary intake was assessed using different validated dietary assessment methods across participating countries. On average, the participants were followed for 9 ½ years. Almost 60% of the women ate some grapefruit on a daily basis. The researchers found no connection between any level of grapefruit consumption and breast cancer risk or elevated hormones.

Now what about the precaution of not taking medications with grapefruit juice? Grapefruit has naturally occurring phytochemicals called furanocoumarins. These phytochemicals can inhibit an enzyme known as CYP3A4. This enzyme can affect the way the liver clears and detoxifies certain medications. Many cardiac medications such as calcium channel blockers and anti-arrhythmic drugs can be affected. Statin drugs can be affected as can some antibiotics and many chemotherapy agents used in cancer treatment. Xanax and other anti-anxiety agents as well as some anti-depressants may also be affected. There are too many drugs to list in this article. These phytochemicals can delay the detoxification of medications through liver metabolism, leading to an increased blood level of the drug. My recommendation is to check with your pharmacist for any potential interactions before mixing the prescription medications you are taking with grapefruit or grapefruit juice.