Grapefruit has been found to have antioxidant, antiseptic, detoxicant, antinitrosaminic, cardiotonic, hypocholesterolemic, and sedative actions. Although components of grapefruit peel have been found to reduce blood pressure by decreasing coronary vascular resistance and mean arterial pressure, pink grapefruit juice appears to have proarrhythmic actions which might be of concern for some heart patients. One major 2015 study reported that people with diets high in grapefruit (but not grapefruit juice) may be at modestly increased risk for malignant melanoma, possibly from ingesting photosensitizing compounds called psoralens found in citrus fruits.
Pink grapefruit is a good source of vitamin C, as well as the phytochemicals naringenin, limonene, beta-carotene and lycopene, and also contains hesperidin. Naringenin has been shown to have cytotoxic activity against leukemia, stomach, colon, liver, pancreas, cervix, and breast cancer cells. D-limonene has been used clinically to dissolve cholesterol-containing gallstones and for the relief of heartburn and gastroesophageal reflux disease. In addition, D-limonene has been shown to inhibit the proliferation of human colon cancer cells. Lycopene, a cartenoid responsible for the red color in pink and red grapefruit, has been found to inhibit the proliferation of rat prostate cancer cells in a dose-dependent manner.
Breast cancer-related effects of eating grapefruit
Various grapefruit phytochemicals have been shown to have chemopreventive effects with respect to breast cancer. For example, naringenin has been shown to inhibit the proliferation of hormone receptor positive MCF-7 breast cancer cells by impairing glucose uptake. A major epidemiological study published in 2009 found no evidence of an association between grapefruit intake and the risk of breast cancer.
However, there is evidence to suggest that grapefruit may play a role in estrogen metabolism (in much the same way that drug interactions occur with grapefruit), thereby increasing circulating estrogen and breast cancer risk. Another major population study published in 2007 found that grapefruit consumption was associated with increased risk of breast cancer among postmenopausal women. Still another 2007 study of postmenopausal Mexican-American women found that consumption of grapefruit was associated with higher circulating estrogen levels. A While the results of both population-based and laboratory studies concerning grapefruit are contradictory, there is enough evidence to suggest grapefruit consumption should be limited or avoided by breast cancer patients and survivors, especially those with ER+ disease.
Grapefruit should not be consumed during chemotherapy, endocrine treatment, or Herceptin treatment. Grapefruit juice can affect the metabolism of many drugs, in some cases increasing their effect and in other cases blocking their intended action. The effect can vary considerably from person to person, so that the extent of the impact of consuming grapefruit juice on drug metabolism is not predictable. Drug interactions have been observed between grapefruit and albendazole, amiodarone, atorvastatin, buspirone, carbamazepine, cisapride, cyclosporine, diltiazem, etoposide, felodipine, lovastatin, midazolam, nitrendipine, nimodipine, nisoldipine, quinidine, sertraline, simvastatin, terfenidine, and triazolam, to name only some of the drugs affected. It has not been clearly determined which components of grapefruit are responsible for these drug interactions.
Below are links to recent studies concerning this food. For a more complete list of studies, please click on grapefruit.