And the effect can last as long as 24 hours, meaning that drinking grapefruit juice at any time is contraindicated when taking drugs metabolized by CYP3A4. Various oral medications, ranging from heart-rhythm regulators and immunosuppressants to estrogen supplements and AIDS treatments, all interact with grapefruit juice. Since CYP3A4 is known to be involved in the metabolism of numerous drugs, researchers suspected that felodipine would not be the sole medication to show a “grapefruit effect.” Indeed it was not. If its action is impaired, blood levels of these foreign substances can be expected to rise. This enzyme is part of the body’s detoxicating system and tackles intruders, such as medications. Some compound specific to grapefruit inhibited the action of CYP3A4, an enzyme found in the wall of the intestine. It wasn’t long before studies showed that only grapefruit juice had this unusual effect. Predictably, The Lancet paper unleashed a cavalcade of research. By what mechanism was grapefruit juice increasing the drug’s effectiveness? Did other juices have such an effect? What about interactions with other drugs? What would happen if the juice were consumed not with the drug but at some other time during the day? Was there a silver lining to this cloud? Could dosages of medications be reduced if they were taken with grapefruit juice? Clearly, when taken with grapefruit juice, felodipine lowered blood pressure more than expected. He didn’t have to wait for the results to confirm the “grapefruit effect.” After taking the medication with grapefruit juice, he began to feel faint and lightheaded, classic symptoms of low blood pressure. One day he took felodipine with water, the next day with grapefruit juice each time he drew blood, and sent it for analysis of drug levels. After all, he had been the first Canadian to run a sub-four-minute mile!Īt this point, the eager scientist decided to become his own guinea pig. To the researchers’ surprise, the alcohol had no effect, but in both groups the blood levels of felodipine were three times higher than expected. ![]() Bailey concluded that grapefruit juice was up to the task. This meant that the taste of alcohol had to be masked, and after some experimentation Dr. ![]() They decided on a double-blind trial in which some subjects were to take the drug with alcohol and some without. David Bailey and colleagues at the University of Western Ontario had been studying felodipine, a blood pressure–lowering drug, and wondered if it interacted with alcohol. “A chance finding of our study on ethanol-drug interactions was that citrus fruit juices may greatly augment the bioavailability of some drugs.” So began a paper published in 1991 in The Lancet, one of the most respected medical journals in the world. All rights reserved.As you might expect, the situation is more complicated than it first seems. However, the improvements in blood pressure and lipids demonstrated in the intervention group suggest that grapefruit should be further evaluated in the context of obesity and cardiovascular disease prevention.Ĭopyright © 2012 Elsevier Inc. This study suggests that consumption of grapefruit daily for 6 weeks does not significantly decrease body weight, lipids, or blood pressure as compared with the control condition. 001), respectively, compared with baseline values. ![]() Improvements were observed in circulating lipids of those consuming grapefruit, with total cholesterol and low-density lipoprotein significantly decreasing by -11.7 mg/dL (P =. 0002), and a significant reduction in systolic blood pressure (-3.21 ± 10.13 mm Hg, P =. ![]() 097), a significant reduction in waist circumference (-2.45 ± 0.60 cm, P =. Grapefruit consumption was associated with modest weight loss (-0.61 ± 2.23 kg, P =. No differences between group in weight, blood pressure, or lipids were demonstrated. Following a 3-week washout diet low in bioactive-rich fruits and vegetables, participants were randomized to either the control diet (n = 32) or daily grapefruit (n = 42) in the amount of one half of a fresh Rio-Red grapefruit with each meal (3× daily) for 6 weeks. The aim of this randomized controlled trial was to prospectively evaluate the role of grapefruit in reducing body weight and blood pressure and in promoting improvements in the lipid profile in overweight adults (N = 74). Sparse data exist to support this hypothesis, although there is some evidence of health promotion effects with regard to blood pressure control and modulation of circulating lipids. Folklore has suggested that consuming grapefruit may promote weight control.
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