Jan. 5, 2001 -- Grapefruit juice is supposed to be good for you, but that might not always be the case. Drinking grapefruit juice together with certain medicines can increase blood levels of the drug to harmful levels, according to an editorial in the January issue of the journal Nature Medicine.
"[C]itrus fruits contain many substances other than vitamin C and some of them, such as grapefruit and Seville oranges, can be dangerous if you're taking certain medications," writes J.K. Aronson, of the university department of clinical pharmacology at Radcliffe Infirmary in Oxford, England.
So why is grapefruit getting a bad rap? Grapefruit juice inhibits a chemical in the intestine needed to break down many drugs in the body. The absence of this chemical can lead to higher blood levels. In effect, the drug becomes more potent.
This effect has been observed in nearly all calcium channel blockers, a group of drugs used to control blood pressure. Some of them include Plendil, Procardia, and Nisocor. The effect has also been seen in Sandimmune, a drug that suppresses the immune system and sedatives, such as Xanax and Valium. The editorial also warns about the AIDS drug Invirase.
Other classes of drugs which may potentially interact with grapefruit juice include painkillers, antihistamines, steroids, and drugs for asthma. However, this doesn't mean there's a problem with every drug in these categories -- some interact with grapefruit juice, while others do not.
This means, if you like to eat grapefruit or drink grapefruit juice, talk with your doctor when starting a new medication. And ask your pharmacist about the latest information on food-drug interactions for all the medicines you take.
"Grapefruit does interact with some medications, and anyone who's taking calcium channel blockers or statins [for high cholesterol] needs to talk with their physician or pharmacist about this issue," Bill Stinson, PhD, tells WebMD. "However, there are so many positive constituents in grapefruit ... that consumers shouldn't cut it out of their diets completely." Stinson is scientific research director for the Florida State Department of Citrus.
Aaron Burstein, PharmD, agrees. "This is not a cut-and-dry issue," he says. "It's similar to drug-drug interactions. We often prescribe two medications together even though they interact, because we know we can manage the interaction." Burstein is a pharmacokineticist at the National Institutes of Health Clinical Center's Pharmacy Department, in Bethesda, Md.
Now, he says, doctors and patients need to take possible interactions with grapefruit juice into account, too. "Recently, I spoke to a woman who loves grapefruit juice, and takes Tegretol for a seizure disorder. I didn't tell her to avoid all grapefruit juice. I did say it may be necessary to monitor and adjust her dosage appropriately."
Aronson also warns against megadoses of vitamin C supplements. "[N]o matter how much [vitamin C] you take, all you do is increase the concentrations in your urine and gut, and that can cause adverse effects ... [such as] nausea, abdominal cramps, and diarrhea," he writes.
But Joel Edman, DSc, makes another point. "The studies on vitamin C excretion were done on healthy people, so they may not tell us about the possible benefits of higher doses when someone's ill." Edman is a clinical nutritionist at the Center for Integrative Medicine at Thomas Jefferson University Hospital in Philadelphia.
"In my opinion, an optimal amount [of vitamin C] is between 300 and 1,500 mg per day," he says. "For many people, the lower amount is probably enough, but I want to leave the door open so people who need higher levels due to a current illness, or a family history of illness, will not feel hesitant about taking it."
Everyone should try to follow an optimal diet plus supplements to fit their particular circumstances, Edman says. "Too many people are taking supplements without even knowing why they're taking them." He adds that a diet rich in natural sources of vitamins C and E is an essential foundation for health.
The bottom line? "You can't compensate for a poor diet by taking supplements."