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."