A preliminary study has shown that large doses of vitamin C may decrease the effectiveness of chemotherapy drugs, bringing new confusion into the debate over whether vitamin C supplements can help or harm cancer patients. In the study, researchers treated cancer cells with very high doses of vitamin C and then tried to kill the cells with various cancer drugs; they found that all the drugs were less effective on the pretreated cancer cells than on cells that had received no vitamin dose.
While the effect was only tested in cancer cells and mice, researchers say further studies should look for a parallel effect in humans. “There’s a possibility that taking supplemental vitamin C could have a detrimental effect on cancer treatment,” said study author Dr. Mark L. Heaney…. However, there’s no indication that smaller doses of vitamin C, such as those found in food and ordinary multivitamins, might be a problem, he said [HealthDay News].
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Injections of high doses of vitamin C slowed the growth of tumors in mice by 50 percent, and also prevented the cancers from metastasizing to other parts of the body. Researchers say the findings form a “firm basis” for trials in humans, with a view to using vitamin C injections alongside conventional drugs, particularly for some of the most lethal tumours, such as pancreatic, ovarian and brain cancer [The Guardian].
But some cancer specialists are sceptical, and fear that desperate patients will be prompted to start taking large doses of the vitamin. That may be dangerous, because antioxidants such as vitamin C could undermine the effectiveness of standard cancer drugs and radiation therapy [New Scientist]. Researchers point out that they were only able to deliver a higher dose of the vitamin through intravenous injection and that patients couldn’t get a similar dose through diet or vitamin supplements, because the digestive system can absorb a limited amount of the vitamin.
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