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].
In the study, published in Cancer Research [subscription required], researchers also treated cancerous mice with a megadose of vitamin C equivalent to 2,000-milligram dose for humans; that’s the amount found in 75 six-ounce glasses of orange juice, but such doses are often found in vitamin supplements. The tumors in the treated mice grew rapidly despite chemotherapy, while the cancer drugs kept the tumors in check in untreated mice.
Scientists have previously wondered whether vitamin C might protect cancer cells because of its anti-oxidant properties; the theory was that since some chemotherapy drugs produce free radicals in the cancer cells to kill them, vitamin C might be inadvertently protecting the cells by mopping up those free radicals. But the researchers in the current study suggest a different mechanism: Instead, vitamin C appeared to protect tiny structures inside the cancer cells called mitochondria from damage. Mitochondria effectively form the energy-creating boiler room of a cell, and if damaged can lead to its death…. Heaney said: “Vitamin C appears to protect the mitochondria from extensive damage, thus saving the cell. “And whether directly or not, all anti-cancer drugs work to disrupt the mitochondria to push cell death” [BBC News].
The new study is the latest twist in the controversy over vitamin C; just two months ago, a different research team found that vitamin C injections shrunk tumors in mice.
Could Vitamin C Injections Slow Cancer Growth?