A new study suggests that taking vitamin C supplements may not be a good idea for cancer patients. In fact, researchers say, the vitamin may protect tumors from the killing effects of radiation and chemotherapy. I don't argue with anyone who takes vitamin supplementation. But, he says, it does suggest that a biological mechanism exists that could mean megadoses of the supplement would be harmful to certain people.
Researchers do know that vitamin C is an antioxidant.
It is taken up in large quantities by cells and can protect them from certain kinds of damage, called oxidative damage, that has been linked to heart disease and stroke. But radiation and chemotherapy rely on causing oxidative damage to destroy cancerous cells. In their research, Golde and colleagues found that cancer cells take in more vitamin C than normal cells. They do this through a system of transporters on their surfaces that pull large amounts of the vitamin into the cell, where it is stored or used to promote the cell's functions, including tumor growth. Thus, Golde says, high doses of the vitamin could theoretically protect cancer cells from the very therapy meant to kill them.