Many people gobble big doses of vitamin C in hopes of boosting their immune system and warding off illness. But new research shows that in people with cancer, the vitamin may do more harm than good.

Researchers at Memorial Sloan-Kettering Cancer Center in New York studied the effects of vitamin C on cancer cells. As it turns out, the vitamin seems to protect not just healthy cells, but cancer cells, too. The findings were published today in the journal Cancer Research.

“The use of vitamin C supplements could have the potential to reduce the ability of patients to respond to therapy,” said Dr. Mark Heaney, an associate attending physician at the cancer center.

Dr. Heaney and his colleagues tested five different chemotherapy drugs on cancer cells in the laboratory. Some of the cells were first treated with vitamin C. In every case, including a test of the powerful new cancer drug Gleevec, chemotherapy did not work as well if cells had been exposed to vitamin C. The chemotherapy agents killed 30 to 70 percent fewer cancer cells when the cells were treated with the vitamin.

A second set of experiments implanted cancer cells in mice. They found that the tumors grew more rapidly in mice that were given cancer cells pretreated with vitamin C.

The researchers found that just like healthy cells, cancer cells also benefit from vitamin C. The vitamin appeared to repair a cancer cell’s damaged mitochondria, the energy center of cells. When the mitochondria is injured, it sends signals that force the cell to die, but vitamin C interrupts that process.

“Vitamin C appears to protect the mitochondria from extensive damage, thus saving the cell,” Dr. Heaney said. “And whether directly or not, all anticancer drugs work to disrupt the mitochondria to push cell death.”

Dr. Heaney measured the buildup of vitamin C levels in cells and said that the levels of vitamin C used in the experiments were similar to those that would result if a patient took large doses of the vitamin in supplement form. Earlier research at the cancer center showed that vitamin C seems to accumulate within cancer cells more than in normal cells.

Patients should eat a healthy diet that includes foods rich in vitamin C, Dr. Heaney said, but it’s the large doses of vitamin C in tablet form that are

许多人大量吞食维C，希望提高免疫系统功能，防止疾病。但新研究表明，对患有癌症的人们来说，维生素可能害弊大于利。

纽约斯隆凯特灵纪念癌症中心的研究员们研究了维C对癌细胞的影响。结果是，维生素似乎不仅仅保护了健康细胞，也会保护癌细胞。发现今天发表在《癌症研究》杂志上。

“使用维C补充剂可能降低病人对治疗的反应能力”，癌症中心副主任医生Mark Heaney博士说。

Heaney博士和他的同事们在实验室里测试了五种不同的治疗癌细胞的化学药物。有些细胞先用维生素C进行处理。在每种情况下，包括强效新癌药Gleevec的测试，化学疗法效果都不是很好，如果癌细胞事先接触维生素C。当癌细胞事先用维生素处理的话，化学药剂杀死癌细胞数量会减少30－70％。

第二组试验是将癌细胞注入白鼠。他们发现，如果癌细胞事先用维生素C处理过，肿瘤在白鼠体内生长更快。

研究员们发生正如正常细胞一样，癌细胞也得益于维生素C。维C好象可以修复癌细胞中破坏的线粒体，这是细胞的能量中心。当线粒体被破坏时，它发出信号迫使细胞死亡，但维C中断了这个过程。

“维C好象可以保护线粒体免受很多重大损害，因此挽救细胞”，Heaney博士说。“不管直接与否，所有的抗癌药都可以中断线粒体让细胞死亡”。

Heaney博士检测了细胞中维C水平的组成，并称实验中所用的维C含量水平与那种结果一样，如果病人大量食用大剂量的补充剂。癌症中心早期研究表明，癌细胞内维C累积量似乎可以比正常细胞内的堆积量更高。

病人应该食用正常膳食，包括富含维C的食物，Heaney博士说，但药片维C的大剂量令人担忧。