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

許多人大量吞食維C，希望提高免疫系統功能，防止疾病。但新研究表明，對患有癌癥的人們來說，維生素可能害弊大于利。

紐約斯隆凱特靈紀念癌癥中心的研究員們研究了維C對癌細胞的影響。結果是，維生素似乎不僅僅保護了健康細胞，也會保護癌細胞。發現今天發表在《癌癥研究》雜志上。

“使用維C補充劑可能降低病人對治療的反應能力”，癌癥中心副主任醫生Mark Heaney博士說。

Heaney博士和他的同事們在實驗室里測試了五種不同的治療癌細胞的化學藥物。有些細胞先用維生素C進行處理。在每種情況下，包括強效新癌藥Gleevec的測試，化學療法效果都不是很好，如果癌細胞事先接觸維生素C。當癌細胞事先用維生素處理的話，化學藥劑殺死癌細胞數量會減少30－70％。

第二組試驗是將癌細胞注入白鼠。他們發現，如果癌細胞事先用維生素C處理過，腫瘤在白鼠體內生長更快。

研究員們發生正如正常細胞一樣，癌細胞也得益于維生素C。維C好象可以修復癌細胞中破壞的線粒體，這是細胞的能量中心。當線粒體被破壞時，它發出信號迫使細胞死亡，但維C中斷了這個過程。

“維C好象可以保護線粒體免受很多重大損害，因此挽救細胞”，Heaney博士說。“不管直接與否，所有的抗癌藥都可以中斷線粒體讓細胞死亡”。

Heaney博士檢測了細胞中維C水平的組成，并稱實驗中所用的維C含量水平與那種結果一樣，如果病人大量食用大劑量的補充劑。癌癥中心早期研究表明，癌細胞內維C累積量似乎可以比正常細胞內的堆積量更高。

病人應該食用正常膳食，包括富含維C的食物，Heaney博士說，但藥片維C的大劑量令人擔憂。