关于维生素是否有必要补充的争论已经很久，从大量的大规模流行病学调查资料发现，补充维生素有可能增加肿瘤的发生，但另一方面，民众对维生素补充的接受度很高，日常补充维生素的比例相当高，特别是经济发达国家的比例更高。今天《自然》介绍一篇最新相关研究，有可能使这一争论火上浇油。研究发现，通过静脉注射维生素C可以提高化疗效果，这和40年前诺贝尔获得者鲍林坚持大量口服维生素C可以抗癌的说法是否一致，新闻中采访了一些专家，有的认为是口服和静脉注射的作用完全不同，静脉注射是促氧化作用，口服是抗氧化作用，而化疗的根本是利用氧化损伤效应杀伤肿瘤细胞，所以静脉注射有辅助效果，如果口服可能有对抗的作用。真是公说公有理。

到底怎么区分正确和错误，请看下文：

Vitamin C injections easeovarian-cancer treatments

High doses reducechemotherapy side effects in humans and fight tumours in mice.

People with ovariancancer who receive high-dose vitamin C injections are less likely to reporttoxic side effects from chemotherapy than people who had chemotherapy alone,according to the results of a small clinical trial.

The study, publishedtoday in Science Translational Medicine1, was too small to assess whether thecombination of chemotherapy and vitamin C combats cancer better thanchemotherapy alone. But accompanying work in mice suggests that the twotreatments could be complementary.  

The results are thelatest salvo in long-running controversy over the use of vitamin C againstcancer. Early studies championed by Nobel-prizewinning chemist Linus Pauling inthe 1970s suggested that vitamin C could help to fight tumours2. But largerclinical trials failed to substantiate those claims3, 4.

As a result, the verytopic of vitamin C in cancer treatment is taboo among many scientists andphysicians, says Melanie McConnell of Victoria University of Wellington in NewZealand, who has studied the effects of high doses of vitamin C on cancer cellsgrown in culture. “When you present this kind of work and you put up the firstslide, everyone snickers,” she says.

Despite such attitudes,people with cancer are flocking to the treatment, says Jeanne Drisko, aphysician who practises integrative medicine at the University of KansasHospital in Kansas City. Drisko and her colleagues, including cancer researcherQi Chen, who is also at the University of Kansas, decided that the purportedeffects of the vitamin warranted a closer look. They noticed that earliertrials had partially relied on intravenous administration of high doses ofvitamin C, or ascorbate, whereas the larger follow-up studies had used onlyoral doses of the drug.

This, they reasoned,could be an important difference: ascorbate is processed by the body indifferent ways when administered orally versus intravenously. Oral doses act asantioxidants, protecting cells from damage caused by reactive compounds thatcontain oxygen. But  vitamin C givenintravenously can have the opposite effect by promoting the formation of one ofthose compounds: hydrogen peroxide. Cancer cells are particularly susceptibleto damage by such reactive oxygen-containing compounds.

Drisko, Chen and theircolleagues found that high concentrations of vitamin C damaged DNA and promotedcell death in ovarian cancer cells grown in culture. In mice grafted with humanovarian cancer cells, treatment with intravenous vitamin C combined withconventional chemotherapy slowed tumour growth, compared to chemotherapytreatment alone.

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The team followed up onthese results with a clinical trial in 25 people with ovarian cancer, 13 ofwhom received both chemotherapy and vitamin C injections. These people wereless likely to report side effects from the chemotherapy treatment than thosewho received chemotherapy alone.

McConnell, who was notinvolved in the study, cautions that the approach might not work for every typeof cancer. She notes that some cancers express low levels of a moleculartransporter that takes up vitamin C, and therefore may not be as susceptible tothe treatment.

But she agrees that it istime to do a larger trial to find out whether the approach is worthwhile,especially because people are already seeking out the treatment. “There’s along way to go before people stop snickering,” she says. “If it works, thengreat. And if it’s doing more harm than good, then that’s something we need toknow, too.”

Nature doi:10.1038/nature.2014.14673