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癌症病患与癌症长期存活者普遍使用维他命与矿物质补充品，且高于一般大众；然而，很少有病患会与他们的医师讨论饮食补充品，且医师经常没有询问相关问题。
研究者在2月1日的临床肿瘤学期刊上表示，不幸的，这些产品对于癌症本身与使用于治疗癌症的药物是有不良影响的；资深作者华盛顿西雅图佛雷德哈钦森癌症中心的Cornelia Ulrich博士表示，证据显示这需要注意。某些维他命，例如叶酸，可能与癌症进展有关，然而，其他的饮食补充品，例如圣约翰草，会干扰化学治疗疗效。使用这些补充品是否有益、或是害多于益，我们确实需要更多的研究。
Ulrich博士呼吁健康照护者应该与癌症病患与存活者讨论这些议题，她在一项声明中表示，医学研究结果显示使用补充品并不总是有益，可帮助癌症存活者做出被充分告知的决定。
作者进行一项系统性回顾，总共收纳32项研究，这些研究发表于1999年与2006年之间，总共收纳了超过15,000位病患，整体而言，64%至81%癌症与存活病患有使用任何维他命或是矿物质补充品；使用任何复合维他命的比例从26%到77%。
研究者评论，这样的比例比报导中美国一般大众的高；研究者表示，介于25%到33%的一般大众使用复方维他命或矿物质补充品，且超过50%的一般大众使用饮食补充品。
文章中有三篇研究针对诊断罹癌后使用饮食补充品的变化，三项研究结果皆显示诊断罹癌后使用补充品的情况增加；研究者也研究不同种类的癌症，发现乳癌患者使用复方维他命的比例最高，介于57%与62%；摄护腺癌患者使用的比例最低，仅有3%到23%。
研究者写道，整体来看，癌症存活者似乎相信饮食补充品是有益的；过去一项研究结果显示，病患表示使用这些补充品的原因是希望强化他们的免疫系统、帮助他们对抗压力、增加他们被治愈的机会、取得控制的感觉、或是协助他们感觉好一点；然而，他们写道，医师可以建议透过其他方式来达到这些目标；举例来说，如果病患正在服用补充品希望对抗压力，医师可以引介病患接受其他形式的治疗（例如瑜珈、支持团体）。
研究者提到，某些流行病学研究数据显示，癌症病患使用饮食补充品是有好处的；举例来说，一项针对非小细胞肺癌患者的研究显示，使用维他命与矿物质的患者，相较于没有使用这些补充品的患者，其存活率改善了35%（Lung Cancer 2005;49:77-84）。
然而，他们指出，也有数据显示这是有害的；一项大肠直肠息肉的化学预防随机分派研究结果显示，叶酸确实会加速癌前大肠病灶的进展（JAMA 2007;297:2351-2359），且一项针对头颈部癌症的随机分派研究结果显示，在放射线治疗时或是之后使用维生素E，在前3.5年的后续追踪中与较高的再发率与继发性癌症机率增加有关（J Natl Cancer Inst 2005;97:481-488）。除此之外，圣约翰草，具有抗忧郁效果的草药，对于牵涉到药物代谢的细胞色素P450系统有众所皆知的影响，且已经被证实会降低irinotecan活性代谢物的浓度。
作者的结论是，需要未来更多的研究来确认这项议题，且在这之前医师与癌症病患需要了解与讨论与使用饮食补充品相关的问题。
作者表示无相关资金上的往来。
Vitamin and Mineral Use Widespread Among Cancer Patients
By Zosia Chustecka
Medscape Medical News
Vitamin and mineral use is widespread among cancer patients and long-term cancer survivors, and frequently higher than among the general population. However, few patients discuss dietary supplements with their physicians, and doctors often do not ask about them. Unfortunately, these products can have an adverse effect on the cancer itself or on the drugs being used to treat it, researchers point out in the February 1 issue of the Journal of Clinical Oncology.
"Evidence clearly suggests the need for caution," said senior author Cornelia Ulrich, PhD, from Fred Hutchinson Cancer Research Center in Seattle, Washington. "Some vitamins, such as folic acid, may be involved in cancer progression, whereas others, such as St. John's wort, can interfere with chemotherapy. However, we really need more research to understand whether use of these supplements can be beneficial or do more harm than good."
Dr. Ulrich urges health professionals to communicate these concerns to cancer patients and survivors. "A simple explanation that medical studies show supplement use may not always be beneficial can help cancer survivors make well-informed decisions," she said in a statement.
The authors carried out a systematic review of 32 studies, published between 1999 and 2006, that involved more than 15,000 patients. Overall, the use of any vitamin or mineral was reported by 64% to 81% of cancer patients and survivors; the use of any multivitamins ranged from 26% to 77%.
This is higher than the use reported by the general population in the United States, the researchers comment. Between 25% and 33% of the general population use multivitamin/multimineral supplements, and more than 50% use dietary supplements, the researchers comment.
Three of the studies in the review looked at changes in supplement use after cancer was diagnosed, and all 3 showed an increase after diagnosis. The researchers also considered different types of cancer, and found that breast cancer patients had the highest use of multivitamins, between 57% and 62%; use by prostate cancer patients was between 3% and 23%.
Cancer survivors overall seem to believe that dietary supplements are beneficial, the researchers write. A previous study reported patients saying that they took them to strengthen their immune system, help them cope with stress, enhance their chance of a cure, gain a sense of control, or help them to feel better. However, physicians can suggest other ways of achieving these goals, they write. "For example, if the patient is taking take supplements to help cope with stress, physicians can direct patients to other means (eg, yoga, support groups)."
Some epidemiologic evidence suggests that there are benefits from supplement use among cancer patients, the researchers note. For instance, a study in nonsmall-cell lung cancer showed a 35% improvement in survival among patients who used vitamins and minerals, compared with those who didn't (Lung Cancer 2005;49:77-84).
However, there are also data suggesting harm, they point out. A randomized study of chemoprevention for colorectal polyps suggested that folic acid actually fosters progression of premalignant colonic lesions (JAMA 2007;297:2351-2359), and a randomized trial of head and neck cancer found that supplementation with alpha-tocopherol during and after radiation was associated with a higher incidence of recurrence and second primary cancers in the first 3.5 years of follow-up (J Natl Cancer Inst 2005;97:481-488). In addition, St. John's wort, the herbal antidepressant, has a well-documented effect on the cytochrome P450 system involved in drug metabolism, and has been shown to lower plasma levels of the active metabolite of irinotecan.
Further research is needed to clarify the issue, and until then both physicians and cancer patients "need to understand and discuss the potential concerns associated with dietary supplement use," the authors conclude.
The authors have disclosed no relevant financial relationships.
J Clin Oncol. 2008; 26:665-673. Abstract