Greenberg E R, Baron J A, Tosteson T D, Freeman D H, Beck G J, Bond J H, Colacchio T A, Coller J A, Frankl H D, Haile R W
Dartmouth-Hitchcock Medical Center, Lebanon, N.H.
N Engl J Med. 1994 Jul 21;331(3):141-7. doi: 10.1056/NEJM199407213310301.
People who consume a diet high in vegetables and fruits have a lower risk of cancer of the large bowel. Antioxidant vitamins, which are present in vegetables and fruits, have been associated with a diminished risk of cancers at various anatomical sites. We conducted a randomized, controlled clinical trial to test the efficacy of beta carotene and vitamins C and E in preventing colorectal adenoma, a precursor of invasive cancer.
We randomly assigned 864 patients, using a two-by-two factorial design, to four treatment groups, which received placebo; beta carotene (25 mg daily); vitamin C (1 g daily) and vitamin E (400 mg daily); or the beta carotene plus vitamins C and E. In order to identify new adenomas, we performed complete colonoscopic examinations in the patients one year and four years after they entered the study. The primary end points for analyses were new adenomas identified after the first of these two follow-up examinations.
Patients adhered well to the prescribed regimen, and 751 completed the four-year clinical trial. There was no evidence that either beta carotene or vitamins C and E reduced the incidence of adenomas; the relative risk for beta carotene was 1.01 (95 percent confidence interval, 0.85 to 1.20); for vitamins C and E, it was 1.08 (95 percent confidence interval, 0.91 to 1.29). Neither treatment appeared to be effective in any subgroup of patients or in the prevention of any subtype of polyp defined by size or location.
The lack of efficacy of these vitamins argues against the use of supplemental beta carotene and vitamins C and E to prevent colorectal cancer. Although our data do not prove definitively that these antioxidants have no anticancer effect, other dietary factors may make more important contributions to the reduction in the risk of cancer associated with a diet high in vegetables and fruits.
食用富含蔬菜和水果的饮食的人群患大肠癌的风险较低。蔬菜和水果中所含的抗氧化维生素与降低不同解剖部位癌症的风险有关。我们进行了一项随机对照临床试验，以测试β-胡萝卜素、维生素C和维生素E预防结直肠腺瘤（浸润性癌的前体）的疗效。
我们采用二乘二析因设计将864例患者随机分为四个治疗组，分别接受安慰剂；β-胡萝卜素（每日25毫克）；维生素C（每日1克）和维生素E（每日400毫克）；或β-胡萝卜素加维生素C和维生素E。为了识别新的腺瘤，我们在患者进入研究一年和四年后对其进行了全结肠镜检查。分析的主要终点是这两次随访检查中首次检查后发现的新腺瘤。
患者对规定方案的依从性良好，751例完成了四年的临床试验。没有证据表明β-胡萝卜素或维生素C和E能降低腺瘤的发生率；β-胡萝卜素的相对风险为1.01（95%置信区间，0.85至1.20）；维生素C和E的相对风险为1.08（95%置信区间，0.91至1.29）。两种治疗方法在任何患者亚组中或预防任何由大小或位置定义的息肉亚型方面似乎都无效。
这些维生素缺乏疗效，反对使用补充β-胡萝卜素、维生素C和维生素E来预防结直肠癌。虽然我们的数据不能明确证明这些抗氧化剂没有抗癌作用，但其他饮食因素可能对降低与富含蔬菜和水果的饮食相关的癌症风险做出更重要的贡献。
