Hennekens C H
Department of Medicine and Ambulatory Care and Prevention, Harvard Medical School, Boston, Massachusetts.
Am J Med. 1994 Sep 26;97(3A):2S-4S; discussion 22S-28S. doi: 10.1016/0002-9343(94)90291-7.
Cancer is the second leading cause of death in the United States as well as most developed countries. Although advances in treatment have afforded tremendous benefits to large numbers of patients, effective primary prevention measures could, in theory, have an even greater public health impact. Diet has been postulated to account for as much as 35% of all human cancers, raising the possibility that specific constituents of diet with cancer chemopreventive effects could be identified. Risk reductions of even 20-30%, which is the most likely magnitude of any protective effect of nutritional agents, could have a significant public health impact on so common and serious a disease. Antioxidant vitamins are among the constituents of diet hypothesized to exert chemopreventive effects. Antioxidant vitamins, which include beta-carotene (pro-vitamin A), vitamin E, and vitamin C, are hypothesized to decrease cancer risk by preventing tissue damage by trapping organic free radicals and/or deactivating excited oxygen molecules, a by-product of many metabolic functions. Over 100 observational epidemiologic studies have assessed the relationship of dietary antioxidant intake or blood nutrient levels with cancer risk. Such studies are not entirely consistent but provide support for the hypothesis that antioxidant vitamin intake may decrease cancer risk. However, the chief limitation of such observational studies is their inability to control for all factors associated with vitamin intake that might independently affect cancer risk. Such unknown or unmeasured confounding variables could account for all or part of any observed associations. For this reason, definitive data on the role of antioxidant vitamins and cancer can derive only from properly conducted large-scale randomized trials of sufficient sample size, dose, and duration of treatment and follow-up. Two large-scale trials have been completed, and several are currently ongoing among well-nourished populations at high risk for cancer as well as among individuals at usual risk. Over the next several years, these trials should provide clear evidence concerning the role of antioxidant vitamins in the prevention of cancer. Such data are crucial for both individual clinical decision making as well as rational public health policy.
癌症是美国以及大多数发达国家的第二大死因。尽管治疗方面的进展已使大量患者受益匪浅，但理论上有效的一级预防措施可能对公众健康产生更大影响。据推测，饮食因素在所有人类癌症中所占比例高达35%，这增加了识别具有癌症化学预防作用的特定饮食成分的可能性。即使营养剂的保护作用最有可能达到20%-30%的风险降低幅度，也会对这种常见且严重的疾病产生重大的公共卫生影响。抗氧化维生素是饮食中被假定具有化学预防作用的成分之一。抗氧化维生素包括β-胡萝卜素（维生素A原）、维生素E和维生素C，据推测它们可通过捕获有机自由基和/或使许多代谢功能的副产品——激发态氧分子失活来防止组织损伤，从而降低癌症风险。超过100项观察性流行病学研究评估了饮食中抗氧化剂摄入量或血液营养水平与癌症风险之间的关系。这些研究并不完全一致，但为抗氧化维生素摄入可能降低癌症风险这一假设提供了支持。然而，此类观察性研究的主要局限性在于它们无法控制所有与维生素摄入相关的、可能独立影响癌症风险的因素。此类未知或未测量的混杂变量可能解释了所有或部分观察到的关联。因此，关于抗氧化维生素与癌症作用的确切数据只能来自适当开展的、具有足够样本量、剂量、治疗持续时间和随访时间的大规模随机试验。两项大规模试验已经完成，目前还有几项试验正在营养良好的癌症高危人群以及一般风险个体中进行。在未来几年里，这些试验应能提供关于抗氧化维生素在癌症预防中作用的明确证据。此类数据对于个体临床决策以及合理的公共卫生政策都至关重要。
