什么是自由基？

自由基是高活性化学物质，有可能伤害细胞。它们是在原子或分子，获得或失去电子时产生的。

自由基是人体自然形成的，并在许多正常细胞过程中发挥重要作用。然而，在高浓度下，自由基可能对身体有害并损害细胞的所有主要成分，包括DNA，蛋白质和细胞膜。

自由基引起的细胞损伤，特别是对DNA的损伤，也可以在癌症和其他健康状况的发展中发挥作用。

暴露于电离辐射和其他环境毒素可导致体内异常高浓度的自由基。当电离辐射撞击细胞中的原子或分子时，电子可能会丢失，从而形成自由基。异常高水平的自由基的产生是电离辐射杀死细胞的机制。

此外，一些环境毒素，如香烟烟雾，某些金属，可能含有大量的自由基或刺激人体细胞产生更多的自由基。

含有元素氧的自由基是活组织中产生的最常见的自由基类型。对于他们的另一名称是“ 活性氧物质 ”。

什么是抗氧化剂？

抗氧化剂是与自由基相互作用并中和自由基的化学物质，从而防止它们造成损害。抗氧化剂也被称为“自由基清除剂”。

身体会产生一些用来中和自由基的抗氧化剂。这些抗氧化剂被称为内源性抗氧化剂，然而，身体依赖外部（外源）来源，主要是饮食，以获得其所需的其他抗氧化剂。这些外源性抗氧化剂通常被称为膳食抗氧化剂。

水果，蔬菜和谷物是膳食抗氧化剂的丰富来源。膳食抗氧化剂包括β-胡萝卜素，番茄红素和维生素A，C和E（α-生育酚）。

抗氧化补充剂帮助预防癌症？

在实验室和动物研究中，已经证明存在增加外源性抗氧化剂可以预防与癌症发展相关的自由基损伤类型。但是在人体体内如何呢？

许多观察性研究，包括病例对照研究和队列研究已经进行，以调查饮食抗氧化剂补充剂的使用是否与降低人类癌症风险相关。总体而言，这些研究得出了不同的结果。由于观察性研究无法充分控制可能影响研究结果的偏倚，因此必须谨慎对待任何个体观察性研究的结果。

迄今为止，已在全世界范围内进行了用于预防癌症的膳食抗氧化剂补充剂的随机对照试验。

总体而言，这9项随机对照临床试验未提供膳食抗氧化剂补充剂对原发性癌症预防有益的证据。

此外，对美国预防服务工作组（USPSTF）进行的有关使用维生素和矿物质补充剂预防慢性病（包括癌症）的现有证据的系统评价同样没有发现预防癌症的明确证据。

患癌症的人该服用抗氧化剂？

一些随机对照试验，已经研究了在癌症治疗期间服用抗氧化剂补充剂是否会改变特定疗法的有效性或降低其毒性。虽然这些试验的结果好坏各半，但有些人发现在癌症治疗期间服用抗氧化剂的人效果更差，特别是如果他们是吸烟者。

在一些临床前研究中，已发现抗氧化剂可促进荷瘤小鼠的肿瘤生长和转移，并提高其能力 流通肿瘤细胞发生转移。在了解更多关于抗氧化剂补充剂对癌症患者的影响之前，应谨慎使用这些补充剂。癌症患者应告知医生他们使用任何膳食补充剂。

其实人体有很强大的自动调节系统，不是说你吃了更多的抗氧化剂，身体自由基就清除的更多，同时我们也没必要清除所有自由基。如果服用可以针对性短期进行干预，但是请找专业的营养医师给您评估。

-参考文献-

文章提供者：营养师-李宗沅

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