氧化是一種使電子自物質轉移至氧化劑的化學反應，過程中可生成自由基，進而啟動鏈反應。當鏈反應發生在細胞中，細胞受到破壞或凋亡。抗氧化劑則能去除自由基，終止連鎖反應並且抑制其它氧化反應，同時其本身被氧化。 雖然氧化反應十分重要，但它也能對生命體造成傷害；因此，動植物演化出多種抗氧化劑，如常見的穀胱甘肽、維生素C與維生素E，過氧化氫酶、超氧化物歧化酶等酶，以及各種過氧化酶。低階的抗氧化劑或抗氧化酶的抑制劑，則會引發氧化應激，導致細胞的損傷和死亡。 抗氧化劑被廣泛應用在營養補充劑中。對於一些疾病比如癌症、冠心病甚至高原反應的預防作用已經得到研究。

Oxidation is a chemical reaction that can produce free radicals, thereby leading to chain reactions that may damage the cells of organisms. Antioxidants such as thiols or ascorbic acid (vitamin C) terminate these chain reactions. To balance the oxidative stress, plants and animals maintain complex systems of overlapping antioxidants, such as glutathione and enzymes (e.g., catalase and superoxide dismutase), produced internally, or the dietary antioxidants vitamin C, and vitamin E. The term "antioxidant" is mostly used for two entirely different groups of substances: industrial chemicals that are added to products to prevent oxidation, and naturally occurring compounds that are present in foods and tissue. The former, industrial antioxidants, have diverse uses: acting as preservatives in food and cosmetics, and being oxidation-inhibitors in fuels. Antioxidant dietary supplements have not been shown to improve health in humans, or to be effective at preventing disease. Supplements of beta-carotene, vitamin A, and vitamin E have no positive effect on mortality rate or cancer risk. Additionally, supplementation with selenium or vitamin E do not reduce the risk of cardiovascular disease.

天然物、抗氧化劑

Nature, Antioxidant