Several different reactive oxygen species (ROS) are generated in vivo. They have roles in the development of certain human diseases whilst also performing physiological functions. ROS are counterbalanced by an antioxidant defence network, which functions to modulate ROS levels to allow their physiological roles whilst minimizing the oxidative damage they cause that can contribute to disease development. This Review describes the mechanisms of action of antioxidants synthesized in vivo, antioxidants derived from the human diet and synthetic antioxidants developed as therapeutic agents, with a focus on the gaps in our current knowledge and the approaches needed to close them. The Review also explores the reasons behind the successes and failures of antioxidants in treating or preventing human disease. Antioxidants may have special roles in the gastrointestinal tract, and many lifestyle features known to promote health (especially diet, exercise and the control of blood glucose and cholesterol levels) may be acting, at least in part, by antioxidant mechanisms. Certain reactive sulfur species may be important antioxidants but more accurate determinations of their concentrations in vivo are needed to help assess their contributions.

体内会产生几种不同的活性氧（ROS）。它们在某些人类疾病的发展中发挥作用，同时也发挥生理功能。ROS 通过抗氧化防御网络来平衡，该网络的功能是调节 ROS 水平，以发挥其生理作用，同时最大限度地减少它们引起的氧化损伤，从而导致疾病的发展。本综述描述了体内合成的抗氧化剂、源自人类饮食的抗氧化剂以及作为治疗剂开发的合成抗氧化剂的作用机制，重点关注我们当前知识的差距以及弥补这些差距所需的方法。该评论还探讨了抗氧化剂在治疗或预防人类疾病方面成功和失败背后的原因。抗氧化剂可能在胃肠道中发挥特殊作用，许多已知可促进健康的生活方式特征（特别是饮食、锻炼以及控制血糖和胆固醇水平）可能至少部分通过抗氧化机制发挥作用。某些活性硫物质可能是重要的抗氧化剂，但需要更准确地测定其体内浓度以帮助评估其贡献。