Reactive species and antioxidants. Redox biology is a fundamental theme of aerobic life

ROS are all over the place in plants, animals, and aerobic bacteria. We cannot live without them or we will probably die from infections. Yet, they often kill us in the end; over the long human lifespan, the continual damage by ROS, if not properly repaired (and repair efficiency tends to drop in the aged) can contribute to the age-related development of cancer, neurodegenerative diseases, and many other disorders (Ames, 1983; Halliwell and Gutteridge, 2006). This may be a by product of evolution; ROS are essential for defense against infection and signaling, keeping you alive until your reproduction has finished and children have grown up. Who cares if they kill you in the later post-reproductive years? Evolution doesn't. So why does taking antioxidant supplements not make us live healthily for ever? Simply because the human body regulates the ROS/antioxidant balance so carefully that feeding antioxidants does not disturb it much, and oxidative damage does not decrease (Halliwell, 1999, 2000). © 2006 American Society of Plant Biologists.