Oxidative stress is the imbalance between oxidants and antioxidants in favor of the oxidants which are formed as a normal product of aerobic metabolism but during pathophysiological conditions can be produced at an elevated rate.
Both enzymatic and nonenzymatic strategies are involved in antioxidant defense, and antioxidant efficacy of any molecule depends on the co-oxidant. Well proven free radical scavengers can be prooxidant unless linked to a radical sink. Moreover, as the free radicals share a physiological as well as a pathological role in the body, the same antioxidant molecule just due to its free radical scavenging activity may act as disease promoter, by neutralizing the physiologically desired ROS molecules, and as disease alleviator by removing the excessive levels of ROS species.
The importance of several vitamins like vitamin A and tocopherols as well as carotenes, oxycarotenoids, and ubiquinols in their lipid phase has been understood in recent years. Low molecular mass antioxidant molecules that include nuclear as well as mitochondrial matrices, extracellular fluids, have been studied to understand how they accelerate the body defense.