Reactive oxygen species (ROS), such as hydrogen peroxide, superoxide, hydroxyl radicals, peroxynitrite, singlet oxygen, alkoxyl, and peroxyl radicals, are formed in living cells as part of metabolic processes, such as electron transport systems, and as cell signaling molecules but can also be produced as a response to external stimuli, for example, irradiation, stress, and pollution. ROS are strong oxidants, which are able to modify cell constituents, including DNA, lipids, and proteins. In general, the living cell is able to deal with ROS using complex enzymatic and antioxidant defense and repair systems in order to control ROS and repair the damage caused by ROS. During aging, the metabolism is impaired, and enzymatic systems are less potent resulting in more ROS and in accumulation of oxidized DNA, lipids, and proteins, and this has been shown to result in the pathology of several diseases (Halliwell and Gutteridge 2007; Davies and Dean 2003).