Antioxidants

Abstract In the human body, antioxidant functions (elimination of excessive reactive oxygen species (ROS)) are primarily exerted by enzyme systems in cells and tissues or by antioxidant molecules produced by metabolism. A large number of molecules, chemically defined as antioxidants, present in fruits and vegetables (polyphenols, tocopherols and carotenoids) are provided with the property of delaying or inhibiting oxidations. They can exhibit additional functions such as of ligands to macromolecules (receptors, enzymes, etc.). The in vitro properties of antioxidants may not be present in vivo , if the antioxidant is not absorbed, or if it is modified, if it is inactivated or rapidly eliminated. Antioxidants may scavenge ROS in excess that can damage cell components, such as deoxyribonucleic acid , proteins, lipids and low‐molecular weight compounds. However, because ROS represent physiological components of cell metabolism and are used for cell signalling, antioxidants may interfere with physiological cell signalling. Although epidemiological studies have suggested a positive health impact of antioxidants present in fruits and vegetables, human interventions with antioxidants have not given till now encouraging results. Key Concepts: Antioxidants are a broad, heterogeneous group of chemicals provided with the property delaying or inhibiting oxidations. Antioxidant functions are also exerted by enzyme systems, physiologically present in cells and tissues. Antioxidants may possess properties additional to their redox reactivity. A clear distinction should be made between in vitro and in vivo properties of antioxidants, because in vivo chemical antioxidants may be inactivated, modified or exhibit different, additional properties. Reactive oxygen species are present as physiological components of cell metabolism and are used for cell signalling. Reactive oxygen species in excess can damage cell components, such as DNA, proteins, lipids and low‐molecular weight compounds, and be the cause of disease. Antioxidants may on one side prevent the damage produced by excess oxidants, but they may also interfere with the physiological signalling produced by reactive oxygen species. Epidemiological studies have suggested a positive health impact of antioxidants present in fruits and vegetables. Human interventions with antioxidants have not given till now encouraging results.