The human body is under constant attack by free radicals (reactive oxygen species – ROS). Free radicals are highly reactive molecules generated by biochemical redox reactions which occur as a part of regular cell metabolism, and originate under the influence of some external causes, such as ultraviolet light, cigarette smoke, environment pollution, gamma radiation or some pharmacological agents. ROS trigger macromolecular damage inside the cell (lipids, proteins, nucleic acids). Over the centuries of evolution, organisms have created defence mechanisms against reactive oxygen species. The role of those mechanisms, among other things, is to stop free radical chain reactions, block any reaction of oxygen free radicals with compounds vital for the organism, and cleanse the body of the effects of free radical reactions with body molecules. The defence system of the organisms consists of enzymes whose task is to decompose radical compounds, binding proteins which transport and store metal ions, and enzymes which have the role of repairing the damage caused by free radicals. Trace elements support the antioxidative system within the organism. Their activity consists in blocking chain reactions of free radicals, as well as controlling the reaction of free radicals with the components of the organism. As co-enzyme ingredients and structural elements of macromolecules, they also act as metabolism regulators.