Oxygen free radicals and human diseases

Free radicals and other reactive oxygen species are constantly formed in the human body. Many of them serve useful physiological functions, but they can be toxic when generated in excess and this toxicity is often aggravated by the presence of ions of such transition metals as iron or copper. Excess generation of reactive oxygen species within tissues can damage DNA, lipids, proteins and carbohydrates. Which of these is the most important target of damage depends upon the cell type subjected to the oxidative stress and upon how it is imposed.