Antioxidant

An antioxidant is any substance capable of preventing the loss of electrons (oxidation) from a molecule in the body. This rather broad definition can encompass many different chemical compounds, and these compounds can prevent the loss of electrons in many different ways. The opposite of an antioxidant is an oxidant, which strips electrons from molecules in the body. A compound that is an antioxidant in one chemical environment may become an oxidant in another chemical environment.

The oxidation (stripping of electrons) of a molecule in the body can be a deleterious action. Excessive oxidation is called "oxidative stress" and can lead to cell death. Oxidative stress often results from inflammatory processes, excessive metabolic activity, or from mitochondrial dysfunction. The main oxidants in these processes are reactive oxygen species (ROS), which include some free radicals. Antioxidants, therefore, can theoretically prevent harmful oxidative stress by neutralizing oxidants or by protecting molecules from oxidants.