An antioxidant is a chemical that reduces the rate of particular oxidation reactions in a specific context, where oxidation reactions are chemical reactions that involve the transfer of electrons from a substance to an oxidising agent.
Antioxidants are particularly important in the context of organic chemistry and biology: all living cells contain complex systems of antioxidant chemicals and/or enzymes to prevent chemical damage to the cells' components by oxidation. The importance and complexity of antioxidants in biology is reflected in a medical literature of more than 142,000 scholarly articles.
A diet containing antioxidants from plants are required for good health since plants are an important source of organic antioxidant chemicals. Antioxidants are widely used as ingredients in dietary supplements that are used for health purposes such as preventing cancer and heart disease.
However, while many studies have suggested benefits for antioxidant supplements, several large clinical trials have failed to clearly demonstrate a benefit for the formulations tested, and excess supplementation may be harmful.
Antioxidants are chemicals that reduce oxidative damage to cells and biochemicals. Researchers have found high correlation between oxidative damage and the occurrence of disease. For example, LDL oxidation is associated with cardiovascular disease.
The process leading to atherogenesis, atherosclerosis, and cardiovascular disease is complex, involving multiple chemical pathways and networks, but the precursor is LDL oxidation by free radicals, resulting in inflammation and formation of plaques.
Research suggests that consumption of antioxidant-rich foods reduces damage to cells and biochemicals from free radicals. This may slow down, prevent, or even reverse certain diseases that result from cellular damage, and perhaps even slow down the natural aging process.
Since the discovery of vitamins, it has been recognized that antioxidants in the diet are essential for healthful lives. More recently, a large body of evidence has accumulated that suggests supplementation of the diet with various kinds of antioxidants can improve health and extend life.
Many nutraceutical and health food companies now sell forms of antioxidants as dietary supplements. These supplements may include specific antioxidant chemicals, like resveratrol (from grape seeds), combinations of antioxidants, like the "ACES" products that contain beta carotene (provitamin A), vitamin C, vitamin E and Selenium, or specialty herbs that are known to contain antioxidants such as green tea and jiaogulan.