Description
An antioxidant is a molecule that inhibits the oxidation of other
molecules. Oxidation is a chemical reaction that transfers
electrons or hydrogen from a substance to an oxidizing agent.
Oxidation reactions can produce free radicals. In turn, these
radicals can start chain reactions. When the chain reaction occurs
in a cell, it can cause damage or death to the cell. Antioxidants
terminate these chain reactions by removing free radical
intermediates, and inhibit other oxidation reactions. They do this
by being oxidized themselves, so antioxidants are often reducing
agents such as thiols, ascorbic acid, or polyphenols.
Antioxidants are important additives in gasoline. These
antioxidants prevent the formation of gums that interfere with the
operation of internal combustion engines.
Substituted phenols and derivatives of phenylenediamine are common
antioxidants used to inhibit gum formation in gasoline
(petrol).
Although oxidation reactions are crucial for life, they can also be
damaging; plants and animals maintain complex systems of multiple
types of antioxidants, such as glutathione, vitamin C, vitamin A,
and vitamin E as well as enzymes such as catalase, superoxide
dismutase and various peroxidases. Insufficient levels of
antioxidants, or inhibition of the antioxidant enzymes, cause
oxidative stress and may damage or kill cells.
As oxidative stress appears to be an important part of many human
diseases, the use of antioxidants in pharmacology is intensively
studied, particularly as treatments for stroke and
neurodegenerative diseases. Moreover, oxidative stress is both the
cause and the consequence of disease.
Antioxidants are widely used in dietary supplements and have been
investigated for the prevention of diseases such as cancer,
coronary heart disease and even altitude sickness. Although initial
studies suggested that antioxidant supplements might promote
health, later large clinical trials with a limited number of
antioxidants detected no benefit and even suggested that excess
supplementation with certain putative antioxidants may be harmful.
Antioxidants also have many industrial uses, such as preservatives
in food and cosmetics and to prevent the degradation of rubber and
gasoline.
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