Antioxidants

<p >An <b>antioxidant</b> is a <a href="http://en.wikipedia.org/wiki/Molecule" title="Molecule" >molecule</a> that inhibits the <a href="http://en.wikipedia.org/wiki/Redox" title="Redox" >oxidation</a> of other molecules. Oxidation is a <a href="http://en.wikipedia.org/wiki/Chemical_reaction" title="Chemical reaction" >chemical reaction</a> that transfers<a href="http://en.wikipedia.org/wiki/Electron" title="Electron" >electrons</a> or hydrogen from a substance to an <a href="http://en.wikipedia.org/wiki/Oxidizing_agent" title="Oxidizing agent" >oxidizing agent</a>. Oxidation reactions can produce <a href="http://en.wikipedia.org/wiki/Radical(chemistry)" title="Radical (chemistry)" >free radicals</a>. In turn, these radicals can start <a href="http://en.wikipedia.org/wiki/Chain_reaction" title="Chain reaction" >chain reactions</a>. When the chain reaction occurs in a <a href="http://en.wikipedia.org/wiki/Cell(biology)" title="Cell (biology)" >cell</a>, 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 <a href="http://en.wikipedia.org/wiki/Reducing_agent" title="Reducing agent" >reducing agents</a> such as <a href="http://en.wikipedia.org/wiki/Thiol" title="Thiol" >thiols</a>, <a href="http://en.wikipedia.org/wiki/Ascorbic_acid" title="Ascorbic acid" >ascorbic acid</a>, or <a href="http://en.wikipedia.org/wiki/Polyphenol_antioxidant" title="Polyphenol antioxidant" class="mw-redirect" >polyphenols</a>.<sup id="cite_ref-Sies_0-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Antioxidant#cite_note-Sies-0" >[1]</a></sup>

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Antioxidants are important additives in gasoline. These antioxidants prevent the formation of gums that interfere with the operation of internal combustion engines.<sup id="cite_ref-Ullmann_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Antioxidant#cite_note-Ullmann-1" >[2]</a></sup></p>

Substituted <a href="http://en.wikipedia.org/wiki/Phenol" title="Phenol" >phenols</a> and derivatives of<a href="http://en.wikipedia.org/wiki/P-Phenylenediamine" title="P-Phenylenediamine" >phenylenediamine</a> are common antioxidants used to inhibit gum formation in gasoline (petrol).</div>

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<p >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 <a href="http://en.wikipedia.org/wiki/Glutathione" title="Glutathione" >glutathione</a>, <a href="http://en.wikipedia.org/wiki/Vitamin_C" title="Vitamin C" >vitamin C</a>, and <a href="http://en.wikipedia.org/wiki/Vitamin_E" title="Vitamin E" >vitamin E</a> as well as <a href="http://en.wikipedia.org/wiki/Enzyme" title="Enzyme" >enzymes</a> such as <a href="http://en.wikipedia.org/wiki/Catalase" title="Catalase" >catalase</a>, <a href="http://en.wikipedia.org/wiki/Superoxide_dismutase" title="Superoxide dismutase" >superoxide dismutase</a> and various <a href="http://en.wikipedia.org/wiki/Peroxidase" title="Peroxidase" >peroxidases</a>. 

Low levels of antioxidants, or <a href="http://en.wikipedia.org/wiki/Enzyme_inhibitor" title="Enzyme inhibitor" >inhibition</a> of the antioxidant enzymes, cause <a href="http://en.wikipedia.org/wiki/Oxidative_stress" title="Oxidative stress" >oxidative stress</a> and may damage or kill cells.</p>

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As oxidative stress appears to be an important part of many human diseases, the use of antioxidants in <a href="http://en.wikipedia.org/wiki/Pharmacology" title="Pharmacology" >pharmacology</a> is intensively studied, particularly as treatments for stroke and <a href="http://en.wikipedia.org/wiki/Neurodegenerative_disease" title="Neurodegenerative disease" class="mw-redirect" >neurodegenerative diseases</a>. Moreover, oxidative stress is both the cause and the consequence of disease.</p>

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Antioxidants are widely used in <a href="http://en.wikipedia.org/wiki/Dietary_supplement" title="Dietary supplement" >dietary supplements</a> and have been investigated for the prevention of diseases such as cancer,<a href="http://en.wikipedia.org/wiki/Coronary_heart_disease" title="Coronary heart disease" class="mw-redirect" >coronary heart disease</a> and even <a href="http://en.wikipedia.org/wiki/Altitude_sickness" title="Altitude sickness" >altitude sickness</a>. Although initial studies suggested that antioxidant supplements might promote health, later large <a href="http://en.wikipedia.org/wiki/Clinical_trial" title="Clinical trial" >clinical trials</a> with a limited number of antioxidants detect no benefit and even suggested that excess supplementation with certain putative antioxidants may be harmful.<sup id="cite_ref-cardivascular_review_2-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Antioxidant#cite_note-cardivascular_review-2" >[3]</a></sup><sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Antioxidant#cite_note-3" >[4]</a></sup><sup id="cite_ref-4" class="reference" ><a href="http://en.wikipedia.org/wiki/Antioxidant#cite_note-4" >[5]</a></sup> Antioxidants also have many industrial uses, such as <a href="http://en.wikipedia.org/wiki/Preservative" title="Preservative" >preservatives</a> in food and cosmetics and to prevent the degradation of rubber and gasoline.</p>

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