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. </p>
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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>. </p>
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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>. </p>
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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. </p>
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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></p>
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Antioxidants are important additives in gasoline. These antioxidants prevent the formation of <a href="http://en.wikipedia.org/wiki/Gums" title="Gums" class="mw-redirect" >gums</a> 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>
<sup id="cite_ref-Ullmann_1-0" class="reference" > </sup>
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>. </p>
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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>. </p>
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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>. </p>
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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 detected 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> </p>
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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>