Editing Tocopherol (section)

==Function and dietary recommendations==
{{Main|Vitamin E}}
[[File:TocophMech.svg|thumb|left|360px|class=skin-invert-image|Tocopherols function by donating H atoms to radicals (X).]]

===Mechanism of action===
Tocopherols are radical scavengers, delivering an H atom to quench free radicals. At 323&nbsp;kJ/mol, the O–H bond in tocopherols is approximately 10% weaker than in most other [[phenol]]s.<ref>{{RubberBible87th}}</ref> This weak bond allows the vitamin to donate a hydrogen atom to the [[peroxyl radical]] and other [[Radical (chemistry)|free radicals]], minimizing their damaging effect. The thus generated tocopheryl radical is relatively unreactive, but reverts to tocopherol by a [[redox]] reaction with a hydrogen donor such as [[vitamin C]].<ref>{{cite journal | vauthors = Traber MG, Stevens JF | title = Vitamins C and E: beneficial effects from a mechanistic perspective | journal = Free Radical Biology & Medicine | volume = 51 | issue = 5 | pages = 1000–1013 | date = September 2011 | pmid = 21664268 | pmc = 3156342 | doi = 10.1016/j.freeradbiomed.2011.05.017 }}</ref> As they are fat-soluble, tocopherols are incorporated into cell membranes, which are thus protected from oxidative damage.

===Dietary considerations===
The U.S. Recommended Dietary Allowance (RDA) for adults is 15&nbsp;mg/day.<ref name="DRItext"/> The RDA is based on the α-tocopherol form because it is the most active form as originally tested. Vitamin E supplements are absorbed best when taken with meals.<ref>{{cite journal | vauthors = Iuliano L, Micheletta F, Maranghi M, Frati G, Diczfalusy U, Violi F | title = Bioavailability of vitamin E as function of food intake in healthy subjects: effects on plasma peroxide-scavenging activity and cholesterol-oxidation products | journal = Arteriosclerosis, Thrombosis, and Vascular Biology | volume = 21 | issue = 10 | pages = E34–E37 | date = October 2001 | pmid = 11597949 | doi = 10.1161/hq1001.098465 | doi-access = free }}</ref> The U.S. Institute of Medicine has set an upper tolerable intake level (UL) for vitamin E at 1,000&nbsp;mg (1,500&nbsp;IU) per day.<ref name="GOVe">{{cite web |author1=National Institutes of Health |author1-link=NIH |title=Vitamin E: Facts Sheet for Health Professionals |url=https://ods.od.nih.gov/factsheets/VitaminE-HealthProfessional/ |website=Dietary Supplement Fact Sheets |publisher=Office of Dietary Supplements |access-date=19 May 2021 |language=en |date=26 March 2021}}</ref> The [[European Food Safety Authority]] sets UL at 300&nbsp;mg α-tocopherol equivalents per day.<ref name=EFSA-UL>{{citation |title = Tolerable Upper Intake Levels For Vitamins And Minerals |publisher = European Food Safety Authority |year = 2006 |url = http://www.efsa.europa.eu/sites/default/files/efsa_rep/blobserver_assets/ndatolerableuil.pdf |url-status = live |archive-url = https://web.archive.org/web/20160316225123/http://www.efsa.europa.eu/sites/default/files/efsa_rep/blobserver_assets/ndatolerableuil.pdf |archive-date = 2016-03-16}}.</ref>

===α-Tocopherol equivalents===
For dietary purposes, vitamin E activity of vitamin E [[isomers]] is expressed as α-tocopherol equivalents (a-TEs). One a-TE is defined by the biological activity of 1&nbsp;mg (natural) d-α-tocopherol in the resorption-gestation test. According to listings by [[FAO]] and others β-tocopherol should be multiplied by 0.5, γ-tocopherol by 0.1, and α-tocotrienol by 0.3.<ref name=fao1 /> The IU is converted to aTE by multiplying it with 0.67.<ref>{{cite web |url=http://www.ncc.umn.edu/products/databaseNUTvitamins.html |title=Vitamins |access-date=2013-03-26 |url-status=dead |archive-url=https://web.archive.org/web/20130320015716/http://www.ncc.umn.edu/products/databaseNUTvitamins.html |archive-date=2013-03-20 |publisher=University of Minnesota Nutrition Coordinating Center on Vitamins}}</ref> These factors do not correlate with the antioxidant activity of vitamin&nbsp;E isomers, where [[tocotrienols]] show even much higher activity in vivo.<ref name="pmid11160563">{{cite journal | vauthors = Packer L, Weber SU, Rimbach G | title = Molecular aspects of alpha-tocotrienol antioxidant action and cell signalling | journal = The Journal of Nutrition | volume = 131 | issue = 2 | pages = 369S–373S | date = February 2001 | pmid = 11160563 | doi = 10.1093/jn/131.2.369S | doi-access = free }}</ref>