Editing Dietary supplement (section)

===Vitamins===
{{main|Vitamin}}
[[File:VitaminSupplementPills.jpg|thumb|right|Pharmacies and supermarkets in the U.S. sell a large variety of vitamin dietary supplements.]]

A vitamin is an [[organic compound]] required by an [[organism]] as a vital [[nutrient]] in limited amounts.<ref name="Lieberman">Lieberman, S and Bruning, N (1990). ''The Real Vitamin & Mineral Book''. NY: Avery Group, 3, {{ISBN|0-89529-769-8}}.</ref> An organic chemical compound (or related set of compounds) is called a vitamin when it cannot be [[biosynthesis|synthesized]] in sufficient quantities by an organism and must be obtained from the diet. The term is conditional both on the circumstances and on the particular organism. For example, [[ascorbic acid]] (vitamin C) is a vitamin for anthropoid primates, [[human]]s, [[guinea pig]]s and [[bat]]s, but not for other mammals. Vitamin D is not an essential nutrient for people who get sufficient exposure to [[Ultraviolet light therapy|ultraviolet light]], either from the sun or an artificial source, as they synthesize vitamin D in skin.<ref>{{cite journal | vauthors = Drouin G, Godin JR, Pagé B | title = The genetics of vitamin C loss in vertebrates | journal = Current Genomics | volume = 12 | issue = 5 | pages = 371–78 | date = August 2011 | pmid = 22294879 | pmc = 3145266 | doi = 10.2174/138920211796429736 }}</ref> Humans require thirteen vitamins in their diet, most of which are actually groups of related molecules, "vitamers", (e.g. vitamin E includes [[tocopherol]]s and [[tocotrienol]]s, vitamin K includes vitamin K<sub>1</sub> and K<sub>2</sub>). The list: vitamins A, C, D, E, K, Thiamine (B<sub>1</sub>), Riboflavin (B<sub>2</sub>), Niacin (B<sub>3</sub>), Pantothenic Acid (B<sub>5</sub>), Vitamin B<sub>6</sub>, Biotin (B<sub>7</sub>), Folate (B<sub>9</sub>) and Vitamin B<sub>12</sub>. Vitamin intake below recommended amounts can result in signs and symptoms associated with vitamin deficiency. There is little evidence of benefit when vitamins are consumed as a dietary supplement by those who are healthy and have a nutritionally adequate diet.<ref name=Fort2013>{{cite journal | vauthors = Fortmann SP, Burda BU, Senger CA, Lin JS, Whitlock EP | title = Vitamin and mineral supplements in the primary prevention of cardiovascular disease and cancer: An updated systematic evidence review for the U.S. Preventive Services Task Force | journal = Annals of Internal Medicine | volume = 159 | issue = 12 | pages = 824–34 | date = December 2013 | pmid = 24217421 | doi = 10.7326/0003-4819-159-12-201312170-00729 | doi-access = free }}</ref>

The [[National Academy of Medicine|U.S. Institute of Medicine]] sets [[tolerable upper intake level]]s (ULs) for some of the vitamins. This does not prevent dietary supplement companies from selling products with content per serving higher than the ULs. For example, the UL for vitamin D is 100&nbsp;μg (4,000 IU),<ref name=IOM>{{citation| title = Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals| publisher = Food and Nutrition Board, Institute of Medicine, National Academies| year = 2004| url = https://www.nal.usda.gov/fnic/dri-tables-and-application-reports| archive-url = https://web.archive.org/web/20170118124310/https://www.nal.usda.gov/fnic/dri-tables-and-application-reports| url-status = dead| archive-date = January 18, 2017| access-date = 2009-06-09}}</ref> but products are available without prescription at 10,000 IU.