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<p><em>Vitamin B-12</em> is the name for a class of chemically-related compounds, all of which have vitamin activity. It is structurally the most complicated vitamin. Biosynthesis of the basic structure of the vitamin can only be accomplished by bacteria, but conversion between different forms of the vitamin can be accomplished in the human body. A common form of the vitamin, cyanocobalamin, does not occur in nature, but is used as a supplement and food additive, due to its stability. It is converted to other forms of the vitamin which are actually used in chemical reactions in the body.</p>

<p>Historically, vitamin B-12 was discovered from its relationship to the disease pernicious anemia, which was eventually discovered to result from an effective lack of this vitamin due to problems with the mechanisms in the body which normally absorb it. Many other subtler kinds of vitamin B12 deficiency, and their biochemical effects, have since been elucidated.</p>

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<h2><span class="mw-headline">Terminology</span></h2>

<li><a class="external text" title="http://www.healthaliciousness.com/articles/foods-high-in-vitamin-B12.php" rel="nofollow" href="http://www.healthaliciousness.com/articles/foods-high-in-vitamin-B12.php">Top Ten Foods Highest in Vitamin B12</a> </li>

<li><a title="Medical Subject Headings" href="http://en.wikipedia.org/wiki/Medical_Subject_Headings">MeSH</a> <em><a class="external text" title="http://www.nlm.nih.gov/cgi/mesh/2008/MB_cgi?mode=&amp;term=Cyanocobalamin" rel="nofollow" href="http://www.nlm.nih.gov/cgi/mesh/2008/MB_cgi?mode=&amp;term=Cyanocobalamin">Cyanocobalamin</a></em> </li>

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