Yeast comes in several forms -- including brewer's yeast in dried powder or tablets. The name comes from its use in brewing alcoholic beverages such as beer. Health stores offer brewer's yeast as a dietary supplement rich in B vitamins, even though only fortified brewer's yeast has vitamin B12.
Vitamin B12 plays an important role in metabolism, the nervous system and the creation of red blood cells, according to the University of Maryland Medical Center. A very complex vitamin, B12 occurs in many animal products, including dairy foods, fish and meat. Most people get enough B12 from their diet, although vegans may not. In addition 10 to 15 percent of those who are 60 and older are deficient in B12, according to Dr. Jane Higdon of the Linus Pauling Institute.
Yeast is a living single-celled organism. When used in brewing, it feeds on sugars and gives off carbon dioxide, helping in the fermentation process. It creates a bubbling froth at the top of the brewing liquid. Brewer's yeast offers a high concentration of B vitamins, including B1, B2, B3, B5, B6, B7 and B9. Vitamin B9 is also known as folic acid. B7 is biotin, and B2 is riboflavin. This is why you'll find brewer's yeast supplement pills in health food stores.
Several reputable sites, including the Department of Health and Human Services' GirlsHealth website, were listing brewer's yeast as a source of vitamin B12 as of May 2011. This is a mistake. Because brewer's yeast contains all other B vitamins, some stores and websites mistakenly assume that this includes B12. If you need a B12 supplement, brewer's yeast may not offer what you need.
Some brewer's yeast products come fortified with B12. That means that B12 is added into the yeast. But if you need a B12 supplement and want to get it from fortified brewer's yeast, study the packaging carefully. Vitamin B12 is sensitive to natural light. Fortified brewer's yeast exposed to light or left in an opened container may lose its B12 potency. Also, any brewer's yeast sold in unmarked packages cannot be verified as fortified with B12.