The Need for Vitamin B12
Vitamin B12 is needed for cell division and blood formation. Plant foods do not contain vitamin B12 except when they are contaminated by microorganisms. Thus, vegans need to look to other sources to get vitamin B12 in their diet. Although the minimum requirement for vitamin B12 is quite small, 1/1,000,000 of a gram (1 microgram) a day for adults [1], a vitamin B12 deficiency is a very serious problem leading ultimately to irreversible nerve damage. Prudent vegans will include sources of vitamin B12 in their diets. However, vitamin B12 deficiency is actually quite rare even among long-term vegans.Normally, vitamin B12 is secreted into the small intestine along with bile and other secretions and is reabsorbed, but this does not add to the body's vitamin B12 stores. Since small amounts of vitamin B12 are not reabsorbed, it is possible that eventually vitamin B12 stores will be used up. However, we may be quite efficient at re-using vitamin B12 so that deficiency is rare.
Bacteria in the human intestinal tract do make vitamin B12. The majority of these bacteria are found in the large intestine. Vitamin B12 does not appear to be absorbed from the large intestine [1].
Possible Vitamin B12 Sources
Some bacteria in the small intestine do produce vitamin B12 [2]. The amount of vitamin B12 which is produced does not appear adequate to prevent vitamin B12 deficiency [3].Although some vegans may get vitamin B12 from inadequate hand washing, this is not a reliable vitamin B12 source. Vegans who previously ate animal-based foods may have vitamin B12 stores that will not be depleted for 20 to 30 years [1] or more. However, long-term vegans, infants, children, and pregnant and lactating women (due to increased needs) should be especially careful to get enough vitamin B12.
Reliable Vegan Sources of Vitamin B12
A number of reliable vegan food sources for vitamin B12 are known. One brand of nutritional yeast, Red Star T-6635+, has been tested and shown to contain active vitamin B12. This brand of yeast is often labeled as Vegetarian Support Formula with or without T-6635+ in parentheses following this new name. It is a reliable source of vitamin B12. Nutritional yeast, Saccharomyces cerevisiae, is a food yeast, grown on a molasses solution, which comes as yellow flakes or powder. It has a cheesy taste. Nutritional yeast is different from brewer's yeast or torula yeast. It can often be used by those sensitive to other yeasts.The RDA (which includes a safety factor) for adults for vitamin B12 is 2.4 micrograms daily [4]. 2.4 micrograms of vitamin B12 are provided by a little less than 1 Tablespoon of Vegetarian Support Formula (Red Star T-6635+) nutritional yeast. A number of the recipes in this book contain nutritional yeast.
Another source of vitamin B12 is fortified cereal. We recommend checking the label of your favorite cereal since manufacturers have been known to stop including vitamin B12.
Other sources of vitamin B12 are vitamin B12-fortified soy milk, vitamin B12-fortified meat analogues (food made from wheat gluten or soybeans to resemble meat, poultry or fish), and vitamin B12 supplements. There are vitamin supplements which do not contain animal products.
Vegans who choose to use a vitamin B12 supplement, either as a single supplement or in a multi-vitamin should use supplements at least several times a week. Even though a supplement may contain many times the recommended level of vitamin B12, when vitamin B12 intake is high, not as much appears to be absorbed. This means in order to meet your needs, you should take the vitamin several times a week.
Tempeh, miso, and sea vegetables often are reported to have large amounts of vitamin B12. These products, however, are not reliable sources of the vita-min because the amount of vitamin B12 present depends on the type of processing the food undergoes [1, 5]. The standard method for measuring vitamin B12 in foods measures both active and inactive forms of vitamin B12. The inactive form (also called analogues) actually interferes with normal vita-min B12 absorption and metabolism [1, 6]. Fermented foods and sea vegetables may contain more inactive than active vitamin B12.
References
1. Herbert V. Vitamin B12: Plant sources, requirements, and assay. Am J Clin Nutr 1988; 48: 852-858.2. Albert MJ, Mathan VI, Baker SJ. Vitamin B12 synthesis by human small intestinal bacteria. Nature 1980; 283: 781-782.
3. Callender ST, Spray GH. Latent pernicious anemia. Br J Haematol 1962; 8: 230-240.
4. Institute of Medicine, Food and Nutrition Board: Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B-6, Folate, Vitamin B-12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press, 1998.
5. Specker BL, Miller D, Norman EJ, et al. Increased urinary methylmalonic acid excretion in breast-fed infants of vegetarian mothers and identification of an acceptable dietary source of vitamin B12. Am J Clin Nutr 1987; 47: 89-92.
6. Kondo H, Binder MJ, Kohhouse JF, et al. Presence and formation of cobal-amin analogues in multivitamin-mineral pills. J Clin Invest 1982; 70: 889-898.
7. Mozafar A. Is there vitamin B12 in plants or not? A plant nutritionist's view. Vegetarian Nutrition: An International Journal 1997; 1/2: 50-52.
8. Mozafar A. Enrichment of some B-vitamin in plants with application of organic fertilizers. Plant and Soil 1994; 167: 305-11.
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This article originally appeared in the book Simply Vegan: Quick Vegetarian Meals by Debra Wasserman. Nutrition section by Reed Mangels Ph.D., R.D. (ISBN 0-931411-20-3) |
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