(also cyanocobamin)
| ...From the pages of Agricultural Research magazine |
Are You Vitamin B12 Deficient?
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Nearly
two-fifths of the U.S. population may be flirting
with marginal vitamin B12 status—that is,
if a careful look at nearly 3,000 men and women in
the ongoing Framingham (Massachusetts) Offspring
Study is any indication. Researchers found that 39
percent of the volunteers have plasma B12
levels in the "low normal" range—below 258 picomoles
per liter (pmol/L).
While this is well above the currently accepted deficiency level of 148 pmol/L, some people exhibit neurological symptoms at the upper level of the deficiency range, explains study leader Katherine L. Tucker. She is a nutritional epidemiologist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston. "I think there's a lot of undetected vitamin B12 deficiency out there," says Tucker. She noted that nearly 9 percent of the study population fell below the current deficiency level. And more than 16 percent fell below 185 pmol/L. "Many people may be deficient at this level," she says. "There is some question as to what the clinical cutoff for deficiency should be." Deficiency can cause a type of anemia marked by fewer but larger red blood cells. It can also cause walking and balance disturbances, a loss of vibration sensation, confusion, and, in advanced cases, dementia. The body requires B12 to make the protective coating surrounding the nerves. So inadequate B12 can expose nerves to damage. Tucker and colleagues wanted to get a sense of B12 levels spanning the adult population because most previous studies have focused on the elderly. That age group was thought to be at higher risk for deficiency. The researchers also expected to find some connection between dietary intake and plasma levels, even though other studies found no association. Some of the results were surprising. The youngest group—the 26 to 49 year olds—had about the same B12 status as the oldest group—65 and up. "We thought that low concentrations of B12 would increase with age," says Tucker. "But we saw a high prevalence of low B12 even among the youngest group."
The good news is that for many people, eating more fortified cereals and dairy products can improve B12 status almost as much as taking supplements containing the vitamin. Supplement use dropped the percentage of volunteers in the danger zone (plasma B12 below 185 pmol/L) from 20 percent to 8. Eating fortified cereals five or more times a week or being among the highest third for dairy intake reduced, by nearly half, the percentage of volunteers in that zone—from 23 and 24 percent, respectively, to 12 and 13 percent.
The researchers found no association between plasma B12 and meat, poultry, and fish intake, even though these foods supply the bulk of B12 in the diet. "It's not because people aren't eating enough meat," Tucker says. "The vitamin isn't getting absorbed."
The vitamin is tightly bound to proteins in meat and dairy products and requires high acidity to cut it loose. As we age, we lose the acid-secreting cells in the stomach. But what causes poor absorption in younger adults? Tucker speculates that the high use of antacids may contribute. But why absorption from dairy products appears to be better than from meats is a question that needs more research. Fortified cereals are a different story. She says the vitamin is sprayed on during processing and is "more like what we get in supplements."—By Judy McBride, Agricultural Research Service Information Staff. This research is part of Human Nutrition, an ARS National Program (#107) described on the World Wide Web at http://www.nps.ars.usda.gov/programs/appvs.htm. Katherine L. Tucker is at the Jean Mayer USDA-ARS Human Nutrition Research Center on Aging at Tufts University, 711 Washington St., Boston, MA 02111; phone (617) 556-3351, fax (617) 556-3344. |
| "Are You Vitamin B12 Deficient?" was published in the August 2000 issue of Agricultural Research magazine. | |
The requirement for vitamin B12 is very low. Non-animal sources include Red Star Vegetarian Support Formula or T-6635+ nutritional yeast (a little less than 1 Tablespoon supplies the adult RDA), and vitamin B12 fortified soymilk. It is especially important for pregnant and lactating women, infants, and children to have reliable sources of vitamin B12 in their diets.
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].
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.
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 Vegetar-ian 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 recom-mended 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 vege-tables may contain more inactive than active vitamin B12.
Some vitamin B12 appears to be found in organically grown plants, but in extremely small amounts. According to one study [7,8], more than 23 cups of organically grown spinach would have to be eaten every day in order to meet the adult RDA for vitamin B12. Produce cannot be depended on as a reliable vitamin B12 source because the level of vitamin B12 in plants varies widely depending on the type of plant and the soil in which it is grown. Also, vitamin B12 analogues may be found in soil and absorbed by plants. If these ana-logues are present, they could either interfere with the plants uptake of vitamin B12 or with the usefulness of the plant's vitamin B12 for humans.
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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