The Viva Vine: vol #6, no #1: January / February, 1997

The Vegan Achilles Heel

A little can mean a lot--the truth about vitamin B-12

by Marcella M. Modugno

Guest writer Marcella Modugno recently worked as an intern with the VivaVegie Society.

Since vitamin B-12 originates or resides in animal foods and earthy environments, not getting enough of it can be a problem for vegans who not only avoid meat but may also have little contact with the soil. Though not common--because so little of the nutrient is necessary for human health--deficiencies can be serious.

What exactly is vitamin B-12? Known as cobalamin, this vitamin functions mainly as a coenzyme in fat and carbohydrate metabolism. A chemical component of gastric juice called "intrinsic factor" is required for the absorption of this vitamin. Without it, B-12 cannot go through its normal biochemical pathways and pernicious anemia will develop. Vitamin B-12 is also involved in the production of myelin, the sheath that covers our nerves. Thus, the association between B-12 deficiency and impaired nervous-system function is well established.

An impaired nervous system is an extremely serious condition. In adults, the neurological symptoms develop slowly and are not always obvious. By the time some patients get treated, the nerve damage they have suffered cannot be completely reversed. Numbness or tingling in the limbs, memory loss and feelings of weakness or trouble with balance when walking are the most common signs of nerve impairment from B-12 deficiency. An anemia of developing red blood cells, known as megaloblastic anemia, can occur in adults and children. Infants get more obvious symptoms that can stunt growth and development. An infant can progress from normal to critically ill in a matter of weeks, showing signs such as an inability to respond to stimuli, decreased brain growth and loss of head control. Obviously, getting enough B-12 for the body is an important concern for everyone, but it is a serious concern for vegans.

Why is this so? The reason is that B-12 is produced by bacteria. In earlier times, society had a connection with soil and unpurified water, where B-12 is abundant. In fact, it stands to reason that the natural foods to eat to obtain B-12 are potatoes, carrots and mushrooms-all of which grow in or close to the soil. However, mushrooms (wild morel and oyster) are the only foods that are thought to come out of the ground with their own B-12. They contain about a third of a day's requirement in a 100-gram serving.

Today, most of society gets water from the tap and purchases its food and does not connect with the B-12 bacteria. It might be interesting to note that the bacteria in our large intestines manufacture all the B-12 we need. The problem is that the B-12 we produce cannot get back up to the small intestine, where it needs to be absorbed. This means that our ability to manufacture B-12 is pretty useless from a nutritional standpoint. Fortunately, the body needs only a very small amount of B-12 for the nutrient to do its enormous job of assisting in the proper formation of red blood cells and nerves. To allow for biological variation and the maintenance of body stores, the RDA (Recommended Daily Allowance) for B-12 is 2 micrograms. This is actually a lot more than most people need. You could get all the B-12 you need in a day from regularly eating one carrot containing just a trace of bacteria-produced B-12 (an organic carrot, for instance). Vegans often don't eat even one "contaminated" carrot a day, however, so they must get their B-12 from other sources.

B-12 is found primarily in animal foods (because of the bacteria that live in their digestive tracts). Meat-eaters can obtain B-12 in meat, dairy products and eggs. Yogurt, by the way, is an unreliable source of B-12 because the culture bacteria ingest most of it. Therefore, it would take an enormous amount of yogurt to fulfill the adult RDA. Vegans can obtain B-12 by eating fortified plant foods or those plant foods "contaminated" by the proper bacteria.

There has been a trend towards fortifying commercial breakfast cereals with B-12. This would be encouraging were it not for the products involved. Case in point: Most cereals are made from grains that have been exploded ("popped," "puffed" or "crisped," etc.) in such a way as to fill them with air. The temperatures required scorch the vitamin content of the grains into oblivion, and manufacturers put only a small fraction back in. The idea of removing all the vitamins from their natural sources and then replacing them one by one is a little strange, but in the case of B-12 this makes sense because it is rarely found in grains to begin with. Other fortified foods would be breads, pastas, crackers and prepared foods. And if you choose, do your own fortifying. Red Star brand fortified nutritional yeast labeled T-6635+ is a stable source of B-12, and it can be added to other foods.

Another way for vegans to go is to take B-12 supplements. It is best to take a single B-12 tablet that lists its source as cyano-cobalamin instead of a multivitamin containing B-12. The other vitamins and minerals in a multivitamin might interfere with B-12's potency and effectiveness. The table below lists the RDAs that should be followed for most age groups:

Infants: 0.3 micrograms/day
Preadolescent children: 0.05 micrograms/kg of body weight
Adults: 2 micrograms/day
During pregnancy: 4 micrograms/day
Elderly: 2 micrograms/day

A dietary intake of 1 microgram daily can be expected to sustain average adults. The RDAs are set at the levels indicated above to allow for substantial stores of B-12.

Most vegans do have substantial stores of B-12 available. However, there will always be some people who are deficient. Since it is hard to determine who is deficient, the safest thing to do is to take a supplement. This will keep all vegans within the safe and adequate ranges of the RDA.

It is not necessary for anyone to eat meat or dairy products in order to get enough of this vitamin. The very small amount of B-12 required for it to perform its duties is well within the reach of everyone. There are many benefits associated with a vegan diet. Who would want to spoil all that just for 2 micrograms of B-12? For further information about your nutritional intake, consult a registered dietitian in your own area.

References

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  2. Havala S., Dwyer J. "Position of the American Dietetic Association: Vegetarian Diets-Technical Support Paper." J. Am. Diet. Assoc. 1988; 88:352-355.
  3. Herbert V.; Subak-Sharpe, G.J. Total Nutrition: The Only Guide You'll Ever Need-From the Mount Sinai School of Medicine. New York, NY: St. Martin's Press; 1995.
  4. Lieberman, S.; Bruning N. The Real Vitamin & Mineral Book. Garden City Park, NY: Avery Publishing Group, Inc.; 1990.
  5. Mahan K.L.; Arlin M. Krause's Food, Nutrition & Diet Therapy, 8th ed. Philadelphia, PA: W.B. Saunders Company; 1992.
  6. Food and Nutrition Board. Recommended Daily Allowances, 10th ed. Washington, DC: National Academy Press; 1989.
  7. Wentzler, R. The Vitamin Book. New York, NY: Gramercy Publishing Company; 1978.
  8. Williams, S.R. Basic Nutrition and Diet Therapy, 9th ed. St. Louis, MO: Mosby Year Book; 1992.

Marcella M. Modugno holds a B.S. in dietetics from the University of New Haven in Connecticut. She is currently studying in a coordinated program at New York University, which will enable her to get her M.S. in food and nutrition and complete her dietetic internship at the Bronx VA Medical Center.



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