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.
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
analogues 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.
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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