COLLOIDAL MINERALS
VITAMIN B-12
VITAMIN B-12
Vitamin B-12 (cobalamin), stored in the liver, is a co-factor for two coenzymes.
Methyl-cobalamin catalyzes methyl group transfer from a folic acid co-factor
to form methionine. The unmethylated folate co-factor then participates in single
carbon reactions for nucleic acid synthesis. Thus some symptoms of vitamin B-12
and folic deficiencies are similar. The B-12 coenzyme deoxyadenosylcobalamin
catalyzes amino and fatty acid breakdown. Vitamin B-12
(cobalamin)
VITAMIN B-12 Deficiencies: Stages of deficiencies include: I (early)
- lower serum holotranscobalamin (holoTC II) (<60 pg/ml); II - lower serum vitamin
B-12 (<300 pg/ml) and holoTC II (<40 pg/ml); III -serum vitamin B-12 < 200 pg/ml
and holoTC II <40 pg/ml, neutrophil hypersegmentation, elevated homocysteine
and methylmalonic acid; and IV (severest) - also megaloblastic, macrocytic anemia.
Around Stage III (before anemia) there may be potentially irreversible demyelination
of spinal cord, brain and optic and peripheral nerves which produces peripheral
neuropathy progressing to subacute combined degeneration. Early symptoms may
be dementia, poor attention span and depression. Vitamin
B-12 (cobalamin)
The stomach secretes intrinsic factor that binds vitamin B-12 and mediates
its absorption at receptor sites in the ileum. Inadequate intrinsic factor secretion
occurs in pernicious anemia, an autoimmune disease. In the elderly, atrophic
gastritis is commonly associated with vitamin B-12 malabsorption and deficiency.
Because the absorbed vitamin is secreted in bile and subsequently reabsorbed,
deficiency symptoms can take 20 years to develop from low intakes, e.g., in
strict vegetarians. However, in malabsorption, deficiency occurs in months or
a few years because absorption from both the diet and enterohepatic circulation
is impaired.
VITAMIN B-12 Diet recommendations: The Recommended Dietary Allowances
(RDAs) are: 0 - 0.5 years, 0.3 µg; 0.5 - 1 year, 0.5 µg; 1 - 3 years, 1.0 µg;
4 - 6 years, 1.0 µg; 7 - 10 years, 1.4 µg; adolescents and adults, 2.0 µg; pregnancy,
2.2 µg; and lactation, 2.6 µg/day. Usual intakes are about 4 - 8 µg/day. Pregnant/lactating
women and long-term strict vegetarians should take supplements providing the
RDA. Vitamin B-12
VITAMIN B-12 Food sources: Vitamin B-12 is found only in animal products.
Excellent sources (>10 µg/100 g) include organ meats and bivalve mollusks such
as clams and oysters. Moderate amounts (1-10 µg/100 g) are contained in egg
yolks, muscle meats and poultry, fish, fermented cheeses and dry milk. Milk
and milk products contain <1 µg/100 g. Algae such as nori and spirulina contain
only vitamin B12 analogs that are biologically inactive
in humans. Vitamin B-12
VITAMIN B-12 Toxicity: No toxic effects have been reported when up
to 100 µg/day are consumed. Intramuscular injections of 100 µg are usually given
once/month to individuals who cannot absorb the vitamin through their intestine
because of pernicious anemia or other problems. Vitamin
B
VITAMIN B-12 Recent research: Vitamin B-12 deficiency may increase
the risk of neural tube defects in pregnant women with a high risk of this condition.
Vitamin B-12 deficiency may be common in AIDS and also in developing countries,
probably due to malabsorption combined with low intakes.
For further information:
Herbert, V. (1996) Vitamin B-12. In: Present Knowledge in Nutrition (Filer,
L.J. & Ziegler, E., eds.), 7th ed., pp. 191-205. International Life Sciences
Institute Press, Washington, DC V
Allen, L.H. & Casterline, J. (1994) Vitamin B-12 deficiency in the elderly:
diagnosis and requirements. Am. J. Clin. Nutr. 60: 12-14. Vitamin B-12
Chondroitin Sulfate
& Glucosamine Sulfate
Manganese (Mn) is an essential
trace mineral
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