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Recomended Daily Allowance
|Men: 2.0 mcg
Women: 2.0 mcg
|Men: 2.0 mcg
Women: 2.0 mcg
|Men: 1.5 mcg
Women: 1.5 mcg
Uses and Facts
Dietary supplement for normal growth, development
and health. Treatment for nerve damage. Treatment for pernicious anemia.
Treatment and prevention of vitamin B-12 deficiencies in people who have
had stomach or intestines surgically removed. Prevention of vitamin B-12
deficiency in strict vegetarians and persons with absorption diseases.
Vitamin B12, which is also known as cobalamin,
was the last B vitamin to be discovered. It is water soluble, bright red
in color and has a molecule of cobalt at its center. The average adult
body contains 2 to 5 mg of vitamin B12, with 80 per cent of this stored
in the liver.
OTHER SYMPTOMS Vitamin B12 is involved
in production of the genetic material of the cell and deficiency may cause
defective production which could lead to cancer. Low levels of Vitamin
B12 may also contribute to diabetic neuropathy, poor vision, osteoporosis,
recurrent yeast infections and infertility.
Vitamin B12 is essential for the release of
energy from food and plays a role in the metabolism of certain amino acids
and fats. Vitamin B12 is also essential for the conversion of inactive
folate to active folate. Rapidly dividing cells such as those in the epithelium
and bone marrow have the greatest need for vitamin B12.
A compound known as intrinsic factor which
is secreted by the cells lining the stomach is necessary for absorption
of vitamin B12 from the small intestine. Those with malabsorption problems
such as celiac disease, low stomach acid or who have had stomach or intestinal
surgery may have problems absorbing vitamin B12. Calcium and iron assist
with vitamin B12 absorption.
Vitamin B12 is excreted in the bile and
reabsorbed. Those on diets which are low in vitamin B12 may obtain more
from reabsorption than from food. Because of this reabsorption, vitamin
B12 deficiency can take many years to become apparent. The Schilling test,
which uses a small dose of radioactive vitamin B12 and then a larger dose
of normal B12 to flush this out, is used to measure the ability of a person
to absorb vitamin B12.
As the body stores vitamin B12, symptoms of
deficiency can take up to four to five years of poor dietary intake or
lack of intrinsic factor production to appear. Deficiency is more commonly
linked to the inability to absorb the vitamin due to lack of intrinsic
factor than to insufficient dietary intake. Subtle vitamin B12 deficiency
without obvious clinical signs may be relatively common in older people
with as many as 20 per cent of elderly men and women affected.
Vitamin B12 deficiency causes pernicious anemia
with symptoms of tiredness, pallor, lightheadedness, breathlessness, headache
and irritability. Red blood cells become abnormally enlarged and reduced
blood platelet formation causes poor clotting and bruising. A high intake
of folic acid can prevent the red blood cell changes caused by vitamin
B12 deficiency. It does not, however, prevent the nerve damage which may
only become apparent in later stages and which may not be reversible. Strict
vegetarians, whose folic acid intakes are high while their vitamin B12
intakes are low, may be at particular risk of nerve damage.
Vitamin B12 deficiency leads to reduced numbers
of white blood cells which causes increased susceptibility to infection.
Recent research has shown that elderly patients with low vitamin B12 levels
have impaired antibody response to bacterial vaccine, even in those with
no clinical signs of deficiency.
Brain and Nervous System
Vitamin B12 deficiency eventually leads to
a deterioration in mental functioning, to neurological damage and to a
number of psychological disturbances including memory loss, disorientation,
numbness, dementia, moodiness, confusion and delusions. Alzheimer’s disease
sufferers are often found to have low vitamin B12 levels although it is
unclear whether these are a contributing factor or a result of the disease.
B12 deficiency leads to a loss of nerve-insulating myelin which begins
at the peripheral nerves and eventually moves up to the spine causing decreased
reflexes, abnormal gait, weakness, fatigue, poor vision and impaired touch
or pain sensation. Other signs include tingling or loss of sensation and
weakness in hands and feet and diminished sensitivity to vibration and
Vitamin B12 deficiency causes poor cell formation
in the digestive tract and leads to nausea, vomiting, loss of appetite,
poor absorption of food, soreness of the mouth and tongue, and diarrhea.
Good sources of vitamin B12 include liver
and organ meats, muscle meats, chicken, fish, eggs, shellfish, milk and
most dairy products. Sea vegetables and fermented soybean products such
as miso also contain forms of vitamin B12, although some research suggests
that the human body may not be able to absorb these forms and they may
even block true vitamin B12 absorption.
Many vegetarian and vegan products are
fortified with vitamin B12, including yeast extract, vegetable stock and
soya milk. Due to the importance of B12 vegetarian need to be sure they
are receiving adequate amounts.
Cooking has little effect on vitamin B12
although some may be lost when food is cooked to temperatures above 100
Vitamin B12 is available in several forms.
Cyanocobalamin is the main synthetic form and has a cyanide molecule attached.
Methylcobalamin is one of two active forms of vitamin B12 and may be a
more effective supplement.
Vegans are at particular risk of vitamin
B12 deficiency and may benefit from supplements.
Vitamin B12 tablets should be taken one
hour before food. Low dose supplementary vitamin A may be beneficial in
the elderly and in those who cannot absorb fats. Vitamin A needs may be
increased in cases of trauma, anxiety, stress, alcohol use and smoking.
Vitamin B12 works closely with folic acid
and vitamin B6 in a number of body functions. A vitamin E deficiency may
reduce the conversion of vitamin B12 to its active form. Vitamin B6 deficiency
reduces vitamin B12 absorption.
Acids and alkalis, water, sunlight, alcohol,
estrogen and sleeping pills can destroy vitamin B12.
Antacids, anti-epileptic drugs, cholestyramine
and colchicine (for gout) may decrease vitamin B12 absorption.
Large doses of vitamin C can increase excretion
of vitamin B12.
Chloramphenicol and other bone marrow suppressant
drugs may interfere with the red blood cell functions of vitamin B12.
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