Vitamin B12
Vitamin B12 is synthesized by bacteria in the gut and exists in all foods from
animal sources. The stomach secretes a substance called intrinsic factor that is
necessary for vitamin B12 to be absorbed. Calcium is also needed for proper
absorption to occur. Vitamin B12 is used with folic acid to prevent heart
disease. It is used for nerve pain, ringing in the ear, and numbness and
tingling in the feet and hands. It helps decrease symptoms of confusion, mood
changes, depression and multiple sclerosis in some people. Vitamin B12 is
necessary for the body to make red blood cells and keep the immune system
functioning. Vitamin B12 has been used in those with asthma, fatigue, hepatitis,
insomnia, epilepsy and infertility. Vitamin B12 is stored in the liver but
excess amounts are easily excreted in the urine. It is very safe and no side
effects or toxicity have been reported. Nitrous oxide, seizure drugs and alcohol
will decrease the levels of vitamin B12 in the blood. People with
gastrointestinal diseases that cause absorption problems, including Crohn's
disease, ulcers and sprue, may have a vitamin B12 deficiency. Vitamin C
increases the absorption of cyanocobalamin. Symptoms of a vitamin B12 deficiency
include numbness, pins-and-needles sensations, or a burning feeling in the feet
and hands. Fatigue, muscle weakness, confusion, loss of memory and depression
are other symptoms. Heart disease, including high serum cholesterol may be
present. Anemia will also occur. Deficiencies are most common in the elderly and
alcoholics. The Recommended Daily Allowance for vitamin B12 is 2.0 micrograms
per day. Supplements in the range of 1,000 to 5,000 micrograms per day have been
given. Animal sources, including liver and kidney, eggs, fish, cheese, and meat
are the best sources of vitamin B12. Milk and dairy products are also sources
but contain lesser amounts.
Other names
Cyanocobalamin, hydroxycobalamin, adenosylcobalamin, methylcobalamin
Uses
Vitamin B12 is given with folic acid and B6 to prevent heart disease due to high
levels of homocysteine. It is used for problems in the nervous system including,
nerve pain, ringing in the ear, and numbness and tingling. It is also used in
depression, psychosis, irritability, confusion, and mood changes. Vitamin B12
has been supplemented in those with Alzheimer's disease and multiple sclerosis.
It is important for proper functioning of the immune system and can slow the
progression of HIV to AIDs. It may be needed to prevent anemia. It may also help
with asthma, fatigue, hepatitis, insomnia, epilepsy and infertility.
Proposed Mechanism of Action
Vitamin B12 acts as a methyl donor in many reactions. This methyl group is added
to homocysteine, converting it to methionine. High homocysteine levels have been
associated with an increased risk of heart disease and high cholesterol. High
homocysteine is also associated with osteoporosis, and Alzheimer's disease.
Methionine is needed for the synthesis of choline. A lack of choline may lead to
impaired fatty acid synthesis and a decreased production of myelin, the sheath
that covers the nerves, resulting in a nervous system dysfunction. Cobalamin is
a cofactor in the production of some neurotransmitters, including serotonin and
dopamine. Low levels of serotonin have been associated with depression.
Vitamin B12 is needed for the secretion of melatonin, a hormone needed for a
proper sleep cycle. Low levels of vitamin B-12 may result in poor sleep.
Vitamin B12 forms a complex with sulfite and can prevent allergic reactions and
asthma in sulfite sensitive people. It is involved in the production of DNA and
RNA for cell replication. It is necessary for red blood cell production and for
proper immune function.
Side Effects / Precautions
Vitamin B12 is readily excreted in the urine. There have been no side effects or
toxicity reported. Supplements of vitamin B12 will cover up a folic acid
deficiency so it is important to distinguish between the two before treatment.
Interactions
There are few interactions with vitamin B12. Nitrous oxide, a general anesthetic
used primarily during dental procedures, lowers the blood levels. Antiepileptic
or seizure drugs and alcohol will also decrease the levels in the blood. People
with gastrointestinal diseases that cause absorption problems, including Crohn's
disease, ulcers and sprue, may have a vitamin B12 deficiency.
Vitamin C increases the absorption of cyanocobalamin.
Vitamin B12 is needed for the secretion of melatonin, a hormone needed for a
proper sleep cycle. Low levels of vitamin B-12 may result in poor sleep. Vitamin
B12 supplements may mask a folic acid deficiency.
Symptoms of Deficiency
Vitamin B12 is stored in the liver, kidney and other body tissues, so a
deficiency is rare and is a result of many years of low B12 intake. Symptoms of
a B12 deficiency include numbness, pins-and-needles sensations, or a burning
feeling in the feet and hands. Fatigue, muscle weakness, confusion, loss of
memory and depression are other symptoms. The tongue may be red and inflamed and
diarrhea may occur. Heart disease, including high serum cholesterol may be
present. Anemia results from low vitamin B12 levels (megaloblastic) or from a
lack of intrinsic factor (pernicious) which is needed for B12 absorption from
the gut. Deficiencies are most common in the elderly and alcoholics.
Symptoms of Toxicity
No toxicity occurs from vitamin B12.
Dosage and Administration
The Recommended Daily Allowance for vitamin B12 is 2.0 micrograms per day. Mixed
vitamin supplements usually include 25 to 300 micrograms. Supplements in the
range of 1,000 to 5,000 micrograms per day have been given. Recommended doses
for pernicious anemia are 2,000 micrograms daily for 1 month, then 1,000
micrograms daily. For anxiety, 100 to 500 micrograms have been supplemented
daily. It is best to give vitamin B12 in combination with at least 400
micrograms of folic acid. The injectable form of vitamin B12 is the most common
form used in the United States. The oral tablet is just as effective when given
in adequate amounts and malabsorption problems are not present.
Dosage Forms
Cyanocobalamin is most common oral form of vitamin B12 but must be converted to
the active form once absorbed. Methylcobalamin is the only active form and is
needed to convert homocysteine to methionine (methyl donor).
Hydroxycobalamin is the injectable form.